Chromosomes are structures within the nucleus that contain DNA. They become visible during cell division and are the carriers of genetic information. Chromosomes are composed of chromatin fibers that coil and fold, making the chromosomes visible under a light microscope during cell division. Chromosomes vary in size and number between species. They contain DNA that is packaged with histone proteins to form chromatin. The basic repeating unit of chromatin is the nucleosome, which contains 146 base pairs of DNA wrapped around an octamer of histone proteins.
This document discusses chromosomes and their structure. Some key points:
- Chromosomes are thread-like structures found in the nucleus that contain DNA. They can be seen during cell division.
- Chromosomes come in different shapes depending on the location of the centromere. They also have two arms labeled p and q.
- Humans have 46 chromosomes in their somatic cells. The number varies between species but is consistent within a species.
- Chromosomes contain DNA that is tightly packaged and organized through proteins like histones to fit inside the nucleus. Nucleosomes and chromatin compaction allow for the dense packing of DNA.
This document discusses key aspects of chromosomes including their definition, history, structure, composition, size, shape, and number. Some main points:
- Chromosomes are rod-shaped structures that contain DNA and protein. They were first observed in 1875 and are best seen during cell division.
- Eukaryotic chromosomes vary in size from 0.5-7μm and can be rod-shaped, J-shaped, or V-shaped depending on centromere position. Each species has a distinct somatic and genetic chromosome number.
- Chromosomes are made up of DNA, RNA, and proteins. DNA provides the genetic code. Histone proteins make up 80% of chromosomal protein while non-
This document discusses karyotyping, which involves pairing and ordering chromosomes to provide a genome-wide snapshot of an individual. Karyotypes can reveal chromosomal abnormalities like changes in number (e.g. Down syndrome) or structure (e.g. deletions, duplications). Clinical cytogeneticists analyze human karyotypes to detect genetic anomalies involving large amounts of DNA. Karyotyping is becoming a diagnostic tool for birth defects, genetic disorders, and cancers.
This document discusses the structures and functions of heterochromatin and euchromatin. Heterochromatin is tightly packed and transcriptionally inactive, found near centromeres and telomeres. Euchromatin is loosely packed and contains most actively transcribed genes. The basic unit of DNA packing is the nucleosome, which involves DNA wound around histone proteins. Heterochromatin and euchromatin differ in their genetic activity, location within chromosomes, and condensation levels during interphase.
Chromosomes are structures that contain DNA and protein found in cells. They contain genes and other sequences that control functions. Chromosomes come in two types - prokaryotic chromosomes are usually circular DNA molecules while eukaryotic chromosomes contain linear DNA molecules organized into multiple structures. Chromosomes are made up of DNA, histone proteins, and other non-histone proteins. The DNA is tightly coiled and packaged into nucleosomes, which further coil to form higher-order structures. Centromeres and telomeres play important roles in cell division and chromosome stability. Chromosome number and structure can vary between species and provide insights into evolution.
This document discusses sex determination and sex expression in animals. It defines key terms like sex chromosomes, autosomes, and allosomes. It describes four main mechanisms of sex determination: sex characters, chromosomal sex determination, monogenic sex determination, and environmental sex determination. For chromosomal sex determination, it provides details on the XX-XY, XX-XO, XO-XX, and ZW-ZZ systems. It also discusses genic balance theory and sex mosaicism in Drosophila.
CHROMOSOMES - Dr. P. Saranraj, Assistant Professor, Department of Microbiology, Sacred Heart College (Autonomous), Tirupattur, Vellore District, Tamil Nadu, India.
This document discusses chromosomes and their structure. Some key points:
- Chromosomes are thread-like structures found in the nucleus that contain DNA. They can be seen during cell division.
- Chromosomes come in different shapes depending on the location of the centromere. They also have two arms labeled p and q.
- Humans have 46 chromosomes in their somatic cells. The number varies between species but is consistent within a species.
- Chromosomes contain DNA that is tightly packaged and organized through proteins like histones to fit inside the nucleus. Nucleosomes and chromatin compaction allow for the dense packing of DNA.
This document discusses key aspects of chromosomes including their definition, history, structure, composition, size, shape, and number. Some main points:
- Chromosomes are rod-shaped structures that contain DNA and protein. They were first observed in 1875 and are best seen during cell division.
- Eukaryotic chromosomes vary in size from 0.5-7μm and can be rod-shaped, J-shaped, or V-shaped depending on centromere position. Each species has a distinct somatic and genetic chromosome number.
- Chromosomes are made up of DNA, RNA, and proteins. DNA provides the genetic code. Histone proteins make up 80% of chromosomal protein while non-
This document discusses karyotyping, which involves pairing and ordering chromosomes to provide a genome-wide snapshot of an individual. Karyotypes can reveal chromosomal abnormalities like changes in number (e.g. Down syndrome) or structure (e.g. deletions, duplications). Clinical cytogeneticists analyze human karyotypes to detect genetic anomalies involving large amounts of DNA. Karyotyping is becoming a diagnostic tool for birth defects, genetic disorders, and cancers.
This document discusses the structures and functions of heterochromatin and euchromatin. Heterochromatin is tightly packed and transcriptionally inactive, found near centromeres and telomeres. Euchromatin is loosely packed and contains most actively transcribed genes. The basic unit of DNA packing is the nucleosome, which involves DNA wound around histone proteins. Heterochromatin and euchromatin differ in their genetic activity, location within chromosomes, and condensation levels during interphase.
Chromosomes are structures that contain DNA and protein found in cells. They contain genes and other sequences that control functions. Chromosomes come in two types - prokaryotic chromosomes are usually circular DNA molecules while eukaryotic chromosomes contain linear DNA molecules organized into multiple structures. Chromosomes are made up of DNA, histone proteins, and other non-histone proteins. The DNA is tightly coiled and packaged into nucleosomes, which further coil to form higher-order structures. Centromeres and telomeres play important roles in cell division and chromosome stability. Chromosome number and structure can vary between species and provide insights into evolution.
This document discusses sex determination and sex expression in animals. It defines key terms like sex chromosomes, autosomes, and allosomes. It describes four main mechanisms of sex determination: sex characters, chromosomal sex determination, monogenic sex determination, and environmental sex determination. For chromosomal sex determination, it provides details on the XX-XY, XX-XO, XO-XX, and ZW-ZZ systems. It also discusses genic balance theory and sex mosaicism in Drosophila.
CHROMOSOMES - Dr. P. Saranraj, Assistant Professor, Department of Microbiology, Sacred Heart College (Autonomous), Tirupattur, Vellore District, Tamil Nadu, India.
This document discusses chromosomal aberrations, including definitions, types, and examples. It covers:
- Karyotyping and identifying chromosomes by size, centromere location, and banding patterns.
- Types of chromosomal abnormalities like aneuploidy, polyploidy, deletions, duplications, inversions, and translocations.
- Specific chromosomal disorders in humans caused by abnormalities, such as Down syndrome, Turner syndrome, and Klinefelter syndrome.
The effects of chromosomal aberrations can range from minor to severe, depending on the type and extent of the genetic material affected. Identification and classification of aberrations provides insight into associated disease states and
Chromatin is composed of DNA wrapped around histone proteins, which allows it to be tightly packed in the cell nucleus. There are two main types of chromatin: euchromatin, which is loosely coiled and allows for transcription; and heterochromatin, which is tightly packed and generally not transcribed. DNA combines with histone proteins to form nucleosomes, which involve 146bp of DNA wrapped around an octamer of core histone proteins. Nucleosomes further fold into a 30nm fiber, which then loops and coils to allow the long DNA molecules to fit inside the cell nucleus.
Chromosomal theory best explains human sex determination. Females are XX and produce X-bearing eggs, making them homogametic. Males are XY and produce both X- and Y-bearing sperm, making them heterogametic. The presence of a Y chromosome results in male development due to Y-linked genes, while its absence results in female development. Other factors like genetic balance and hormones can influence sex development but not determination.
Chromosomes are organized structures that package DNA and proteins in eukaryotic cells. Bacterial genetic material is concentrated in the nucleoid as a single circular DNA chromosome. Eukaryotic cells contain linear chromosomes housed within the nucleus. Chromosomes are made up of DNA, histone proteins, and non-histone proteins. They contain genes and regulatory elements and vary in structure between species.
This document discusses the structure and function of ribosomes. It begins by introducing ribosomes as large, complex molecules found in all living cells that serve as the primary site of protein synthesis. The document then describes the structure of ribosomes, which consist of two subunits that come together during protein synthesis. It explains the three main steps of protein synthesis carried out by ribosomes - initiation, elongation, and termination - and the role of mRNA and tRNA in translating genetic code into proteins.
Giant chromosomes like lampbrush chromosomes and polytene chromosomes contain multiple copies of DNA that allow for high levels of gene expression and RNA transcription. Lampbrush chromosomes are very long with DNA loops and are found in vertebrate oocyte cells during meiosis. Polytene chromosomes contain up to 1000 copies of DNA, forming bands and puffs visible under light microscopes. Both help synthesize large amounts of RNA and proteins to support cell growth and development.
Sex determination is the process by which an organism develops as male or female. It can be identified by morphological, anatomical and physiological characteristics. Historically it was determined based on primary and secondary sex characteristics, but scientific study began after the discovery of sex chromosomes in 1902. There are two main theories of sex determination - genetic theories involving sex chromosomes and physiological theories related to metabolic differences. In most species, including humans, the presence of two X chromosomes determines female development while one X and one Y chromosome determines male development.
Chromosome structure and packaging of dnaDIPTI NARWAL
Chromosomes are structures that contain DNA and help transmit genetic information from parents to offspring. They exist in the nucleus of cells and vary in number between species. DNA is packaged into chromosomes through histone proteins that allow very long DNA strands to fit inside cells. DNA wraps around histone proteins to form structures called nucleosomes, which contain 147 base pairs of DNA wrapped around an octamer of histone proteins. Nucleosomes further compact DNA by forming a beads-on-a-string structure that can coil and fold, allowing the long DNA molecules to fit within cells.
Sex determination is controlled by sex chromosomes. In humans and many other species, females have two X chromosomes (XX) while males have one X and one Y chromosome (XY). The presence of a Y chromosome determines maleness, while its absence results in femaleness. There are two main systems - heterogametic males which include humans and heterogametic females found in some insects and fish. The ratio between X chromosomes and autosomes also influences sex determination in some species through a genic balance mechanism.
Nucleosomes are the fundamental repeating subunits of eukaryotic chromatin that package DNA into a compact structure. They are composed of 146 base pairs of DNA wrapped around an octamer of histone proteins, resembling beads on a string. This represents the first order of DNA compaction. Higher orders of compaction involve the nucleosomes winding further to form solenoid fibers, scaffold loops, chromatids, and finally full chromosomes. Nucleosomes allow the long DNA molecules to fit within cell nuclei while also regulating genetic expression.
Epistasis refers to the phenomenon where the effect of one gene is dependent on the presence of other genes. There are different types of epistatic interactions: dominant epistasis occurs when a dominant allele of one gene masks the effect of alleles at another gene locus; recessive epistasis occurs when a recessive allele of one gene hides the effects of alleles at another locus; and duplicate recessive genes, or complementary genes, produce the same phenotype only when both genes have homozygous recessive alleles. Epistasis can modify expected Mendelian ratios from crosses.
Chromosomes are made of chromatin fibers containing DNA and proteins. Each chromosome contains two chromatids joined at the centromere. The centromere divides the chromosome into short and long arms. During cell division, the centromere and attached kinetochore allow chromosomes to align and separate. Telomeres are repetitive DNA sequences at chromosome ends that prevent fusion and shorten with each cell division due to the end replication problem, in which DNA polymerase cannot fully replicate chromosome ends.
Chromosomes are thread-like structures found in the nucleus of cells that contain organized DNA. They come in two types - autosomes which control non-sex characteristics, and sex chromosomes which determine sex. Chromosomes exist in pairs and are made up of DNA, proteins, and RNA. They contain a centromere that joins sister chromatids and a telomere at each end to protect the chromosome. Chromosomes package and protect DNA, carry genetic information to make proteins, and are essential for cell division and reproduction.
Lampbrush chromosomes are large paired chromosomes found in the oocytes of many animal species during meiosis. They are characterized by thick loops of DNA that extend out from the chromosomal axis where intense transcription is occurring. This unusual structure allows for stockpiling of RNA and proteins that will be needed for early embryonic development prior to fertilization.
This document discusses chromosome structure and organization. It begins by listing components of chromosomes like centromeres, telomeres, and origins of replication. It then describes how genes are organized between centromeres and telomeres in eukaryotes. Genes can be relatively short with few introns in lower eukaryotes, and longer with many introns in higher eukaryotes. The document also discusses the differences between chromosomes and chromatin, homologous chromosome pairs, autosomes and sex chromosomes, and types of heterochromatin and euchromatin.
Sex chromosomes determine an organism's sex. In most animals, females have two of the same sex chromosome (XX) while males have two different ones (XY). Some organisms use other systems like ZW chromosomes. The discovery of sex chromosomes began in the late 1800s with observations of fireflies and grasshoppers. Sex is also determined by factors like temperature, parasites, size, metabolism and hormones in some species. In humans, the Y chromosome carries the SRY gene which triggers testis development.
This document discusses lethal alleles, which are alleles that cause death in an organism. It defines lethal alleles and provides a brief history of their discovery through early studies of coat color inheritance in mice. The document outlines four types of lethal alleles: early onset alleles that cause death early in life, late onset alleles that cause death late in life, conditional alleles that only cause death under certain environmental conditions, and semi-lethal alleles that only kill some individuals, not all. It provides the example of the Y gene in mice, which causes a yellow coat color but is lethal when present in the homozygous dominant state (YY), though not in the heterozygous or recessive states.
This document discusses multiple allelism, which refers to more than two alternative allelic forms of a gene occupying the same locus. It provides examples of multiple allelism in eye color in Drosophila, with 14 alleles producing different shades from white to red, and in human blood groups with the A, B, and O alleles. The characteristics of multiple alleles are described, including that only two alleles are present per individual. Multiple allelism in inheritance of blood groups and determining blood group combinations in offspring are also covered.
The document discusses the cell nucleus, providing details on its history, characteristics, structure, and functions. It describes how the nucleus was discovered in 1831 and named by Robert Brown. The nucleus is a membrane-bound organelle found at the center of eukaryotic cells that can vary in shape and size depending on the cell. It houses genetic material in the form of chromatin and chromosomes and directs protein synthesis, cell growth and regulation, and transportation between the nucleus and cytoplasm. The nucleus contains a nuclear membrane, nucleolus, chromatin, and DNA and serves as the command center of the cell.
This document provides an introduction to molecular biology. It defines molecular biology as the branch of biology that deals with macromolecules like proteins and nucleic acids that are essential for life. It describes the three domains of life - eukaryotes, prokaryotes, and archaea. Key differences between prokaryotic and eukaryotic cells are outlined. Basic components of molecular biology like nucleic acids, chromosomes, genes and genomes are defined. The central dogma of molecular biology is mentioned and examples of applications of molecular biology are provided.
Chromosomes are structures within the nucleus that carry genetic information. They are composed of DNA and proteins and are only visible during cell division. Chromosomes contain genes and come in varying numbers depending on the organism. They are organized into nucleosomes which aid in compactly packaging the long DNA molecules. Centromeres and telomeres are essential features that help segregate and provide stability to chromosomes during cell division.
Chromosomes are rod-shaped structures found in the nucleus that carry genetic information. They are most visible during cell division when they condense and thicken. Chromosomes vary in size between species but are generally between 1-30 micrometers long. They are made up of DNA and proteins. The number and structure of chromosomes is consistent within species but varies between species and can provide clues about evolutionary relationships. Key features of chromosomes include the centromere, which divides it into two arms, and the type (metacentric, acrocentric, etc.) which is determined by centromere position. Karyotypes map the complete set of chromosomes in an organism and can be used to identify species.
This document discusses chromosomal aberrations, including definitions, types, and examples. It covers:
- Karyotyping and identifying chromosomes by size, centromere location, and banding patterns.
- Types of chromosomal abnormalities like aneuploidy, polyploidy, deletions, duplications, inversions, and translocations.
- Specific chromosomal disorders in humans caused by abnormalities, such as Down syndrome, Turner syndrome, and Klinefelter syndrome.
The effects of chromosomal aberrations can range from minor to severe, depending on the type and extent of the genetic material affected. Identification and classification of aberrations provides insight into associated disease states and
Chromatin is composed of DNA wrapped around histone proteins, which allows it to be tightly packed in the cell nucleus. There are two main types of chromatin: euchromatin, which is loosely coiled and allows for transcription; and heterochromatin, which is tightly packed and generally not transcribed. DNA combines with histone proteins to form nucleosomes, which involve 146bp of DNA wrapped around an octamer of core histone proteins. Nucleosomes further fold into a 30nm fiber, which then loops and coils to allow the long DNA molecules to fit inside the cell nucleus.
Chromosomal theory best explains human sex determination. Females are XX and produce X-bearing eggs, making them homogametic. Males are XY and produce both X- and Y-bearing sperm, making them heterogametic. The presence of a Y chromosome results in male development due to Y-linked genes, while its absence results in female development. Other factors like genetic balance and hormones can influence sex development but not determination.
Chromosomes are organized structures that package DNA and proteins in eukaryotic cells. Bacterial genetic material is concentrated in the nucleoid as a single circular DNA chromosome. Eukaryotic cells contain linear chromosomes housed within the nucleus. Chromosomes are made up of DNA, histone proteins, and non-histone proteins. They contain genes and regulatory elements and vary in structure between species.
This document discusses the structure and function of ribosomes. It begins by introducing ribosomes as large, complex molecules found in all living cells that serve as the primary site of protein synthesis. The document then describes the structure of ribosomes, which consist of two subunits that come together during protein synthesis. It explains the three main steps of protein synthesis carried out by ribosomes - initiation, elongation, and termination - and the role of mRNA and tRNA in translating genetic code into proteins.
Giant chromosomes like lampbrush chromosomes and polytene chromosomes contain multiple copies of DNA that allow for high levels of gene expression and RNA transcription. Lampbrush chromosomes are very long with DNA loops and are found in vertebrate oocyte cells during meiosis. Polytene chromosomes contain up to 1000 copies of DNA, forming bands and puffs visible under light microscopes. Both help synthesize large amounts of RNA and proteins to support cell growth and development.
Sex determination is the process by which an organism develops as male or female. It can be identified by morphological, anatomical and physiological characteristics. Historically it was determined based on primary and secondary sex characteristics, but scientific study began after the discovery of sex chromosomes in 1902. There are two main theories of sex determination - genetic theories involving sex chromosomes and physiological theories related to metabolic differences. In most species, including humans, the presence of two X chromosomes determines female development while one X and one Y chromosome determines male development.
Chromosome structure and packaging of dnaDIPTI NARWAL
Chromosomes are structures that contain DNA and help transmit genetic information from parents to offspring. They exist in the nucleus of cells and vary in number between species. DNA is packaged into chromosomes through histone proteins that allow very long DNA strands to fit inside cells. DNA wraps around histone proteins to form structures called nucleosomes, which contain 147 base pairs of DNA wrapped around an octamer of histone proteins. Nucleosomes further compact DNA by forming a beads-on-a-string structure that can coil and fold, allowing the long DNA molecules to fit within cells.
Sex determination is controlled by sex chromosomes. In humans and many other species, females have two X chromosomes (XX) while males have one X and one Y chromosome (XY). The presence of a Y chromosome determines maleness, while its absence results in femaleness. There are two main systems - heterogametic males which include humans and heterogametic females found in some insects and fish. The ratio between X chromosomes and autosomes also influences sex determination in some species through a genic balance mechanism.
Nucleosomes are the fundamental repeating subunits of eukaryotic chromatin that package DNA into a compact structure. They are composed of 146 base pairs of DNA wrapped around an octamer of histone proteins, resembling beads on a string. This represents the first order of DNA compaction. Higher orders of compaction involve the nucleosomes winding further to form solenoid fibers, scaffold loops, chromatids, and finally full chromosomes. Nucleosomes allow the long DNA molecules to fit within cell nuclei while also regulating genetic expression.
Epistasis refers to the phenomenon where the effect of one gene is dependent on the presence of other genes. There are different types of epistatic interactions: dominant epistasis occurs when a dominant allele of one gene masks the effect of alleles at another gene locus; recessive epistasis occurs when a recessive allele of one gene hides the effects of alleles at another locus; and duplicate recessive genes, or complementary genes, produce the same phenotype only when both genes have homozygous recessive alleles. Epistasis can modify expected Mendelian ratios from crosses.
Chromosomes are made of chromatin fibers containing DNA and proteins. Each chromosome contains two chromatids joined at the centromere. The centromere divides the chromosome into short and long arms. During cell division, the centromere and attached kinetochore allow chromosomes to align and separate. Telomeres are repetitive DNA sequences at chromosome ends that prevent fusion and shorten with each cell division due to the end replication problem, in which DNA polymerase cannot fully replicate chromosome ends.
Chromosomes are thread-like structures found in the nucleus of cells that contain organized DNA. They come in two types - autosomes which control non-sex characteristics, and sex chromosomes which determine sex. Chromosomes exist in pairs and are made up of DNA, proteins, and RNA. They contain a centromere that joins sister chromatids and a telomere at each end to protect the chromosome. Chromosomes package and protect DNA, carry genetic information to make proteins, and are essential for cell division and reproduction.
Lampbrush chromosomes are large paired chromosomes found in the oocytes of many animal species during meiosis. They are characterized by thick loops of DNA that extend out from the chromosomal axis where intense transcription is occurring. This unusual structure allows for stockpiling of RNA and proteins that will be needed for early embryonic development prior to fertilization.
This document discusses chromosome structure and organization. It begins by listing components of chromosomes like centromeres, telomeres, and origins of replication. It then describes how genes are organized between centromeres and telomeres in eukaryotes. Genes can be relatively short with few introns in lower eukaryotes, and longer with many introns in higher eukaryotes. The document also discusses the differences between chromosomes and chromatin, homologous chromosome pairs, autosomes and sex chromosomes, and types of heterochromatin and euchromatin.
Sex chromosomes determine an organism's sex. In most animals, females have two of the same sex chromosome (XX) while males have two different ones (XY). Some organisms use other systems like ZW chromosomes. The discovery of sex chromosomes began in the late 1800s with observations of fireflies and grasshoppers. Sex is also determined by factors like temperature, parasites, size, metabolism and hormones in some species. In humans, the Y chromosome carries the SRY gene which triggers testis development.
This document discusses lethal alleles, which are alleles that cause death in an organism. It defines lethal alleles and provides a brief history of their discovery through early studies of coat color inheritance in mice. The document outlines four types of lethal alleles: early onset alleles that cause death early in life, late onset alleles that cause death late in life, conditional alleles that only cause death under certain environmental conditions, and semi-lethal alleles that only kill some individuals, not all. It provides the example of the Y gene in mice, which causes a yellow coat color but is lethal when present in the homozygous dominant state (YY), though not in the heterozygous or recessive states.
This document discusses multiple allelism, which refers to more than two alternative allelic forms of a gene occupying the same locus. It provides examples of multiple allelism in eye color in Drosophila, with 14 alleles producing different shades from white to red, and in human blood groups with the A, B, and O alleles. The characteristics of multiple alleles are described, including that only two alleles are present per individual. Multiple allelism in inheritance of blood groups and determining blood group combinations in offspring are also covered.
The document discusses the cell nucleus, providing details on its history, characteristics, structure, and functions. It describes how the nucleus was discovered in 1831 and named by Robert Brown. The nucleus is a membrane-bound organelle found at the center of eukaryotic cells that can vary in shape and size depending on the cell. It houses genetic material in the form of chromatin and chromosomes and directs protein synthesis, cell growth and regulation, and transportation between the nucleus and cytoplasm. The nucleus contains a nuclear membrane, nucleolus, chromatin, and DNA and serves as the command center of the cell.
This document provides an introduction to molecular biology. It defines molecular biology as the branch of biology that deals with macromolecules like proteins and nucleic acids that are essential for life. It describes the three domains of life - eukaryotes, prokaryotes, and archaea. Key differences between prokaryotic and eukaryotic cells are outlined. Basic components of molecular biology like nucleic acids, chromosomes, genes and genomes are defined. The central dogma of molecular biology is mentioned and examples of applications of molecular biology are provided.
Chromosomes are structures within the nucleus that carry genetic information. They are composed of DNA and proteins and are only visible during cell division. Chromosomes contain genes and come in varying numbers depending on the organism. They are organized into nucleosomes which aid in compactly packaging the long DNA molecules. Centromeres and telomeres are essential features that help segregate and provide stability to chromosomes during cell division.
Chromosomes are rod-shaped structures found in the nucleus that carry genetic information. They are most visible during cell division when they condense and thicken. Chromosomes vary in size between species but are generally between 1-30 micrometers long. They are made up of DNA and proteins. The number and structure of chromosomes is consistent within species but varies between species and can provide clues about evolutionary relationships. Key features of chromosomes include the centromere, which divides it into two arms, and the type (metacentric, acrocentric, etc.) which is determined by centromere position. Karyotypes map the complete set of chromosomes in an organism and can be used to identify species.
Chromosomes are structures within cells that carry genetic information in the form of DNA. They are only visible during cell division. Chromosomes are composed of chromatin fibers that coil and fold, making the chromosomes visible under a light microscope during cell division. The number and size of chromosomes vary between species but provide the basic genetic information. Key parts of chromosomes include the centromere, which divides the chromosome into arms and attaches to spindle fibers during cell division, and the telomeres at the ends, which provide stability.
Chromosomes are structures that carry genetic information in the form of DNA. They are located within the nucleus of cells.
Chromosomes contain genes arranged in specific locations along chromatin. Different species have varying numbers of chromosomes depending on their genome size. Chromosomes contain features like centromeres, chromatids, and telomeres that allow for their movement and protection during cell division. Chromosomes are classified based on centromere position and carry out essential functions like cell division, inheritance of traits, and sex determination.
Chromosomes are structures in the nucleus that contain genetic material. They are complexes of DNA and proteins. Chromosomes are visible during cell division and come in different sizes. The number and structure of chromosomes provide identifying characteristics for different organisms and species. Chromosomes contain both euchromatin and heterochromatin regions that are identifiable by their staining patterns.
presentation on chromosome morphology and karyotypeasifaslam76778
The document discusses the structure and composition of chromosomes. It defines key terms like chromatid, centromere, and telomere. It describes the four classes of chromosomes based on centromere position - metacentric, submetacentric, acrocentric, and telocentric. The document also discusses heterochromatin, euchromatin, karyotypes, and the chemical composition of chromosomes, including DNA, histones, and non-histone proteins.
Chromosomes are thread-like structures located inside the nucleus of animal and plant cells. Each chromosome is made of protein and a single molecule of deoxyribonucleic acid (DNA). Passed from parents to offspring, DNA contains the specific instructions that make each type of living creature unique.
The nucleus is the control center of eukaryotic cells that contains DNA. It has a nuclear envelope with pores that regulates transport. The nucleoplasm is a liquid inside the envelope. The nucleolus produces ribosomes. Chromatin contains DNA and proteins. Chromosomes within the nucleus contain DNA and replicate during cell division. The centromere divides each chromosome into two chromatids and determines chromosome shape. The nucleus separates DNA from the cell's metabolic processes and transports materials via the nuclear envelope.
Types of chromosomes, basic structural features, chromosomal numbers, chromosomal banding, molecular organization of eukaryotic chromosome, MARS/SARS. Heterochromatin, euchromatin structures; structural organization of centromeric region, components and structure of Kinetochore, difference between mitotic kinetochores and meiotic kinetochores; structural organization of telomeres, proteins involved in heterochromatization of telomeric regions. Structural organization and molecular biology of salivary gland and Lampbrush chromosomes, importance of their study at specific stages of development.
This document provides an overview of chromosomes. It begins by defining a chromosome as a structure that carries genetic information in the form of genes. Chromosomes are located in the cell nucleus and are made up of DNA and protein. The total complement of genes in an organism makes up its genome, which can be stored on one or more chromosomes. In humans, there are usually 22 pairs of autosomes and one pair of sex chromosomes, for a total of 46 chromosomes. The document then discusses chromosome structure, the different types of chromosomes, the functions of chromosomes, and differences between prokaryotic and eukaryotic chromosomes. It concludes by defining chromosome aberrations and describing the two main types: structural and numerical aberrations.
Chromosomes are structures that carry genes within cells. They are made of DNA tightly coiled around histone proteins. The number and structure of chromosomes varies between species. Genes are segments of DNA that code for proteins and control inheritance of traits. They are located on chromosomes and there can be thousands of genes in a single cell. DNA replication and gene expression ensure genes are passed from parents to offspring.
Chromosomes are structures within cells that carry genetic information in the form of DNA. They exist in pairs and humans normally have 46 chromosomes total. Chromosomes are made up of DNA, proteins, and are visible during cell division. They compact DNA and carry genes that code for the production of proteins and inheritance of traits. Chromosomes undergo different levels of coiling and condensation within cells and can be classified based on features like centromere placement and size.
Chromosomes are structures in the nucleus that carry genetic information from one generation to the next. They play a vital role in cell division, heredity, and genetic inheritance. Chromosomes are made up of DNA and proteins, and vary in size, shape, and number between different species. They have various structures like chromatids, centromeres, and telomeres that allow them to duplicate and segregate accurately during cell division. Specific types of chromosomes include polytene chromosomes found in insect cells and lampbrush chromosomes found in animal oocytes. Chromosomes function to protect DNA and regulate gene expression essential for growth, reproduction, and repair of organisms.
This document discusses the morphology and types of chromosomes. It begins by defining what a chromosome is and where they are located in prokaryotic and eukaryotic cells. It then describes the different structural features of chromosomes visible under a light microscope, including chromatids, centromeres, secondary constrictions, telomeres, and satellites. It explains the different types of chromosomes based on centromere position, number of centromeres, size, and composition. The key differences between heterochromatin and euchromatin are also summarized.
Chromosomes are thread-like structures found in the nucleus that carry genetic information in the form of genes. They were first discovered in 1875 by Strasburger during cell division and were named chromosomes by Waldeyer in 1888. Chromosomes are visible under a microscope during metaphase when stained with suitable dyes. They occur in a definite number and shape in the cells of eukaryotic organisms and can be autosomes or sex chromosomes.
Chromosomes are thread-like structures in the nucleus that contain DNA. They condense during cell division and duplicate their DNA before splitting into two identical copies in each daughter cell. The number and structure of chromosomes provide important genetic information. Key points are that chromosomes contain DNA, duplicate before cell division, and determine species traits through their number and structure.
Definition of chromosomes and it's functionsirishalburo550
Chromosomes are structures that carry hereditary information in the form of genes. Each chromosome contains DNA and protein. There are different types of chromosomes, including autosomes that determine physical traits and sex chromosomes that determine sex. Chromosomes have a complex structure with regions like the centromere and telomeres that allow for cell division. They perform essential functions like DNA replication, gene expression, and transmitting traits from parents to offspring.
Chromosomes are DNA molecules that package genes and hereditary material. They exist in eukaryotic cells and contain DNA, proteins, and regulatory elements. Chromosomes have a complex structure, condensing through multiple levels to form compact metaphase chromosomes. They vary in size, shape, and number between species. Special types of chromosomes include polytene chromosomes found in insect larvae and lampbrush chromosomes seen during vertebrate meiosis. Karyotyping allows identification of chromosomes based on number, length, centromere position, and other features. Staining techniques are used to visualize chromosomes and study their structure.
This document discusses gene regulation in prokaryotes and eukaryotes. It explains that gene regulation allows cells to only express genes when they are needed. In prokaryotes, gene regulation typically occurs through operons at the transcriptional level. Eukaryotic gene regulation is more complex and can occur through epigenetic, transcriptional, post-transcriptional, translational and post-translational mechanisms. Key methods of regulation include chromatin remodeling, transcription factor binding, RNA processing, mRNA degradation, and protein degradation.
Ribosomes are sub-microscopic organelles found in all living cells that are the sites of protein synthesis. They are composed of ribosomal RNA and proteins. Ribosomes exist in two types - 70S ribosomes in prokaryotes and 80S ribosomes in eukaryotes. 70S ribosomes are composed of a 50S and 30S subunit while 80S ribosomes have a 60S and 40S subunit. Ribosomes contain three functional sites - the mRNA binding site, the aminoacyl-tRNA site (A site), and the peptidyl-tRNA site (P site) where protein synthesis occurs through the joining of amino acids. Ribosomes provide enzymes and factors to facilitate the
Vacuoles are membrane-bound organelles found in plant and fungal cells that function to store waste, nutrients, and water to regulate pressure within the cell. The cell wall is located outside the plasma membrane in plant, fungal, and some bacterial and algal cells and provides structure, protection, and allows for cell growth and communication. The nucleus houses the cell's genetic material and has a surrounding membrane with pores to allow transport of molecules in and out. Peroxisomes are spherical organelles found in all eukaryotic cells that contain enzymes for metabolic processes. The cytosol is the liquid within the cell and cytoplasm but outside organelles, and serves functions of transport, metabolism, and signaling.
Biotechnology has been used for millennia to improve agriculture, food production, and medicine through techniques like animal husbandry and fermentation. Modern biotechnology applies scientific principles to processing materials through biological agents. It has applications in medicine like drug development, agriculture like developing pest-resistant crops, and industry like producing chemicals. Biotechnology's scope continues expanding in fields such as genetic engineering, stem cell research, and environmental remediation.
unit 1 cytoskeletal structures ECM docx.pdf sh.pdfMSCW Mysore
The cytoskeleton is made up of three main components - microtubules, microfilaments, and intermediate filaments. Microtubules are hollow tubes made of tubulin dimers that help maintain cell shape and transport vesicles. Microfilaments are made of actin and enable cell movement and division. Intermediate filaments provide structural support and anchor organelles. The extracellular matrix of animal cells contains collagen, fibronectin and proteoglycans, while plant cells have a cell wall made of cellulose and pectin.
Biotechnology III sem Practical manual MSCW Mysore
This document contains laboratory protocols for experiments in cell biology and genetics. It includes procedures for observing mitosis in onion root tip cells using a squash technique, studying meiosis in onion flower bud cells using a permanent slide, examining Barr bodies in human buccal smear cells, and isolating chloroplasts from spinach leaves and mitochondria from yeast cells through differential centrifugation. The document provides detailed methodologies, materials required, and expected observations for each experiment to analyze key cellular processes like the cell cycle, meiosis, and intracellular organelle isolation.
This document discusses vitamins, classifying them as either fat-soluble or water-soluble. Fat-soluble vitamins include A, D, E, and K and are absorbed with fats. Water-soluble vitamins include vitamin C and the B complex vitamins. The B complex vitamins act as coenzymes in energy production and metabolism. The document provides details on functions, deficiency and toxicity symptoms, and food sources for several important vitamins.
Waste water treatment technology SH/pdfMSCW Mysore
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The document discusses different types of biomolecules, focusing on carbohydrates. It defines carbohydrates and describes their classification into monosaccharides, disaccharides, oligosaccharides, and polysaccharides. The key monosaccharides discussed are glucose, fructose, and galactose. Major disaccharides include sucrose, maltose, and lactose. Carbohydrates can exist in both chain and ring forms.
This document provides information about career options in biotechnology. It discusses the various academic and industry career paths available with undergraduate, postgraduate, and PhD degrees in biotechnology and related fields. Specific job roles are outlined for research assistants, research associates, senior research associates, scientists, principal scientists, scientific directors, and bioinformatics scientists. The document also provides details on the Indian biotechnology industry and job market size, key organizations, and tips for pursuing opportunities in biotechnology.
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practical manual on molecular biology and genetic engineering,recombinant DNA...MSCW Mysore
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A workshop hosted by the South African Journal of Science aimed at postgraduate students and early career researchers with little or no experience in writing and publishing journal articles.
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There are 4 phases of wound healing: hemostasis, inflammation, proliferation, and remodeling. This document also describes the mechanism of wound healing. Factors that affect healing include infection, uncontrolled diabetes, poor nutrition, age, anemia, the presence of foreign bodies, etc.
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Librarians are leading the way in creating future-ready citizens – now we need to update our spaces to match. In this session, attendees will get inspiration for transforming their library spaces. You’ll learn how to survey students and patrons, create a focus group, and use design thinking to brainstorm ideas for your space. We’ll discuss budget friendly ways to change your space as well as how to find funding. No matter where you’re at, you’ll find ideas for reimagining your space in this session.
Chapter wise All Notes of First year Basic Civil Engineering.pptxDenish Jangid
Chapter wise All Notes of First year Basic Civil Engineering
Syllabus
Chapter-1
Introduction to objective, scope and outcome the subject
Chapter 2
Introduction: Scope and Specialization of Civil Engineering, Role of civil Engineer in Society, Impact of infrastructural development on economy of country.
Chapter 3
Surveying: Object Principles & Types of Surveying; Site Plans, Plans & Maps; Scales & Unit of different Measurements.
Linear Measurements: Instruments used. Linear Measurement by Tape, Ranging out Survey Lines and overcoming Obstructions; Measurements on sloping ground; Tape corrections, conventional symbols. Angular Measurements: Instruments used; Introduction to Compass Surveying, Bearings and Longitude & Latitude of a Line, Introduction to total station.
Levelling: Instrument used Object of levelling, Methods of levelling in brief, and Contour maps.
Chapter 4
Buildings: Selection of site for Buildings, Layout of Building Plan, Types of buildings, Plinth area, carpet area, floor space index, Introduction to building byelaws, concept of sun light & ventilation. Components of Buildings & their functions, Basic concept of R.C.C., Introduction to types of foundation
Chapter 5
Transportation: Introduction to Transportation Engineering; Traffic and Road Safety: Types and Characteristics of Various Modes of Transportation; Various Road Traffic Signs, Causes of Accidents and Road Safety Measures.
Chapter 6
Environmental Engineering: Environmental Pollution, Environmental Acts and Regulations, Functional Concepts of Ecology, Basics of Species, Biodiversity, Ecosystem, Hydrological Cycle; Chemical Cycles: Carbon, Nitrogen & Phosphorus; Energy Flow in Ecosystems.
Water Pollution: Water Quality standards, Introduction to Treatment & Disposal of Waste Water. Reuse and Saving of Water, Rain Water Harvesting. Solid Waste Management: Classification of Solid Waste, Collection, Transportation and Disposal of Solid. Recycling of Solid Waste: Energy Recovery, Sanitary Landfill, On-Site Sanitation. Air & Noise Pollution: Primary and Secondary air pollutants, Harmful effects of Air Pollution, Control of Air Pollution. . Noise Pollution Harmful Effects of noise pollution, control of noise pollution, Global warming & Climate Change, Ozone depletion, Greenhouse effect
Text Books:
1. Palancharmy, Basic Civil Engineering, McGraw Hill publishers.
2. Satheesh Gopi, Basic Civil Engineering, Pearson Publishers.
3. Ketki Rangwala Dalal, Essentials of Civil Engineering, Charotar Publishing House.
4. BCP, Surveying volume 1
it describes the bony anatomy including the femoral head , acetabulum, labrum . also discusses the capsule , ligaments . muscle that act on the hip joint and the range of motion are outlined. factors affecting hip joint stability and weight transmission through the joint are summarized.
This slide is special for master students (MIBS & MIFB) in UUM. Also useful for readers who are interested in the topic of contemporary Islamic banking.
2. What Exactly is a
chromosome?
Chromosomes are the rod-shaped,
filamentous bodies present in the
nucleus, which become visible during
cell division.
They are the carriers of the gene or
unit of heredity.
Chromosome are not visible in active
nucleus due to their high water
content, but are clearly seen during
cell division.
3. Chromosomes were first described by Strausberger in 1875.
The term “Chromosome”, however was first used by Waldeyer in
1888.
They were given the name chromosome (Chromo = colour; Soma =
body) due to their marked affinity for basic dyes.
Their number can be counted easily only during mitotic
metaphase.
4. Chromosomes are composed of thin chromatin threads called
Chromatin fibers.
These fibers undergo folding, coiling and supercoiling during
prophase so that the chromosomes become progressively thicker
and smaller.
Therefore, chromosomes become readily observable under light
microscope.
At the end of cell division, on the other hand, the fibers uncoil
and extend as fine chromatin threads, which are not visible at
light microscope
5. Number of chromosomes
Normally, all the individuals of a species have
the same number of chromosomes.
Closely related species usually have similar
chromosome numbers.
Presence of a whole sets of chromosomes is
called euploidy.
It includes haploids, diploids, triploids,
tetraploids etc.
Gametes normally contain only one set of
chromosome – this number is called Haploid
Somatic cells usually contain two sets of
chromosome - 2n : Diploid
6. 3n – triploid
4n – tetraploid
The condition in which the chromosomes sets
are present in a multiples of “n” is Polyploidy
When a change in the chromosome number does
not involve entire sets of chromosomes, but
only a few of the chromosomes - is
Aneuploidy.
Monosomics (2n-1)
Trisomics (2n+1)
Nullisomics (2n-2)
Tetrasomics (2n+2)
9. On the extreme, round worm shows only two
chromosomes, while the other extreme is
represented by Protozoa having 300 or more
chromosomes.
However, most organisms have numbers between
12 to 50.
3-8 in fungi
From 8 – 16 in Angiosperms (Most common
number being 12).
10. Chromosome Size
In contrast to other cell organelles, the size of
chromosomes shows a remarkable variation
depending upon the stages of cell division.
Interphase: chromosome are longest & thinnest
Prophase: there is a progressive decrease in their
length accompanied with an increase in thickness
Anaphase: chromosomes are smallest.
Metaphase: Chromosomes are the most easily
observed and studied during metaphase when
they are very thick, quite short and well spread in
the cell.
Therefore, chromosomes measurements are
generally taken during mitotic metaphase.
11. The size of the chromosomes in mitotic phase of
animal and plants sp generally varies between
0.5 µ and 32 µ in length, and between 0.2 µ and
3.0 µ in diameter.
The longest metaphase chromosomes found in
Trillium - 32 µ.
The giant chromosomes found in diptera and they
may be as long as 300 µ and up to 10 µ in
diameter.
In general, plants have longer chromosomes than
animal and species having lower chromosome
numbers have long chromosomes than those
having higher chromosome numbers
Among plants, dicots in general, have a higher
number of chromosome than monocots.
Chromosomes are longer in monocot than dicots.
12. In order to understand chromosomes and their
function, we need to be able to discriminate
among different chromosomes.
First, chromosomes differ greatly in size
Between organisms the size difference can be
over 100-fold, while within a sp, some
chromosomes are often 10 times as large as
others.
In a species Karyotype, a pictorial or
photographic representation of all the different
chromosomes in a cell of an individual,
chromosomes are usually ordered by size and
numbered from largest to smallest.
14. Karyotype: is the general morphology of the
somatic chromosome. Generally, karyotypes
represent by arranging in the descending order of
size keeping their centromeres in a straight line.
Idiotype: the karyotype of a species may be
represented diagrammatically, showing all the
morphological features of the chromosome; such
a diagram is known as Idiotype.
15. Chromosomes may differ in the position of the Centromere,
the place on the chromosome where spindle fibers are
attached during cell division.
In general, if the centromere is near the middle, the
chromosome is metacentric
If the centromere is toward one end, the chromosome is
acrocentric or submetacentric
If the centromere is very near the end, the chromosome is
telocentric.
16.
17. The centromere divides the chromosome
into two arms, so that, for example, an
acrocentric chromosome has one short and
one long arm,
While, a metacentric chromosome has arms
of equal length.
All house mouse chromosomes are
telocentric, while human chromosomes
include both metacentric and acrocentric,
but no telocentric.
18. Euchromatin and
Heterochromatin
Chromosomes may be identified by regions that
stain in a particular manner when treated with
various chemicals.
Several different chemical techniques are used to
identify certain chromosomal regions by staining
then so that they form chromosomal bands.
For example, darker bands are generally found
near the centromeres or on the ends (telomeres)
of the chromosome, while other regions do not
stain as strongly.
The position of the dark-staining are
heterochromatic region or heterochromatin.
Light staining are euchromatic region or
euchromatin.
19. Heterochromatin is classified into two
groups: (i) Constitutive and (ii) Facultative.
Constitutive heterochromatin remains
permanently in the heterochromatic stage,
i.e., it does not revert to the euchromatic
stage.
In contrast, facultative heterochromatin
consists of euchromatin that takes on the
staining and compactness characteristics of
heterochromatin during some phase of
development.
20. Satellite DNAs
When the DNA of a prokaryote, such as E.coli, is
isolated, fragmented and centrifuged to
equilibrium in a Cesium chloride (CsCl) density
gradient, the DNA usually forms a single band in
the gradient.
On the other hand, CsCl density-gradient analysis
of DNA from eukaryotes usually reveals the
presence of one large band of DNA (usually
called “Mainband” DNA) and one to several
small bands.
These small bands are referred to as “Satellite
DNAs”.
For e.g., in Drosophila virilis, contain three distinct
satellite DNAs.
22. Not only the genomes of eukaryotes are more complex than
prokaryotes, but the DNA of eukaryotic cell is also organized
differently from that of prokaryotic cells.
The genomes of prokaryotes are contained in single
chromosomes, which are usually circular DNA molecules.
In contrast, the genomes of eukaryotes are composed of
multiple chromosomes, each containing a linear molecular of
DNA.
23. Although the numbers and sizes of
chromosomes vary considerably between
different species, their basic structure is the
same in all eukaryotes
Organism Genome Chromosome
Size (Mb)a
numbera
Arabidopsis
thaliana 70 5
Corn 5000 10
Onion 15,000 8
Lily 50,000 12
Fruit fly 165 4
Chicken 50,000 39
Mouse 1,200 20
Cow 3000 30
Human 3000 23
a – both genome size and chromosome numbers are for
haploid cells
24. The DNA of eukaryotic cell is tightly bound to
small basic proteins (histones) that package the
DNA in an orderly way in the cell nucleus.
This task is substantial (necessary), given the
DNA content of most eukaryotes
For e.g., the total extended length of DNA in a
human cell is nearly 2 m, but this must be fit into
a nucleus with a diameter of only 5 to 10µm.
Although DNA packaging is also a problem in
bacteria, the mechanism by which prokaryotic
DNA are packaged in the cell appears distinct
from that eukaryotes and is not well
understood.
25. Prokaryotic chromosome
The prokaryotes usually have
only one chromosome, and it
bears little morphological
resemblance to eukaryotic
chromosomes.
Among prokaryotes there is
considerable variation in
genome length bearing
genes.
The genome length is smallest
in RNA viruses
In this case, the organism is
provided with only a few
genes in its chromosome.
The number of gene may be
as high as 150 in some larger
bacteriophage genome.
26. In E.coli, about 3000 to 4000 genes are
organized into its one circular chromosome.
The chromosome exists as a highly folded
and coiled structure dispersed throughout
the cell.
The folded nature of chromosome is due to
the incorporation of RNA with DNA.
There are about 50 loops in the
chromosome of E.coli.
These loops are highly twisted or supercoiled
structure with about four million nucleotide
pairs.
Its molecular weight is about 2.8 X109
During replication of DNA, the coiling must
be relaxed.
DNA gyrase is necessary for the unwinding
the coils.
29. Supercoiling
The helix twists
on itself; twists
to the right Helix twists on
itself in the opposite
direction; twists to
the left
Most common type
of supercoiling
30. Mechanism of folding of a bacterial chromosomeMechanism of folding of a bacterial chromosome
There are many supercoiled loops (~100 in E. coli) attached to a
central core. Each loop can be independently relaxed or condensed.
Topoisomerase enzyme – (Type I and II) that introduce or remove
supercoiling.
31. Chromatin
The complexes between eukaryotic DNA and
proteins are called Chromatin, which typically
contains about twice as much protein as DNA.
The major proteins of chromatin are the histones
– small proteins containing a high proportion of
basic aminoacids (arginine and lysine) that
facilitate binding negatively charged DNA
molecule .
There are 5 major types of histones: H1, H2A,
H2B, H3, and H4 – which are very similar among
different sp of eukaryotes.
The histones are extremely abundant proteins in
eukaryotic cells.
Their mass is approximately equal to that of the
cell’s DNA
32. The major histone proteins:
Histone Mol. Wt No. of Percentage
Amino acidLys + Arg
H1 22,500244 30.8
H2A 13,960129 20.2
H2B 13,774125 22.4
H3 15,273135 22.9
H4 11,236102 24.5
The DNA double helix is bound to proteins called histones. The
histones have positively charged (basic) amino acids to bind the
negatively charged (acidic) DNA. Here is an SDS gel of histone
proteins, separated by size
33. In addition, chromatin contains an approximately
equal mass of a wide variety of non-histone
chromosomal proteins.
There are more than a thousand different types of
these proteins, which are involved in a range of
activities, including DNA replication and gene
expression.
The DNA of prokaryotes is similarly associated with
proteins, some of which presumably function as
histones do, packing the DNA within the bacterial
cell.
Histones, however are unique feature of
eukaryotic cells and are responsible for distinct
structural organization of eukaryotic chromatin
34. The basic structural unit of chromatin, the nucleosome,
was described by Roger Kornberg in 1974.
Two types of experiments led to Kornberg’s proposal of
the nucleosome model.
First, partial digestion of chromatin with micrococcal
nuclease (an enzyme that degrades DNA) was found to
yield DNA fragments approximately 200 base pairs long.
In contrast, a similar digestion of naked DNA (not
associated with protein) yielded a continuous smear
randomly sized fragments.
These results suggest that the binding of proteins to DNA
in chromatin protects the regions of DNA from
nuclease digestion, so that enzyme can
attack DNA only at sites separated by
approximately 200 base pairs.
35. Electron microscopy revealed that chromatin fibers have a
beaded appearance, with the beads spaced at intervals of
approximately 200 base pairs.
Thus, both nuclease digestion and the electron microscopic
studies suggest that chromatin is composed of repeating 200
base pair unit, which were called nucleosome.
37. Detailed analysis of these nucleosome core particles has
shown that they contain 146 base pairs of DNA wrapped 1.75
times around a histone core consisting of two molecules each
of H2A, H2B, H3, and H4 (the core histones).
One molecule of the fifth histone H1, is bound to the DNA as it
enters and exists each nucleosome core particle.
This forms a chromatin subunit known as chromatosome,
which consist of 166 base pairs of DNA wrapped around
histone core and held in place by H1 (a linker histone)
38.
39.
40.
41.
42.
43.
44. Centromeres and Telomeres
Centromeres and telomeres are two essential features of all
eukaryotic chromosomes.
Each provide a unique function i.e., absolutely necessary for
the stability of the chromosome.
Centromeres are required for the segregation of the
centromere during meiosis and mitosis.
Teleomeres provide terminal stability to the chromosome and
ensure its survival
45. Centromere
The region where two sister chromatids of a
chromosome appear to be joined or “held together”
during mitatic metaphase is called Centromere
When chromosomes are stained they typically show a
dark-stained region that is the centromere.
Also termed as Primary constriction
During mitosis, the centromere that is shared by the
sister chromatids must divide so that the chromatids can
migrate to opposite poles of the cell.
On the other hand, during the first meiotic division the
centromere of sister chromatids must remain intact
whereas during meiosis II they must act as they do
during mitosis.
Therefore the centromere is an important component of
chromosome structure and segregation.
46. As a result, centromeres are the first parts of
chromosomes to be seen moving towards the
opposite poles during anaphase.
The remaining regions of chromosomes lag
behind and appear as if they were being pulled
by the centromere.
47. Kinetochore
Within the centromere region, most species have several
locations where spindle fibers attach, and these sites consist
of DNA as well as protein.
The actual location where the attachment occurs is called
the kinetochore and is composed of both DNA and protein.
The DNA sequence within these regions is called CEN DNA.
48. Typically CEN DNA is about 120 base pairs long and consists of
several sub-domains, CDE-I, CDE-II and CDE-III.
Mutations in the first two sub-domains have no effect upon
segregation,
but a point mutation in the CDE-III sub-domain completely
eliminates the ability of the centromere to function during
chromosome segregation.
Therefore CDE-III must be actively involved in the binding of
the spindle fibers to the centromere.
49. The protein component of the kinetochore is only
now being characterized.
A complex of three proteins called Cbf-III binds to
normal CDE-III regions but can not bind to a CDE-
III region with a point mutation that prevents
mitotic segregation.
50. Telomere
The two ends of a chromosome are known as telomeres.
It required for the replication and stability of the chromosome.
When telomeres are damaged or removed due to chromosome
breakage, the damaged chromosome ends can readily fuse or
unite with broken ends of other chromosome.
Thus it is generally accepted that structural integrity and
individuality of chromosomes is maintained due to telomeres.
51. McClintock noticed that if two
chromosomes were broken in a cell,
the end of one could attach to the
other and vice versa.
What she never observed was the
attachment of the broken end to the
end of an unbroken chromosome.
Thus the ends of broken chromosomes
are sticky, whereas the normal end is
not sticky, suggesting the ends of
chromosomes have unique features.
52. Telomere Repeat Sequences
until recently, little was known about molecular
structure of telomeres. However, during the last few
years, telomeres have been isolated and
characterized from several sp.
Species Repeat Sequence
Arabidopsis TTTAGGG
Human TTAGGG
Oxytricha TTTTGGGG
Slime Mold TAGGG
Tetrahymena TTGGGG
Trypanosome TAGGG
53. The telomeres of this
organism end in the
sequence 5'-TTGGGG-3'.
The telomerase adds a
series of 5'-TTGGGG-3'
repeats to the ends of the
lagging strand.
A hairpin occurs when
unusual base pairs
between guanine residues
in the repeat form.
Finally, the hairpin is
removed at the 5'-
TTGGGG-3' repeat.
Thus the end of the
chromosome is faithfully
replicated.
TetrahymenaTetrahymena - protozoa- protozoa
organism.organism.
RNA Primer - Short stretches of
ribonucleotides (RNA substrates) found on the
lagging strand during DNA replication. Helps
initiate lagging strand replication
54. Staining and Banding chromosome
Staining procedures have been developed in the past
two decades and these techniques help to study
the karyotype in plants and animals.
1. Feulgen Staining:
Cells are subjected to a mild hydrolysis in 1N HCl
at 600
C for 10 minutes.
This treatment produces a free aldehyde group in
deoxyribose molecules.
When Schiff’s reagent (basic fuschin bleached
with sulfurous acid) to give a deep pink colour.
Ribose of RNA will not form an aldehyde under
these conditions, and the reaction is thus specific
for DNA
55. 2. Q banding:
The Q bands are the fluorescent bands
observed after quinacrine mustard staining
and observation with UV light.
The distal ends of each chromatid are not
stained by this technique.
The Y chromosome become brightly
fluorescent both in the interphase and in
metaphase.
3. R banding:
The R bands (from reverse) are those located
in the zones that do not fluoresce with the
quinacrine mustard, that is they are between
the Q bands and can be visualized as green.
56. 4. G banding:
The G bands (from Giemsa) have the same
location as Q bands and do not require
fluorescent microscopy.
Many techniques are available, each
involving some pretreatment of the
chromosomes.
In ASG (Acid-Saline-Giemsa) cells are
incubated in citric acid and NaCl for one
hour at 600
C and are then treated with the
Giemsa stain.
5. C banding:
The C bands correspond to constitutive
heterochromatin.
The heterochromatin regions in a
chromosome distinctly differ in their
stainability from euchromatic region.
58. Chromosomal Aberrations
The somatic (2n) and gametic (n) chromosome
numbers of a species ordinarily remain
constant.
This is due to the extremely precise mitotic and
meiotic cell division.
Somatic cells of a diploid species contain two
copies of each chromosome, which are called
homologous chromosome.
Their gametes, therefore contain only one copy
of each chromosome, that is they contain one
chromosome complement or genome.
Each chromosome of a genome contains a
definite numbers and kinds of genes, which are
arranged in a definite sequence.
59. Chromosomal Aberrations
Sometime due to mutation or spontaneous
(without any known causal factors), variation in
chromosomal number or structure do arise in
nature. - Chromosomal aberrations.
Chromosomal aberration may be grouped into
two broad classes:
1. Structural and 2. Numerical
60. Structural Chromosomal
Aberrations Chromosome structure variations result from chromosome
breakage.
Broken chromosomes tend to re-join; if there is more than one break,
rejoining occurs at random and not necessarily with the correct
ends.
The result is structural changes in the chromosomes.
Chromosome breakage is caused by X-rays, various chemicals, and
can also occur spontaneously.
61. There are four common type of structural aberrations:
1. Deletion or Deficiency
2. Duplication or Repeat
3. Inversion, and
4. Translocation.
62. Consider a normal chromosome with genes
in alphabetical order: a b c d e f g h i
1. Deletion: part of the chromosome has
been removed: a b c g h i
2. Dupliction: part of the chromosome is
duplicated:
a b c d e f d e f g h i
3. Inversion: part of the chromosome has
been re-inserted in reverse order: a b c f e
d g h i
ring: the ends of the chromosome are
joined together to make a ring
63. 4. translocation: parts of two non-homologous chromosomes are
joined:
If one normal chromosome is a b c d e f g h i and the other
chromosome is u v w x y z,
then a translocation between them would be
a b c d e f x y z and u v w g h i.
64.
65. Deletion or deficiency
Loss of a chromosome segment is known as
deletion or deficiency
It can be terminal deletion or interstitial or intercalary
deletion.
A single break near the end of the chromosome
would be expected to result in terminal deficiency.
If two breaks occur, a section may be deleted and
an intercalary deficiency created.
Terminal deficiencies might seem less complicated.
But majority of deficiencies detected are intercalary
type within the chromosome.
Deletion was the first structural aberration detected
by Bridges in 1917 from his genetic studies on X
chromosome of Drosophila.
66. Deletion generally produce striking genetic and
physiological effects.
When homozygous, most deletions are lethal,
because most genes are necessary for life and
a homozygous deletion would have zero copies
of some genes.
When heterozygous, the genes on the normal
homologue are hemizygous: there is only 1
copy of those genes.
Crossing over is absent in deleted region of a
chromosome since this region is present in only
one copy in deletion heterozygotes.
In Drosophila, several deficiencies induced the
mutants like Blond, Pale, Beaded, Carved,
Notch, Minute etc.
67. Deletion in Prokaryotes:
Deletions are found in prokaryotes as well, e.g.,
E.coli, T4 phage and Lambda phage.
In E.coli, deletions of up to 1 % of the bacterial
chromosome are known.
In lambda phage, however 20% of the genome
may be missing in some of the deletions.
Deletion in Human:
Chromosome deletions are usually lethal even
as heterozygotes, resulting in zygotic loss,
stillbirths, or infant death.
Sometimes, infants with small chromosome
deficiencies however, survive long enough to
permit the abnormal phenotype they express.
68. Cri-du-chat (Cat cry syndrome):
The name of the syndrome came from a catlike
mewing cry from small weak infants with the disorder.
Other characteristics are microcephaly (small head),
broad face and saddle nose, physical and mental
retardation.
Cri-du-chat patients die in infancy or early childhood.
The chromosome deficiency is in the short arm of
chromosome 5 .
Myelocytic leukemia
Another human disorder that is associated with a
chromosome abnormality is chronic myelocytic
leukemia.
A deletion of chromosome 22 was described by
P.C.Nowell and Hungerford and was called
“Philadelphia” (Ph’) chromosome after the city in
which the discovery was made.
69. Duplication
The presence of an additional chromosome segment, as
compared to that normally present in a nucleus is known as
Duplication.
In a diploid organism, presence of a chromosome segment in
more than two copies per nucleus is called duplication.
Four types of duplication:
1. Tandem duplication
2. Reverse tandem duplication
3. Displaced duplication
4. Translocation duplication
70. The extra chromosome segment may be located immediately
after the normal segment in precisely the same orientation forms
the tandem
When the gene sequence in the extra segment of a tandem in
the reverse order i.e, inverted , it is known as reverse tandem
duplication
In some cases, the extra segment may be located in the same
chromosome but away from the normal segment – termed as
displaced duplication
The additional chromosome segment is located in a non-
homologous chromosome is translocation duplication.
71. Origin
Origin of duplication involves chromosome
breakage and reunion of chromosome
segment with its homologous chromosome.
As a result, one of the two homologous
involved in the production of a duplication
ends up with a deficiency, while the other has
a duplication for the concerned segment.
Another phenomenon, known as unequal
crossing over, also leads to exactly the same
consequences for small chromosome
segments.
For e.g., duplication of the band 16A of X
chromosome of Drosophila produces Bar eye.
This duplication is believed to originate due to
unequal crossing over between the two
normal X chromosomes of female.
72.
73.
74. Inversion
When a segment of chromosome is oriented in the
reverse direction, such segment said to be inverted and
the phenomenon is termed as inversion.
The existence of inversion was first detected by Strutevant
and Plunkett in 1926.
Inversion occur when parts of chromosomes become
detached , turn through 1800
and are reinserted in such a
way that the genes are in reversed order.
For example, a certain segment may be broken in two
places, and the breaks may be in close proximity
because of chance loop in the chromosome.
When they rejoin, the wrong ends may become
connected.
The part on one side of the loop connects with broken
end different from the one with which it was formerly
connected.
This leaves the other two broken ends to become
attached.
The part within the loop thus becomes turned around or
75. Inversion may be classified into two types:
Pericentric - include the centromere
Paracentric - do not include the centromere
76. An inversion consists of two breaks in one chromosome.
The area between the breaks is inverted (turned around), and
then reinserted and the breaks then unite to the rest of the
chromosome.
If the inverted area includes the centromere it is called a
pericentric inversion.
If it does not, it is called a paracentric inversion.
77. Inversions in natural populations
In natural populations, pericentric inversions are much less
frequent than paracentric inversions.
In many sp, however, pericentric inversions are relatively
common, e.g., in some grasshoppers.
Paracentric inversions appear to be very frequent in natural
populations of Drosophila.
78. Translocation
Integration of a chromosome segment into a nonhomologous
chromosome is known as translocation.
Three types:
1. simple translocation
2. shift
3. reciprocal translocation.
79. Simple translocation: In this case, terminal segment of a
chromosome is integrated at one end of a non-homologous
region. Simple translocations are rather rare.
Shift: In shift, an intercalary segment of a chromosome is
integrated within a non-homologous chromosome. Such
translocations are known in the populations of Drosophila,
Neurospora etc.
Reciprocal translocation: It is produced when two non-
homologous chromosomes exchange segments – i.e.,
segments reciprocally transferred.
Translocation of this type is most common
80. Non-Disjunction
Generally during gametogenesis the homologous chromosomes
of each pair separate out (disjunction) and are equally
distributed in the daughter cells.
But sometime there is an unequal distribution of chromosomes in
the daughter cells.
The failure of separation of homologous chromosome is called
non-disjunction.
This can occur either during mitosis or meiosis or embryogenesis.
81.
82. Mitotic non-disjunction: The failure of separation
of homologous chromosomes during mitosis is
called mitotic non-disjunction.
It occurs after fertilization.
May happen during first or second cleavage.
Here, one blastomere will receive 45
chromosomes, while other will receive 47.
Meiotic non-disjunction: The failure of
separation of homologous chromosomes during
meiosis is called mitotic non-disjunction
Occurs during gametogensis
Here, one type contain 22 chromosome, while
other will be 24.
83. Variation in chromosome
number
Organism with one complete set of chromosomes is
said to be euploid (applies to haploid and diploid
organisms).
Aneuploidy - variation in the number of individual
chromosomes (but not the total number of sets of
chromosomes).
The discovery of aneuploidy dates back to 1916
when Bridges discovered XO male and XXY female
Drosophila, which had 7 and 9 chromosomes
respectively, instead of normal 8.
84. Nullisomy - loss of one homologous
chromosome pair. (e.g., Oat )
Monosomy – loss of a single
chromosome (Maize).
Trisomy - one extra chromosome.
(Datura)
Tetrasomy - one extra chromosome
pair.
More about Aneuploidy
85. Uses of Aneuploidy
They have been used to determine the phenotypic effect of loss
or gain of different chromosome
Used to produce chromosome substitution lines. Such lines yield
information on the effects of different chromosomes of a variety
in the same genetic background.
They are also used to produce alien addition and alien
substitution lines. These are useful in gene transfer from one
species to another.
Aneuploidy permits the location of a gene as well as of a
linkage group onto a specific chromosome.
86. Trisomy in Humans
Down Syndrome
The best known and most common chromosome
related syndrome.
Formerly known as “Mongolism”
1866, when a physician named John Langdon
Down published an essay in England in which he
described a set of children with common features
who were distinct from other children with mental
retardation he referred to as “Mongoloids.”
One child in every 800-1000 births has Down
syndrome
250,000 in US has Down syndrome.
The cost and maintaining Down syndrome case in
US is estimated at $ 1 billion per year.
87. Patients having Down syndrome will Short in stature (four feet tall)
and had an epicanthal fold, broad short skulls, wild nostrils, large
tongue, stubby hands
Some babies may have short necks, small hands, and short fingers.
They are characterized as low in mentality.
Down syndrome results if the extra chromosome is number 21.
88. Amniocentesis for Detecting Aneuploidy
Chromosomal abnormalities are sufficiently well understood to
permit genetic counseling.
A fetus may be checked in early stages of development by
karyotyping the cultured cells obtained by a process called
amniocentesis.
A sample of fluid will taken from mother and fetal cells are
cultured and after a period of two to three weeks,
chromosomes in dividing cells can be stained and observed.
If three No.21 chromosomes are present, Down syndrome
confirmed.
89. The risk for mothers less than 25 years of age to have the
trisomy is about 1 in 1500 births.
At 40 years of age, 1 in 100 births
At 45 years 1 in 40 births.
90. Other Syndromes
Chromosome Nomenclature: 47, +13
Chromosome formula: 2n+1
Clinical Syndrome: Trisomy-13
Estimated Frequency Birth: 1/20,000
Main Phenotypic Characteristics:
Mental deficiency and deafness, minor muscle seizures, cleft
lip, cardiac anomalies
91. Other Syndromes
Chromosome Nomenclature: 47, +18
Chromosome formula: 2n+1
Clinical Syndrome: Trisomy-18
Estimated Frequency Birth: 1/8,000
Main Phenotypic Characteristics:
Multiple congenital malformation of many organs,
malformed ears, small mouth and nose with general elfin
appearance.
90% die in the first 6 months.
92. Other Syndromes
Chromosome Nomenclature: 45, X
Chromosome formula: 2n - 1
Clinical Syndrome: Turner
Estimated Frequency Birth: 1/2,500 female
Main Phenotypic Characteristics:
Female with retarded sexual development, usually sterile,
short stature, webbing of skin in neck region, cardiovascular
abnormalities, hearing impairment.
93. Other Syndromes
Chromosome Nomenclature: 47, XXY, 48,
XXXY, 48,XXYY, 49,
XXXXY, 50, XXXXXY
Chromosome formula: 2n+1; 2n+2; 2n+2; 2n+3;
2n+4
Clinical Syndrome: Klinefelter
Estimated Frequency Birth: 1/500 male borth
Main Phenotypic Characteristics:
Pitched voice, Male, subfertile with small
testes, developed breasts, feminine, long
limbs.
94. Found in certain tissues
e.g., salivary glands of
larvae, gut epithelium,
Malphigian tubules and
some fat bodies, of some
Diptera (Drosophila,
Sciara, Rhyncosciara)
These chromosomes are
very long and thick (upto
200 times their size during
mitotic metaphase in the
case of Drosophila)
Hence they are known as
Giant chromosomesGiant chromosomes
95. They are first discovered by Balbiani in 1881 in dipteran
salivary glands and thus also known as salivary gland
chromosomes.
But their significance was realized only after the extensive
studies by Painter during 1930’s.
Giant chromosomes have also been discovered in suspensors
of young embryos of many plants, but these do not show the
bands so typical of salivary gland chromosomes.
96. He described the morphology in detail and discovered the
relation between salivary gland chromosomes and germ
cell chromosomes.
Slides of Drosophila giant chromosomes are prepared by
squashing in acetocarmine the salivary glands dissected
out from the larvae.
The total length of D.melanogater giant chromosomes is
about 2,000µ.
97. Giant chromosomes are made
up of several dark staining
regions called “bands”.
It can be separated by relatively
light or non-staining “interband”
regions.
The bands in Drosophila giant
chromosome are visible even
without staining, but after
staining they become very sharp
and clear.
In Drosophila about 5000 bands
can be recognized.
98. Some of these bands are as
thick as 0.5µ, while some may
be only 0.05µ thick.
About 25,000 base-pairs are
now estimated for each
band.
All the available evidence
clearly shows that each giant
chromosome is composed of
numerous strands, each
strand representing one
chromatid.
Therefore, these
chromosomes are also known
as “Polytene chromosome”,
and the condition is referred
to as “Polytene”
99. The numerous strands of these chromosomes are produced due
to repeated replication of the paired chromosomes without any
nuclear or cell division.
So that the number of strands (chromatids) in a chromosome
doubles after every round of DNA replication
It is estimated that giant chromosomes of Drosophila have about
1,024 strands
In the case of Chironomous may have about 4,096 strands.
The bands of giant chromosomes are formed as a result of
stacking over one another of the chromomeres of all strands
present in them.
100. Since chromatin fibers are highly coiled in chromosomes, they
stain deeply.
On the other hand, the chromatin fibers in the interband
regions are fully extended, as a result these regions take up
very light stain.
In Drosophila the location of many genes is correlated with
specific bands in the connected chromosomes.
In interband region do not have atleast functional genes
101. During certain stages of development, specific bands and
inter band regions are associated with them greatly increase
in diameter and produced a structure called Puffs or Balbiani
rings.
Puffs are believed to be produced due to uncoiling of
chromatin fibers present in the concerned chromomeres.
The puffs are sites of active RNA synthesis.
104. Lampbrush Chromosome
It was given this name because it is similar in
appearance to the brushes used to clean
lamp chimneys in centuries past.
First observed by Flemming in 1882.
The name lampbrush was given by Ruckert in
1892.
These are found in oocytic nuclei of
vertebrates (sharks, amphibians, reptiles and
birds)as well as in invertebrates (Sagitta,
sepia, Ehinaster and several species of
insects).
Also found in plants – but most experiments in
oocytes.
105. Lampbrush chromosomes are up to 800 µm
long; thus they provide very favorable
material for cytological studies.
The homologous chromosomes are paired
and each has duplicated to produce two
chromatids at the lampbrush stage.
Each lampbrush chromosome contains a
central axial region, where the two
chromatids are highly condensed
Each chromosome has several
chromomeres distributed over its length.
From each chromomere, a pair of loops
emerges in the opposite directions vertical
to the main chromosomal axis.
106. One loop represent one
chromatid, i.e., one DNA
molecule.
The size of the loop may be
ranging the average of 9.5 µm
to about 200 µm
The pairs of loops are
produced due to uncoiling of
the two chromatin fibers
present in a highly coiled state
in the chromomeres.
107. One end of each loop is thinner (thin end) than
the other end (thick end).
There is extensive RNA synthesis at the thin end of
the loops, while there is little or no RNA synthesis
at the thick end.
109. Dosage Compensation
Sex Chromosomes: females XX, males XY
Females have two copies of every X-linked gene;
males have only one.
How is this difference in gene dosage
compensated for? OR
How to create equal amount of X chromosome
gene products in males and females?
110. Levels of enzymes or proteins encoded by genes
on the X chromosome are the same in both males
and females
Even though males have 1 X chromosome and
females have 2.
111. G6PD, glucose 6 phosphate dehydrogenase,
gene is carried on the X chromosome
This gene codes for an enzyme that breaks down
sugar
Females produce the same amount of G6PD
enzyme as males
XXY and XXX individuals produce the same about
of G6PD as anyone else
112. In cells with more than two X chromosomes, only
one X remains genetically active and all the
others become inactivated.
In some cells the paternal allele is expressed
In other cells the maternal allele is expressed
In XXX and XXXX females and XXY males only 1 X
is activated in any given cell the rest are
inactivated
113.
114. Barr Bodies
1940’s two Canadian scientists noticed a dark staining mass in
the nuclei of cat brain cells
Found these dark staining spots in female but not males
This held for cats and humans
They thought the spot was a tightly condensed X chromosome
115. Barr bodies represent the inactive X chromosome and
are normally found only in female somatic cells.
Barr Bodies
116. A woman with the
chromosome
constitution 47,
XXX should have 2
Barr bodies in each
cell.
XXY individuals
are male, but have a
Barr body.
XO individuals
are female but have
no Barr bodies.
117. Which chromosome is inactive is a matter of
chance, but once an X has become inactivated ,
all cells arising from that cell will keep the same
inactive X chromosome.
In the mouse, the inactivation apparently occurs
in early in development
In human embryos, sex chromatin bodies have
been observed by the 16th
day of gestation.
118. Mechanism of X-chromosome
Inactivation
A region of the p arm of the X chromosome near
the centromere called the X-inactivation center
(XIC) is the control unit.
This region contains the gene for X-inactive
specific transcript (XIST). This RNA presumably
coats the X chromosome that expresses it and
then DNA methylation locks the chromosome in
the inactive state.
119. This occurs about 16 days after
fertilization in a female embryo.
The process is independent from
cell to cell.
A maternal or paternal X is
randomly chosen to be inactivated.
120. Rollin Hotchkiss first discovered methylated DNA in 1948.
He found that DNA from certain sources contained, in addition to
the standard four bases, a fifth: 5-methyl cytosine.
It took almost three decades to find a role for it.
In the mid-1970s, Harold Weintraub and his colleagues noticed
that active genes are low in methyl groups or under methylated.
Therefore, a relationship between under methylation and gene
activity seemed likely, as if methylation helped repress genes.
121.
122. This would be a valuable means of keeping genes inactive if
methylation passed on from parent to daughter cells during cell
division.
Each parental strand retains its methyl groups, which serve as
signals to the methylating apparatus to place methyl groups on
the newly made progeny strand.
Thus methylation has two of the requirements for mechanism of
determination:
1. It represses gene activity
2. It is permanent.
123. Strictly speaking, the DNA is altered, since methyl groups are
attached, but because methyl cytosine behaves the same as
ordinary cytosine, the genetic coding remain same.
A striking example of such a role of methylation is seen in the
inactivation of the X chromosome in female mammal.
The inactive X chromosome become heterochromatic and
appears as a dark fleck under the microscope – this
chromosome said to be lyonized, in honor of Mary Lyon who
first postulated the effect in mice.
124. An obvious explanation is that the DNA in the lyonized X
chromosome is methylated, where as the DNA in the active, X
chromosome is not.
To check this hypothesis Peter Jones and Lawrence Shapiro grew
cells in the presence of drug 5-azacytosine, which prevents DNA
methylation.
This reactivated the lyonized the X chromosome.
Furthermore, Shapiro showed these reactivated chromosomes
could be transferred to other cells and still remain active.
125.
126. Reading assignment
Grewal and Moazed (2003) “Heterochromatin
and epigenetic control of gene expression”
Science 301:798
Goldmit and Bergman (2004) “Monoallelic gene
expression: a repertoire of recurrent themes”
Immunol Rev 200:197