Linkage/class 12 biology
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linkage ppt slide is made for those learners which are a very weak understanding of the linkage concept. so it helps the students to take a clear concept from it.
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linkage
This document provides an overview of linkage in genetics. It discusses how Sutton and Boveri proposed the chromosomal theory of inheritance, where genes located on the same chromosome tend to be inherited together. It then summarizes Bateson and Punnett's pioneering experiments in 1906 that first discovered linkage between genes controlling flower color and pollen shape in sweet peas. The document outlines different phases and types of linkage, how linkage can be detected through test crosses, and the significance of linkage for plant breeding and genetics research.
Interference
1. Interference in genetics means that one crossover event on a chromosome can reduce the likelihood of another crossover event occurring near the same location.
2. The document defines interference and provides examples of positive and negative interference. Positive interference occurs when the first crossover reduces the chances of a second nearby crossover, while negative interference enhances the chances of a second nearby crossover.
3. An example calculation is shown to determine gene order, distance, and coefficient of coincidence from offspring genotypes, leading to a value of 0.17 for interference, indicating that crossover events are not independent and one reduces the chances of another nearby.
Linkage and crossing over
Linkage and crossing over,types of linkage,complete linkage,incomplete linkage,Types of crossing over
Recombination model and cytological basis of crossing over
This study evaluated the effect of expressing multiple heterologous recombinases on increasing homologous recombination in tobacco plants. The recombinases RecA, RecG, RuvC, Rad51, Rad52 and DMC1 were expressed individually and in combinations in tobacco plants containing a recombination substrate. Expression of DMC1 alone produced the greatest stimulation of homologous recombination, increasing recombination frequency up to 1000-fold. Expression of other recombinases also increased recombination 2 to 380-fold. Increasing homologous recombination could improve the efficiency of gene targeting for plant biotechnology applications using CRISPR/Cas.
Cytoplasmic inheritance
This document discusses Mendelian and non-Mendelian inheritance. It provides examples of cytoplasmic inheritance including the inheritance of chloroplast genes in Mirabilis jalapa, where the phenotype is determined by the genotype of the female parent through cytoplasmic/plastid transmission, not the genes in the nucleus. It also discusses inheritance involving cytoplasmic particles like kappa particles in Paramecium, which are transmitted maternally but whose production is controlled by nuclear genes. The key differences between Mendelian and non-Mendelian inheritance are summarized in a table.
Test Cross & Back cross
A test cross is performed to determine the genotype of a plant with dominant expression by crossing it with a recessive plant. A backcross involves breeding an F1 hybrid with one of its parents. A test cross identifies if a dominant phenotype is homozygous or heterozygous, while a backcross recovers the elite genotype of the parent and produces offspring genetically closer to the F1 hybrid's parents.
LINKAGE
GENETICS
CYTOGENETICS
Definition of Linkage, Coupling and Repulsion hypothesis, Linkage group- Drosophila, maize and man, Types of linkage-complete linkage and incomplete linkage, Factors affecting linkage- distance between genes, age, temperature, radiation, sex, chemicals and nutrition, Significance of linkage.
The tendency of two or more genes to stay together (i.e., the co-existence of two or more genes) in the same chromosome during inheritance is known as LINKAGE. The linked genes are present on the same chromosome are said to be SYNTENIC. The linked genes do not show independent assortment.
LINKAGE v/s INDEPENDENT ASSORTMENT
The frequency of linkage or the strength recombination is influenced by several factors (agents).
Maternal inheritance of chloroplasts dna
This document summarizes maternal inheritance of chloroplast DNA. It discusses how chloroplasts are inherited in the variegated four o' clock plant Mirabilis jalapa. Flowers on green branches produce only green offspring, while flowers on white branches produce only white offspring, demonstrating maternal inheritance of chloroplasts. Flowers on variegated branches produce offspring with mixed phenotypes, due to segregation of chloroplast types in the egg cell cytoplasm. This cytoplasmic inheritance demonstrates that in some plants, chloroplast DNA is inherited maternally rather than paternally.
Recommended
linkage
This document provides an overview of linkage in genetics. It discusses how Sutton and Boveri proposed the chromosomal theory of inheritance, where genes located on the same chromosome tend to be inherited together. It then summarizes Bateson and Punnett's pioneering experiments in 1906 that first discovered linkage between genes controlling flower color and pollen shape in sweet peas. The document outlines different phases and types of linkage, how linkage can be detected through test crosses, and the significance of linkage for plant breeding and genetics research.
Interference
1. Interference in genetics means that one crossover event on a chromosome can reduce the likelihood of another crossover event occurring near the same location.
2. The document defines interference and provides examples of positive and negative interference. Positive interference occurs when the first crossover reduces the chances of a second nearby crossover, while negative interference enhances the chances of a second nearby crossover.
3. An example calculation is shown to determine gene order, distance, and coefficient of coincidence from offspring genotypes, leading to a value of 0.17 for interference, indicating that crossover events are not independent and one reduces the chances of another nearby.
Linkage and crossing over
Linkage and crossing over,types of linkage,complete linkage,incomplete linkage,Types of crossing over
Recombination model and cytological basis of crossing over
This study evaluated the effect of expressing multiple heterologous recombinases on increasing homologous recombination in tobacco plants. The recombinases RecA, RecG, RuvC, Rad51, Rad52 and DMC1 were expressed individually and in combinations in tobacco plants containing a recombination substrate. Expression of DMC1 alone produced the greatest stimulation of homologous recombination, increasing recombination frequency up to 1000-fold. Expression of other recombinases also increased recombination 2 to 380-fold. Increasing homologous recombination could improve the efficiency of gene targeting for plant biotechnology applications using CRISPR/Cas.
Cytoplasmic inheritance
This document discusses Mendelian and non-Mendelian inheritance. It provides examples of cytoplasmic inheritance including the inheritance of chloroplast genes in Mirabilis jalapa, where the phenotype is determined by the genotype of the female parent through cytoplasmic/plastid transmission, not the genes in the nucleus. It also discusses inheritance involving cytoplasmic particles like kappa particles in Paramecium, which are transmitted maternally but whose production is controlled by nuclear genes. The key differences between Mendelian and non-Mendelian inheritance are summarized in a table.
Test Cross & Back cross
A test cross is performed to determine the genotype of a plant with dominant expression by crossing it with a recessive plant. A backcross involves breeding an F1 hybrid with one of its parents. A test cross identifies if a dominant phenotype is homozygous or heterozygous, while a backcross recovers the elite genotype of the parent and produces offspring genetically closer to the F1 hybrid's parents.
LINKAGE
GENETICS
CYTOGENETICS
Definition of Linkage, Coupling and Repulsion hypothesis, Linkage group- Drosophila, maize and man, Types of linkage-complete linkage and incomplete linkage, Factors affecting linkage- distance between genes, age, temperature, radiation, sex, chemicals and nutrition, Significance of linkage.
The tendency of two or more genes to stay together (i.e., the co-existence of two or more genes) in the same chromosome during inheritance is known as LINKAGE. The linked genes are present on the same chromosome are said to be SYNTENIC. The linked genes do not show independent assortment.
LINKAGE v/s INDEPENDENT ASSORTMENT
The frequency of linkage or the strength recombination is influenced by several factors (agents).
Maternal inheritance of chloroplasts dna
This document summarizes maternal inheritance of chloroplast DNA. It discusses how chloroplasts are inherited in the variegated four o' clock plant Mirabilis jalapa. Flowers on green branches produce only green offspring, while flowers on white branches produce only white offspring, demonstrating maternal inheritance of chloroplasts. Flowers on variegated branches produce offspring with mixed phenotypes, due to segregation of chloroplast types in the egg cell cytoplasm. This cytoplasmic inheritance demonstrates that in some plants, chloroplast DNA is inherited maternally rather than paternally.
Difference between genetic linkage and physical map
This document discusses genome mapping and its importance. Genome mapping involves determining the locations of genes on chromosomes. Gene mapping is important for understanding genetic diseases and identifying defective genes. There are two main types of mapping - linkage mapping and physical mapping. Linkage mapping determines the relative distances between genes based on recombination frequency during meiosis, while physical mapping identifies the exact locations of genes on chromosomes. Genome mapping is a useful tool that has mapped many plant genomes like rice, maize, and wheat.
linkage.pptx
Boyd 2014 [16] Record linkage is the process of bringing together data relating to the same individual from within and between different datasets. When a unique person-based identifier exists, linkage can be achieved by simply merging datasets on the identifier.
Linkage is the close association of genes or other DNA sequences on the same chromosome. The closer two genes are to each other on the chromosome, the greater the probability that they will be inherited together.
The two different types of linkage are:
Complete linkage.
Incomplete linkage.
“Linkage and recombination are the phenomena that describe the inheritance of genes.”
Cytological proof for crossing over
Curt Stern provided the first cytological evidence of genetic crossing over in 1931 through experiments with Drosophila. He used a female fly with two distinct X chromosomes - one normal and one broken into segments. These chromosomes contained different alleles for eye color and shape. His analysis of offspring from crosses showed recombinant chromosome types could only arise through exchange of segments between homologous non-sister chromatids, proving that genetic crossing over involves an actual exchange of chromosome segments. Similar results were later found in maize by Creighton and McClintock, firmly establishing the cytological basis of genetic recombination.
EXTRA CHROMOSOMAL INHERITANCE
Extrachromosomal inheritance involves the transmission of genetic traits from parent to offspring through cytoplasmic organelles like chloroplasts and mitochondria, rather than through nuclear genes. Three examples are given: (1) variegated leaves in four o'clock plants are inherited cytoplasmically, (2) streptomycin resistance in Chlamydomonas is inherited through chloroplasts, and (3) "poky" phenotype and abnormal cytochromes in Neurospora are inherited maternally through mitochondria. Cytoplasmic inheritance can also cause traits like cytoplasmic male sterility in plants. Maternal effects occur when the female parent's genotype influences offspring traits regardless of the male parent's genotype.
2. Gene interaction - complementary
Basics of Undergraduate/university fellows
Complementation between two non-allelic genes (C and P) are essential for production
of a particular or special phenotype i.e., complementary factor.
Two genes involved in a specific pathway and their functional products are required
for gene expression, then one recessive allelic pair at either allelic pair would result in
the mutant phenotype.
When Dominant alleles are present together, they complement each other to yield
complementary factor resulting in a special phenotype.
They are called complementary genes.
When either of gene loci have homozygous recessive alleles (i.e., genotypes of ccPP,
ccPp, CCpp, Ccpp and ccpp), they produce identical phenotypes and change F2 ratio
to 9:7.
Penetrance and expressivity.pdf
Penetrance and expressivity refer to how likely and how strongly, respectively, a genetic trait is expressed in individuals. Penetrance is the proportion of individuals with a genotype who exhibit the associated phenotype, ranging from complete (100%) to incomplete. Expressivity refers to how strongly or uniformly a phenotype is manifested across an individual's body. A phenocopy is an environmentally induced phenotype that resembles a genetically determined trait but is not inherited. Diabetes has an incompletely penetrant genetic basis but treating it with insulin produces a phenocopy of the non-diabetic phenotype.
Structural and numerical chromosomal abberations
This document provides an overview of structural and numerical chromosomal aberrations. It begins by defining chromosomal aberrations and describing the main types: structural (deletions, duplications, inversions, translocations) and numerical (aneuploidy, euploidy). For each type of aberration, the document discusses their origin, effects, and significance in crop improvement. Case studies are also presented to illustrate concepts like detecting deletions in Drosophila and producing monosomics in wheat. The document concludes by emphasizing the use of chromosomal aberrations in genetic mapping and breeding new crop varieties.
CYTOPLASMIC INHERITANCE
Contents
Introduction
Mitochondrial or maternal inheritance
Shell coiling in Snail(Limnaea pregra)
Plastidial or chloroplast inheritance
Leaf variegation in Mirabilis Jalapa
Inheritance Involving Infective Particles
Kappa particles in Paramecium
Signififcance
References
Numerical changes in chromosome
This document defines and describes various types of numerical changes in chromosomes, including euploidy, aneuploidy, polyploidy, and autopolyploidy vs allopolyploidy. It provides examples of polyploidy levels from haploidy to hexaploidy. It also discusses aneuploidy conditions including monosomy, nullisomy, trisomy, tetrasomy, pentasomy, hexasomy, and heptasomy. The key differences between autopolyploidy and allopolyploidy are that autopolyploidy involves multiple copies of chromosomes from the same species, while allopolyploidy involves chromosomes from different species.
Role of B chromosome in plants
B chromosomes are extra chromosomes found in some species in addition to the standard chromosome number. They are smaller than normal chromosomes and do not follow Mendelian inheritance. B chromosomes have been found to affect traits like growth, flowering time, and fertility in some plant species. Their presence can influence genetic recombination and variability by impacting chiasma formation and chromosome pairing at meiosis. While many effects of B chromosomes are detrimental, their ability to increase genetic variation could provide an adaptive advantage in generating new genotypes.
linkage and crossing over
This document discusses linkage and crossing over of genes. It explains that genes located on the same chromosome are linked, and the closer they are, the stronger the linkage. Crossing over occurs during meiosis and leads to recombination of genes from homologous chromosomes. Linkage maps can be constructed by observing the frequency of crossing over between linked gene loci. These maps show the linear order and genetic distances between genes on chromosomes.
Apomixis
Apomixis, Types of Apomixis, Mechanism, Sporophytic and Gametophytic Apomixis, Source and Impact of Apomixis, Identification of Apomixis
Crossing over
Crossing over refers to the exchange of genetic material between non-sister chromatids of homologous chromosomes during meiosis. It results in new combinations of genes and genetic variation. Crossing over occurs via the formation of chiasmata, where segments are exchanged between chromatids. It can involve two, three, or all four chromatids, and can be single, double, or multiple. Factors like temperature, radiation, age, and nutrition can influence the rate of crossing over. Its significance includes providing evidence for gene order and creating genetic variation important for breeding programs.
Presentation on Evolution of Raphanobrassica
This document summarizes the process of allopolyploidy in crop species evolution. It discusses how allopolyploids contain chromosomes from two or more different species and can occur naturally or be experimentally produced. A key example provided is the origin of Raphanobrassica, an allotetraploid produced by crossing Raphanus sativus (radish) and Brassica oleracea (cabbage). While the initial hybrid was sterile, chromosome doubling resulted in a fertile allotetraploid with 36 chromosomes that exhibited traits of both parent species. The document notes how allopolyploidization has contributed to the evolution of important crop species like wheat, cotton and tobacco.
Mendel's law
The document summarizes Mendel's laws of inheritance based on his experiments with pea plants. It discusses Mendel's discovery of the laws of dominance, segregation, and independent assortment through monohybrid and dihybrid crosses. The law of dominance states that one trait will mask the other in hybrid offspring. The law of segregation explains that alleles separate during gamete formation so each gamete contains one allele. The law of independent assortment says that allele pairs assort independently, resulting in multiple allele combinations in offspring. Mendel's laws explained inheritance of traits for the first time.
10.3 polygenic inheritance
Polygenic inheritance involves multiple genes contributing to a trait, as opposed to single-gene inheritance. It can result in continuous variation, where a wide range of phenotypes exist between extremes. Human skin color and wheat seed color are examples of polygenic traits that show continuous variation, with skin color determined by 3-4 genes influencing melanin production and seed color by 3 genes determining red pigment levels.
Complementation test
In this presentation, I'll try to explain the complementation test. This test is important for assessment of functional allelism.
Pleiotropy
This PPT consists of 15 slides only explaining Pleiotropy. This is a phenomenon when one gene controls more than one trait , the traits may be related .Generally one gene's product acts for many reactions and so can affect more than one trait. Examples can be seen in pea Coloured flower and pigmentation in leaf axil, frizzle trait in chicken, fur colour and deafness in cats,Human pleiotropic traits are PKU,Sickle cell Anaemia. HOsyndrome , p53 gene etc
Back cross and test cross
Backcrossing involves crossing a hybrid with one of its parents to produce offspring that are genetically more similar to the parent. It is used in plant and animal breeding to transfer desired traits from a hybrid back into a parent's genetic background. A backcross can be described as BC1, BC2, etc depending on how many times the hybrid has been backcrossed. Backcrossing with the dominant parent will result in all dominant phenotype offspring, while backcrossing with the recessive parent will result in a 1:1 phenotypic ratio.
Linkage
- Linkage refers to the tendency of genes located near each other on the same chromosome to be inherited together during meiosis. This is because genes located close together on a chromosome move together to the same pole during cell division.
- There are different types of linkage based on whether crossing over occurs, the genes involved, and the chromosomes. Linkage can be complete or incomplete depending on the presence or absence of crossing over. It can involve dominant or recessive alleles.
- Linkage is detected through test crosses, where deviations from expected Mendelian ratios indicate genes are linked. The strength of linkage depends on distance between genes, with closer genes showing stronger linkage.
linkage.pptx
Gene which are located on the same chromosome and are transmitted together in the offsprings are called linked genes. This phenomenon of inheritance of linked genes together so as to retain the parental combinations in the offsprings is known as linkage.
The characters controlled by linked genes are called linked characters.
All those which located in a single chromosome constitute a linked group.
Linkage – concept, types and theories
1. Genetic linkage occurs when two genes located near each other on the same chromosome tend to be inherited together during meiosis.
2. Early theories of linkage proposed by Sutton, Boveri, Bateson and Punnett failed to fully explain observed inheritance patterns.
3. Morgan's chromosomal theory of linkage established that genes are linearly arranged on chromosomes and that the closer two genes are, the stronger the tendency for them to be inherited together. This provided an explanation for linkage patterns and laid the foundation for modern genetics.
More Related Content
What's hot
Difference between genetic linkage and physical map
This document discusses genome mapping and its importance. Genome mapping involves determining the locations of genes on chromosomes. Gene mapping is important for understanding genetic diseases and identifying defective genes. There are two main types of mapping - linkage mapping and physical mapping. Linkage mapping determines the relative distances between genes based on recombination frequency during meiosis, while physical mapping identifies the exact locations of genes on chromosomes. Genome mapping is a useful tool that has mapped many plant genomes like rice, maize, and wheat.
linkage.pptx
Boyd 2014 [16] Record linkage is the process of bringing together data relating to the same individual from within and between different datasets. When a unique person-based identifier exists, linkage can be achieved by simply merging datasets on the identifier.
Linkage is the close association of genes or other DNA sequences on the same chromosome. The closer two genes are to each other on the chromosome, the greater the probability that they will be inherited together.
The two different types of linkage are:
Complete linkage.
Incomplete linkage.
“Linkage and recombination are the phenomena that describe the inheritance of genes.”
Cytological proof for crossing over
Curt Stern provided the first cytological evidence of genetic crossing over in 1931 through experiments with Drosophila. He used a female fly with two distinct X chromosomes - one normal and one broken into segments. These chromosomes contained different alleles for eye color and shape. His analysis of offspring from crosses showed recombinant chromosome types could only arise through exchange of segments between homologous non-sister chromatids, proving that genetic crossing over involves an actual exchange of chromosome segments. Similar results were later found in maize by Creighton and McClintock, firmly establishing the cytological basis of genetic recombination.
EXTRA CHROMOSOMAL INHERITANCE
Extrachromosomal inheritance involves the transmission of genetic traits from parent to offspring through cytoplasmic organelles like chloroplasts and mitochondria, rather than through nuclear genes. Three examples are given: (1) variegated leaves in four o'clock plants are inherited cytoplasmically, (2) streptomycin resistance in Chlamydomonas is inherited through chloroplasts, and (3) "poky" phenotype and abnormal cytochromes in Neurospora are inherited maternally through mitochondria. Cytoplasmic inheritance can also cause traits like cytoplasmic male sterility in plants. Maternal effects occur when the female parent's genotype influences offspring traits regardless of the male parent's genotype.
2. Gene interaction - complementary
Basics of Undergraduate/university fellows
Complementation between two non-allelic genes (C and P) are essential for production
of a particular or special phenotype i.e., complementary factor.
Two genes involved in a specific pathway and their functional products are required
for gene expression, then one recessive allelic pair at either allelic pair would result in
the mutant phenotype.
When Dominant alleles are present together, they complement each other to yield
complementary factor resulting in a special phenotype.
They are called complementary genes.
When either of gene loci have homozygous recessive alleles (i.e., genotypes of ccPP,
ccPp, CCpp, Ccpp and ccpp), they produce identical phenotypes and change F2 ratio
to 9:7.
Penetrance and expressivity.pdf
Penetrance and expressivity refer to how likely and how strongly, respectively, a genetic trait is expressed in individuals. Penetrance is the proportion of individuals with a genotype who exhibit the associated phenotype, ranging from complete (100%) to incomplete. Expressivity refers to how strongly or uniformly a phenotype is manifested across an individual's body. A phenocopy is an environmentally induced phenotype that resembles a genetically determined trait but is not inherited. Diabetes has an incompletely penetrant genetic basis but treating it with insulin produces a phenocopy of the non-diabetic phenotype.
Structural and numerical chromosomal abberations
This document provides an overview of structural and numerical chromosomal aberrations. It begins by defining chromosomal aberrations and describing the main types: structural (deletions, duplications, inversions, translocations) and numerical (aneuploidy, euploidy). For each type of aberration, the document discusses their origin, effects, and significance in crop improvement. Case studies are also presented to illustrate concepts like detecting deletions in Drosophila and producing monosomics in wheat. The document concludes by emphasizing the use of chromosomal aberrations in genetic mapping and breeding new crop varieties.
CYTOPLASMIC INHERITANCE
Contents
Introduction
Mitochondrial or maternal inheritance
Shell coiling in Snail(Limnaea pregra)
Plastidial or chloroplast inheritance
Leaf variegation in Mirabilis Jalapa
Inheritance Involving Infective Particles
Kappa particles in Paramecium
Signififcance
References
Numerical changes in chromosome
This document defines and describes various types of numerical changes in chromosomes, including euploidy, aneuploidy, polyploidy, and autopolyploidy vs allopolyploidy. It provides examples of polyploidy levels from haploidy to hexaploidy. It also discusses aneuploidy conditions including monosomy, nullisomy, trisomy, tetrasomy, pentasomy, hexasomy, and heptasomy. The key differences between autopolyploidy and allopolyploidy are that autopolyploidy involves multiple copies of chromosomes from the same species, while allopolyploidy involves chromosomes from different species.
Role of B chromosome in plants
B chromosomes are extra chromosomes found in some species in addition to the standard chromosome number. They are smaller than normal chromosomes and do not follow Mendelian inheritance. B chromosomes have been found to affect traits like growth, flowering time, and fertility in some plant species. Their presence can influence genetic recombination and variability by impacting chiasma formation and chromosome pairing at meiosis. While many effects of B chromosomes are detrimental, their ability to increase genetic variation could provide an adaptive advantage in generating new genotypes.
linkage and crossing over
This document discusses linkage and crossing over of genes. It explains that genes located on the same chromosome are linked, and the closer they are, the stronger the linkage. Crossing over occurs during meiosis and leads to recombination of genes from homologous chromosomes. Linkage maps can be constructed by observing the frequency of crossing over between linked gene loci. These maps show the linear order and genetic distances between genes on chromosomes.
Apomixis
Apomixis, Types of Apomixis, Mechanism, Sporophytic and Gametophytic Apomixis, Source and Impact of Apomixis, Identification of Apomixis
Crossing over
Crossing over refers to the exchange of genetic material between non-sister chromatids of homologous chromosomes during meiosis. It results in new combinations of genes and genetic variation. Crossing over occurs via the formation of chiasmata, where segments are exchanged between chromatids. It can involve two, three, or all four chromatids, and can be single, double, or multiple. Factors like temperature, radiation, age, and nutrition can influence the rate of crossing over. Its significance includes providing evidence for gene order and creating genetic variation important for breeding programs.
Presentation on Evolution of Raphanobrassica
This document summarizes the process of allopolyploidy in crop species evolution. It discusses how allopolyploids contain chromosomes from two or more different species and can occur naturally or be experimentally produced. A key example provided is the origin of Raphanobrassica, an allotetraploid produced by crossing Raphanus sativus (radish) and Brassica oleracea (cabbage). While the initial hybrid was sterile, chromosome doubling resulted in a fertile allotetraploid with 36 chromosomes that exhibited traits of both parent species. The document notes how allopolyploidization has contributed to the evolution of important crop species like wheat, cotton and tobacco.
Mendel's law
The document summarizes Mendel's laws of inheritance based on his experiments with pea plants. It discusses Mendel's discovery of the laws of dominance, segregation, and independent assortment through monohybrid and dihybrid crosses. The law of dominance states that one trait will mask the other in hybrid offspring. The law of segregation explains that alleles separate during gamete formation so each gamete contains one allele. The law of independent assortment says that allele pairs assort independently, resulting in multiple allele combinations in offspring. Mendel's laws explained inheritance of traits for the first time.
10.3 polygenic inheritance
Polygenic inheritance involves multiple genes contributing to a trait, as opposed to single-gene inheritance. It can result in continuous variation, where a wide range of phenotypes exist between extremes. Human skin color and wheat seed color are examples of polygenic traits that show continuous variation, with skin color determined by 3-4 genes influencing melanin production and seed color by 3 genes determining red pigment levels.
Complementation test
In this presentation, I'll try to explain the complementation test. This test is important for assessment of functional allelism.
Pleiotropy
This PPT consists of 15 slides only explaining Pleiotropy. This is a phenomenon when one gene controls more than one trait , the traits may be related .Generally one gene's product acts for many reactions and so can affect more than one trait. Examples can be seen in pea Coloured flower and pigmentation in leaf axil, frizzle trait in chicken, fur colour and deafness in cats,Human pleiotropic traits are PKU,Sickle cell Anaemia. HOsyndrome , p53 gene etc
Back cross and test cross
Backcrossing involves crossing a hybrid with one of its parents to produce offspring that are genetically more similar to the parent. It is used in plant and animal breeding to transfer desired traits from a hybrid back into a parent's genetic background. A backcross can be described as BC1, BC2, etc depending on how many times the hybrid has been backcrossed. Backcrossing with the dominant parent will result in all dominant phenotype offspring, while backcrossing with the recessive parent will result in a 1:1 phenotypic ratio.
Linkage
- Linkage refers to the tendency of genes located near each other on the same chromosome to be inherited together during meiosis. This is because genes located close together on a chromosome move together to the same pole during cell division.
- There are different types of linkage based on whether crossing over occurs, the genes involved, and the chromosomes. Linkage can be complete or incomplete depending on the presence or absence of crossing over. It can involve dominant or recessive alleles.
- Linkage is detected through test crosses, where deviations from expected Mendelian ratios indicate genes are linked. The strength of linkage depends on distance between genes, with closer genes showing stronger linkage.
What's hot (20)
Difference between genetic linkage and physical map
Difference between genetic linkage and physical map
Similar to Linkage/class 12 biology
linkage.pptx
Gene which are located on the same chromosome and are transmitted together in the offsprings are called linked genes. This phenomenon of inheritance of linked genes together so as to retain the parental combinations in the offsprings is known as linkage.
The characters controlled by linked genes are called linked characters.
All those which located in a single chromosome constitute a linked group.
Linkage – concept, types and theories
1. Genetic linkage occurs when two genes located near each other on the same chromosome tend to be inherited together during meiosis.
2. Early theories of linkage proposed by Sutton, Boveri, Bateson and Punnett failed to fully explain observed inheritance patterns.
3. Morgan's chromosomal theory of linkage established that genes are linearly arranged on chromosomes and that the closer two genes are, the stronger the tendency for them to be inherited together. This provided an explanation for linkage patterns and laid the foundation for modern genetics.
Linkage and crossing over
1. Linkage occurs when genes located on the same chromosome fail to assort independently during meiosis. This causes traits to be inherited together in offspring.
2. Bateson and Punnett first reported linkage in 1906 while studying flower color and pollen shape in peas. They observed a deviation from expected Mendelian ratios, indicating linkage between the genes.
3. Morgan's studies of fruit flies provided the first evidence that linkage is due to genes being located on the same chromosome. Crossing over during meiosis can lead to new combinations of linked genes.
Linkage and Crossing over (Sanjay Chetry).pptx
Linkage
1. Linkage ensures to keep the genes in a chromosome to inherit together
2. The strength of linkage between two genes is inversely proportional to the distance between them in the chromosome
3. The strength of linkage between two genes increases with the decrease in distance between them.
4. The strength of linkage decrease with increase in distance between the genes.
5. Linkage ensures the maintenance of parental trait in the offspring.
6. Linkage reduces the chance of creation of variability with sexual reproduction.
Crossing Over
1. Crossing over facilitates the separation of genes present chromosome and segregate into different gametes.
2. The chance of crossing over between two genes is directly proportional to the distance between them in the chromosome
3. The chance of crossing over between two genes decreases with the decrease in the distance between them.
4. The chance of crossing increases with increase in distance between the genes.
5. The crossing over causes alterations in the parental traits in the offspring.
6. Crossing over increases the chance of variability with sexual reproduction.
Gene linkage.
This document discusses gene linkage, which refers to the tendency of genes located near each other on the same chromosome to be inherited together during gamete formation. It notes that chromosomes contain multiple genes arranged in linkage groups. The closer two genes are on a chromosome, the less likely they are to be separated during crossing over. The discovery of genetic linkage was made by scientists Bateson and Punnett through experiments with pea plants tracking the inheritance of flower color and shape. Their findings showed that some gene combinations were consistently inherited together, indicating linkage. There are two types of linkage: complete and incomplete, depending on whether non-parental combinations are produced. Linkage is significant as it reduces recombination of genes and helps maintain parental traits.
linkage and crossing over
This document discusses linkage and crossing over in genetics. It begins by defining linkage as genes located on the same chromosome staying together during inheritance. Linkage is discovered when genes are inherited together more often than expected by chance. Crossing over occurs when genetic material is exchanged between homologous chromosomes, allowing for new combinations of genes. The document then discusses different aspects of linkage and crossing over, including how they were discovered, characteristics, mechanisms, factors that affect them, and differences between the two concepts. It provides examples to illustrate concepts like complete versus incomplete linkage.
Linkage
Genetic linkage is the tendency of DNA sequences that are close together on a chromosome to be inherited together during the meiosis phase of sexual reproduction.
Linkage-GBR.pdf
1) Linkage refers to the tendency of genes located near each other on the same chromosome to be inherited together during meiosis. It was first reported by Bateson and Punnett in 1906 while studying traits in sweet peas.
2) There are different types of linkage based on factors like crossing over, genes involved, and chromosomes. Complete linkage occurs when genes are so close there is no crossing over, while incomplete linkage allows some crossing over. Coupling refers to dominant alleles being inherited together and recessive together.
3) Mapping gene locations based on linkage analysis helped scientists like Morgan produce the first chromosome maps and better understand inheritance patterns that violate Mendel's law of independent assortment. Linkage is an exception that
Linkage
This document discusses genetic linkage and its related concepts and theories. It defines genetic linkage as the tendency of genes located near each other on the same chromosome to be inherited together. It describes Walter Sutton's hypothesis that chromosomes carry hereditary units and Sutton and Boveri's chromosome theory of inheritance. It also discusses Bateson and Punnett's coupling and repulsion hypothesis, Morgan's discovery of gene location on chromosomes through fly experiments, and the different types of linkage like complete and incomplete linkage. Examples are provided to illustrate concepts like complete and incomplete linkage.
The most likely F1 will be the one that is made from 4 and 5. This i.pdf
The document discusses two genetic maps between genes c and d. Map 1 shows a distance of 15 between the genes, while Map 2 shows a distance of 20. Since a greater distance between genes means more recombinants, the F1 offspring from parents 4 and 5 have a greater chance of losing homozygous recessive alleles due to less linkage between genes c and d in Map 2. Therefore, the F1 from parents 4 and 5 is most likely.
Similar to Linkage/class 12 biology (10)
The most likely F1 will be the one that is made from 4 and 5. This i.pdf
The most likely F1 will be the one that is made from 4 and 5. This i.pdf
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Development of frog/ embryogenesis
1. The development of frog consists of copulation, spawning, fertilization, cleavage, blastulation, gastrulation, and post-embryonic development.
2. During gastrulation, epiboly, imboly, contraction of the blastopore, and involution occur, forming the three germ layers - ectoderm, mesoderm, and endoderm.
3. Post-embryonic development includes neurogenesis forming the neural tube, notogenesis forming the notochord, and coelom formation separating the mesoderm into three layers.
Migration in fishes/class11 biology
Migration in fishes generally refers to the periodic movement of fish from one place to another for purposes such as food, shelter, breeding, or protection. There are several types of migration including diadromous migration where fish move between freshwater and seawater for breeding, potamodromous migration within freshwater systems, and oceanodromous migration confined to ocean waters for food. Some key advantages of migration for fish are that it allows them to find safe shelter, ample food sources, better conditions for reproduction, and helps them to adapt to new environments while avoiding competition.
Description of family solanaceae in semi technical term/class11 bilogy
This document summarizes the characteristics of the Solanaceae family of plants. It describes that the family includes over 2,200 species distributed mainly in tropical and temperate regions. Most members are herbs, shrubs, or trees that have alternate leaves, cymose inflorescences, and berries or capsules as fruits. Economically important plants in this family include potatoes, tomatoes, chilies, tobacco, and belladonna, which is used to extract atropine.
Description of family fabaceae
This document summarizes the key characteristics of plants in the Fabaceae family, also known as legumes. It describes their distribution in temperate and subtropical regions. Most are annual or perennial herbs, shrubs, or trees with branched taproots containing nitrogen-fixing nodules. Their leaves are alternately arranged and compound, stems are branched, and flowers are usually racemose with five fused sepals and five fused petals. Economically, they are important as vegetables, pulses, and for their ability to fix nitrogen in soil.
Development of embryo/class12 biology
The document summarizes the development of dicot and monocot embryos. It begins by defining embryogenesis as the process after fertilization that produces a fully developed plant embryo. It then describes the development of dicot embryos, starting with the zygote dividing into two cells, one forming the suspensor and one the embryo proper. The embryo cell divides further to form the octant stage with eight cells that develop into various embryo parts. For monocot embryos, the zygote also divides into two cells but the basal cell does not divide further and forms the suspensor directly while the embryo cell divides to form the plumule, hypocotyl, and radicle.
Pollination/class 12 biology
This document discusses different types of pollination in plants. It describes self-pollination, which can occur through autogamy within a flower or geitonogamy between different flowers of the same plant. Cross-pollination involves the transfer of pollen between different plants and can be facilitated by biotic agents like insects, birds, or abiotic factors like wind and water. The document provides examples of different pollination types and notes advantages and disadvantages of self-pollination versus cross-pollination.
Floral formula and floral diagram
the floral formula tells us about the nature of flowers. the floral diagram represents the plan of arrangements of floral whorl in relation to the mother axis.
Animal behavior/ orientation/taxes
this ppt slide consists of the definition of orientation, types of taxis. these slides help students to understand taxis' behavior in an easy way.
Schon's models of curriculum dissemination
Schon identified three models of curriculum dissemination:
1. The center-periphery model involves dissemination controlled from a central source spreading outward.
2. The proliferation of centres model establishes primary and secondary centers that both support and expand dissemination.
3. The shifting- centres method emerges from social movements and lacks clearly established secondary centers, instead dissemination responds to local demands.
Analysis of new curriculum of class 11 biology/
The document analyzes and compares the new and old class 11 biology curriculum in Nepal. The new curriculum was revised based on research and suggestions to include more practical and application-based learning. It divides content into competencies, theory, and practical sections for both botany and zoology. While course content remained similar, the new curriculum reorganized some topics, increased practical hours, emphasized projects and field work, and implemented a blended assessment approach including internal and external evaluations. The goal of the revisions was to make the curriculum more conceptual, practical, and skill-based compared to the previous knowledge-based theoretical model.
Logical inference and inquiry
Logical inference and inquiry is a document about logic and logical reasoning. It discusses what logic is, including that it has two main parts - semantics and syntax. It also discusses logical inference as deriving conclusions from premises, and provides an example inference about dogs having four legs. The document outlines different rules of inference and their validity being based on form rather than truth. Finally, it discusses logical inquiry as any process aimed at increasing knowledge or solving problems, involving abductive, deductive and inductive reasoning.
Megasporogenesis/class 12 biology
it is about the megagametogenesis and development of female gametophytes. it is helpful for intermediate biology students.
Pteridophyta/ class 11 biology
This document describes the life cycle of ferns. It explains that ferns reproduce asexually through spores and sexually through gametophytes. The spores grow into heart-shaped prothalli that produce male antheridia and female archegonia for fertilization. Fertilization results in a diploid zygote that develops into a new fern sporophyte, completing the alternation of generations.
Epistasis/class 12 biology
it is about the genetic interaction, epistatic mechanism of dominant and recessive takes place in animal and plants
Environmental pollution/intermediate/campus level
this slide for biology students and helpful for intermediate and bachelor level students. students can learn about air pollution very easily. it gives a detailed description of air pollutants, their causes, and preventive measures with a clear photograph.
Chromosomal mutation/class 12 biology
this slide is about mutation especially on gene and chromosomal mutation for intermediate students. students can take benefit from it
Vegetative reproduction in angiosperm
Vegetative reproduction is a form of asexual reproduction in plants where new individuals are formed from vegetative organs like roots, stems, and leaves. There are two types of vegetative reproduction - natural, which occurs through modified roots, stems, and leaves; and artificial, where humans interfere to propagate plants through methods like layering, grafting, and tissue culture. Vegetative reproduction allows for the large scale, rapid production of identical new plants that inherit the parent's characteristics.
Sexual reproduction in angiosperm(microsporogenesis)
This document summarizes the process of microsporogenesis and microgametogenesis in angiosperms. Microsporogenesis involves the formation of microspores (pollen grains) from microspore mother cells within the anther through meiosis. The anther contains four layers surrounding the pollen sacs: epidermis, endothecium, middle layer, and tapetum. During microgametogenesis, the pollen grain germinates and its nucleus divides to form a vegetative cell and generative cell. The generative cell then divides into two sperm cells that are delivered to the female gametophyte via a pollen tube.
Animal behavior
- Animal behavior is the reaction and expression of organisms in response to external stimuli in their environment. This includes both innate, genetically determined behaviors as well as learned behaviors acquired through experience.
- Reflex actions are automatic, involuntary responses to stimuli that occur very quickly via neural pathways between receptors, the spinal cord, and effectors. An example is withdrawing one's hand from a hot object.
- The mechanism of a reflex involves stimulation of sensory receptors, conduction of impulses through sensory neurons to the spinal cord, modulation in the spinal cord, and transmission of impulses through motor neurons to effector organs to produce the reflex response.
More from Dambar Khatri (19)
Description of family solanaceae in semi technical term/class11 bilogy
Description of family solanaceae in semi technical term/class11 bilogy
Sexual reproduction in angiosperm(microsporogenesis)
Sexual reproduction in angiosperm(microsporogenesis)
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Micronuclei test.M.sc.zoology.fisheries.
Current Ms word generated power point presentation covers major details about the micronuclei test. It's significance and assays to conduct it. It is used to detect the micronuclei formation inside the cells of nearly every multicellular organism. It's formation takes place during chromosomal sepration at metaphase.
Nucleophilic Addition of carbonyl compounds.pptx
Nucleophilic addition is the most important reaction of carbonyls. Not just aldehydes and ketones, but also carboxylic acid derivatives in general.
Carbonyls undergo addition reactions with a large range of nucleophiles.
Comparing the relative basicity of the nucleophile and the product is extremely helpful in determining how reversible the addition reaction is. Reactions with Grignards and hydrides are irreversible. Reactions with weak bases like halides and carboxylates generally don’t happen.
Electronic effects (inductive effects, electron donation) have a large impact on reactivity.
Large groups adjacent to the carbonyl will slow the rate of reaction.
Neutral nucleophiles can also add to carbonyls, although their additions are generally slower and more reversible. Acid catalysis is sometimes employed to increase the rate of addition.
原版制作(carleton毕业证书)卡尔顿大学毕业证硕士文凭原版一模一样
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留信网认证的作用:
1:该专业认证可证明留学生真实身份
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What is greenhouse gasses and how many gasses are there to affect the Earth.
What are greenhouse gasses how they affect the earth and its environment what is the future of the environment and earth how the weather and the climate effects.
Sharlene Leurig - Enabling Onsite Water Use with Net Zero Water
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ESPP presentation to EU Waste Water Network, 4th June 2024 “EU policies driving nutrient removal and recycling
and the revised UWWTD (Urban Waste Water Treatment Directive)”
Randomised Optimisation Algorithms in DAPHNE
Slides from talk:
Aleš Zamuda: Randomised Optimisation Algorithms in DAPHNE .
Austrian-Slovenian HPC Meeting 2024 – ASHPC24, Seeblickhotel Grundlsee in Austria, 10–13 June 2024
https://ashpc.eu/
Unlocking the mysteries of reproduction: Exploring fecundity and gonadosomati...
The pygmy halfbeak Dermogenys colletei, is known for its viviparous nature, this presents an intriguing case of relatively low fecundity, raising questions about potential compensatory reproductive strategies employed by this species. Our study delves into the examination of fecundity and the Gonadosomatic Index (GSI) in the Pygmy Halfbeak, D. colletei (Meisner, 2001), an intriguing viviparous fish indigenous to Sarawak, Borneo. We hypothesize that the Pygmy halfbeak, D. colletei, may exhibit unique reproductive adaptations to offset its low fecundity, thus enhancing its survival and fitness. To address this, we conducted a comprehensive study utilizing 28 mature female specimens of D. colletei, carefully measuring fecundity and GSI to shed light on the reproductive adaptations of this species. Our findings reveal that D. colletei indeed exhibits low fecundity, with a mean of 16.76 ± 2.01, and a mean GSI of 12.83 ± 1.27, providing crucial insights into the reproductive mechanisms at play in this species. These results underscore the existence of unique reproductive strategies in D. colletei, enabling its adaptation and persistence in Borneo's diverse aquatic ecosystems, and call for further ecological research to elucidate these mechanisms. This study lends to a better understanding of viviparous fish in Borneo and contributes to the broader field of aquatic ecology, enhancing our knowledge of species adaptations to unique ecological challenges.
EWOCS-I: The catalog of X-ray sources in Westerlund 1 from the Extended Weste...
Context. With a mass exceeding several 104 M⊙ and a rich and dense population of massive stars, supermassive young star clusters
represent the most massive star-forming environment that is dominated by the feedback from massive stars and gravitational interactions
among stars.
Aims. In this paper we present the Extended Westerlund 1 and 2 Open Clusters Survey (EWOCS) project, which aims to investigate
the influence of the starburst environment on the formation of stars and planets, and on the evolution of both low and high mass stars.
The primary targets of this project are Westerlund 1 and 2, the closest supermassive star clusters to the Sun.
Methods. The project is based primarily on recent observations conducted with the Chandra and JWST observatories. Specifically,
the Chandra survey of Westerlund 1 consists of 36 new ACIS-I observations, nearly co-pointed, for a total exposure time of 1 Msec.
Additionally, we included 8 archival Chandra/ACIS-S observations. This paper presents the resulting catalog of X-ray sources within
and around Westerlund 1. Sources were detected by combining various existing methods, and photon extraction and source validation
were carried out using the ACIS-Extract software.
Results. The EWOCS X-ray catalog comprises 5963 validated sources out of the 9420 initially provided to ACIS-Extract, reaching a
photon flux threshold of approximately 2 × 10−8 photons cm−2
s
−1
. The X-ray sources exhibit a highly concentrated spatial distribution,
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massive stars of the cluster, and we have collected over 71 000 photons from the magnetar CXO J164710.20-455217.
ESR spectroscopy in liquid food and beverages.pptx
With increasing population, people need to rely on packaged food stuffs. Packaging of food materials requires the preservation of food. There are various methods for the treatment of food to preserve them and irradiation treatment of food is one of them. It is the most common and the most harmless method for the food preservation as it does not alter the necessary micronutrients of food materials. Although irradiated food doesn’t cause any harm to the human health but still the quality assessment of food is required to provide consumers with necessary information about the food. ESR spectroscopy is the most sophisticated way to investigate the quality of the food and the free radicals induced during the processing of the food. ESR spin trapping technique is useful for the detection of highly unstable radicals in the food. The antioxidant capability of liquid food and beverages in mainly performed by spin trapping technique.
Applied Science: Thermodynamics, Laws & Methodology.pdf
When I was asked to give a companion lecture in support of ‘The Philosophy of Science’ (https://shorturl.at/4pUXz) I decided not to walk through the detail of the many methodologies in order of use. Instead, I chose to employ a long standing, and ongoing, scientific development as an exemplar. And so, I chose the ever evolving story of Thermodynamics as a scientific investigation at its best.
Conducted over a period of >200 years, Thermodynamics R&D, and application, benefitted from the highest levels of professionalism, collaboration, and technical thoroughness. New layers of application, methodology, and practice were made possible by the progressive advance of technology. In turn, this has seen measurement and modelling accuracy continually improved at a micro and macro level.
Perhaps most importantly, Thermodynamics rapidly became a primary tool in the advance of applied science/engineering/technology, spanning micro-tech, to aerospace and cosmology. I can think of no better a story to illustrate the breadth of scientific methodologies and applications at their best.
bordetella pertussis.................................ppt
Bordettela is a gram negative cocobacilli spread by air born drop let
THEMATIC APPERCEPTION TEST(TAT) cognitive abilities, creativity, and critic...
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hematic appreciation test is a psychological assessment tool used to measure an individual's appreciation and understanding of specific themes or topics. This test helps to evaluate an individual's ability to connect different ideas and concepts within a given theme, as well as their overall comprehension and interpretation skills. The results of the test can provide valuable insights into an individual's cognitive abilities, creativity, and critical thinking skillsNucleic Acid-its structural and functional complexity.
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20240520 Planning a Circuit Simulator in JavaScript.pptx
Evaporation step counter work. I have done a physical experiment.
(Work in progress.)
The use of Nauplii and metanauplii artemia in aquaculture (brine shrimp).pptx
Although Artemia has been known to man for centuries, its use as a food for the culture of larval organisms apparently began only in the 1930s, when several investigators found that it made an excellent food for newly hatched fish larvae (Litvinenko et al., 2023). As aquaculture developed in the 1960s and ‘70s, the use of Artemia also became more widespread, due both to its convenience and to its nutritional value for larval organisms (Arenas-Pardo et al., 2024). The fact that Artemia dormant cysts can be stored for long periods in cans, and then used as an off-the-shelf food requiring only 24 h of incubation makes them the most convenient, least labor-intensive, live food available for aquaculture (Sorgeloos & Roubach, 2021). The nutritional value of Artemia, especially for marine organisms, is not constant, but varies both geographically and temporally. During the last decade, however, both the causes of Artemia nutritional variability and methods to improve poorquality Artemia have been identified (Loufi et al., 2024).
Brine shrimp (Artemia spp.) are used in marine aquaculture worldwide. Annually, more than 2,000 metric tons of dry cysts are used for cultivation of fish, crustacean, and shellfish larva. Brine shrimp are important to aquaculture because newly hatched brine shrimp nauplii (larvae) provide a food source for many fish fry (Mozanzadeh et al., 2021). Culture and harvesting of brine shrimp eggs represents another aspect of the aquaculture industry. Nauplii and metanauplii of Artemia, commonly known as brine shrimp, play a crucial role in aquaculture due to their nutritional value and suitability as live feed for many aquatic species, particularly in larval stages (Sorgeloos & Roubach, 2021).
Remote Sensing and Computational, Evolutionary, Supercomputing, and Intellige...
Remote Sensing and Computational, Evolutionary, Supercomputing, and Intellige...University of Maribor
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Aleš Zamuda: Remote Sensing and Computational, Evolutionary, Supercomputing, and Intelligent Systems.
11th International Conference on Electrical, Electronics and Computer Engineering (IcETRAN), Niš, 3-6 June 2024
Inter-Society Networking Panel GRSS/MTT-S/CIS Panel Session: Promoting Connection and Cooperation
https://www.etran.rs/2024/en/home-english/Recently uploaded (20)
What is greenhouse gasses and how many gasses are there to affect the Earth.
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bordetella pertussis.................................ppt
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Linkage/class 12 biology
- 1. Linkage DAMBAR SINGH KHATRI PMV BENI, MYAGDI
- 2. School : Prakash Secondary School, Beni Myagdi Unit : Genetics Time: 40 min Topic : Linkage Period: 2nd 5/20/2021 Dambar Singh Khatri 2
- 3. Teaching adds Ppt slide, online teaching method 5/20/2021 Dambar Singh Khatri 3
- 4. Behavioral objectives Students will be able to Define the concept of linkage. Differentiate incomplete and complete linkage. Explain the types of linkage. Compute the complete and incomplete through the example of drosophila and maize. 5/20/2021 Dambar Singh Khatri 4
- 5. Contents Discovery of linkage Meaning of linkage Characteristics of linkage Chromosomal theory of linkage Kinds of linkage Significance 5/20/2021 Dambar Singh Khatri 5
- 6. Discovery of Linkage The principle of linkage was discovered by English Scientists William Bateson and R.C. Punnet in 1906 in Sweet Pea (Lathyrus odoratus). However, it was put forward as a regular concept by Morgan in 1910 from his work on (Drosophila melanogaster). 5/20/2021 Dambar Singh Khatri 6
- 7. Meaning of Linkage Linkage is the phenomenon of certain genes staying together during inheritance through several generations without any change or separation due to their being present on same chromosomes. 5/20/2021 Dambar Singh Khatri 7
- 8. CHARACTERISTICS OF LINKAGE Linkage involves two or more genes which are linked in same chromosomes in a linear fashion. Linkage reduces variability. It may involve either dominant or recessive alleles(coupling phase) or some dominant and some recessive alleles(repulsion phase). It usually involves those genes which are located close to each other. The strength of linkage depends on the distance between the linked gene. Lesser the distance higher the strength of linkage. 5/20/2021 Dambar Singh Khatri 8
- 9. Chromosome theory of linkage Morgan and Castle associate genes with chromosome and formulated postulates. The genes which show Linkage are located in same chromosome. The distance between linked gene in the chromosome determine the strength of linkage. The genes lie in a linear manner in the chromosomes. 5/20/2021 Dambar Singh Khatri 9
- 10. Kinds of linkage Complete linkage Incomplete linkage 5/20/2021 Dambar Singh Khatri 10
- 11. Complete linkage The phenomenon in which the genes present in single chromosome donot separate and inherit together in the successive generations due to the absence of crossing over is called complete linkage. Hence it produce parental combinations but not non-parental combinations. It is very rare in nature but found in male drosophila. Eg. A cross between grey body normal wing(GGNN) with black body vestigial wing(ggnn). 5/20/2021 Dambar Singh Khatri 11
- 12. When grey body normal wing crossed with black body vestigial wing, the F1 offspring are grey body and normal wing. When these F1 hybrids are crossed with recessive parents having black body and vestigial wings( test cross), it produces two types offspring in equal proportion in F2 generation. Hence grey body color is inherited with normal wings and black body color is inherited with vestigial wings. It means these genes are linked genes and no non- parental combinations are formed due to the absence of crossing over. 5/20/2021 Dambar Singh Khatri 12
- 13. Complete and incomplete linkage 5/20/2021 Dambar Singh Khatri 13
- 14. Incomplete linkage The phenomenon in which linked genes present in the same chromosome have tendency to separate due to crossing over and forms both parental and non- parental combinations in the F2 generation is called incomplete linkage. for eg. When coloured full seed (CCFF) of maize is crossed with colourless shrunken seed(ccff) of maize. 5/20/2021 Dambar Singh Khatri 14
- 15. From above cross, the F1 offspring were coloured and full(CcFf). When F1 hybrid is crossed with recessive parents i.e. colourless shrunken, they produce both parental and non- parental combinations with four combinations with four phenotypes in the ratio of 1:1:1:1 i.e. 1 coloured full: 1 coloured shrunken: 1 colourless full:1 colouress shrunken. This is due to incomplete linkage. 5/20/2021 Dambar Singh Khatri 15
- 16. Example of incomplete linkage 5/20/2021 Dambar Singh Khatri 16
- 17. Significance of linkage It reduce the chances of formation of new combinations of genes in gametes. It helps keeping the parental, racial and specific traits together. It also useful for maintaining the good character of newly developed variety. Linkage plays an important role in determining the nature and scope of hybridization. 5/20/2021 Dambar Singh Khatri 17