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Pre IB Genetics (Intro to Chromosomes)
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Pre IB Genetics (Intro to Chromosomes) Pre IB Genetics (Intro to Chromosomes) Presentation Transcript

    • The Cellular Basis of Reproduction and Inheritance
    • Introduction
    • Stages of an Organism’s Life Cycle :
    • Development : All changes that occur from a fertilized egg or an initial cell to an adult organism .
    • Reproduction : Production of offspring that carry genetic information in the form of DNA, from their parents.
    • Two types of reproduction:
      • 1. Sexual Reproduction
      • 2. Asexual Reproduction
    • Types of reproduction
      • 1. Sexual Reproduction :
      • Male and female gametes or sex cells (sperm and egg cell) join together to create a fertilized egg or zygote .
      • Offspring are genetically different from each parents and their siblings. The differences in individuals is due to various found in the DNA that is organized on genes contained on chromosomes .
    • There are two types of chromosomes
    • A. Autosomes: Found in both males and females.
    • In humans there are 22 pairs of autosomes .
    • B. Sex Chromosomes : Determine an individual’s gender. In Humans and other mammals females are XX and males are XY.
    • *The Y chromosome has a small number of genes.
  • Two types of chromosomes
  • 2. Asexual Reproduction :
      • Production of offspring by a single parent :
      • Example:
        • Splitting : Binary fission (equal division) in bacteria.
        • Budding : (unequal division) Yeasts, plants
    Binary fission Budding
  • 2. Asexual Reproduction : Continued
      • Advantages :
        • Can reproduce without a partner of opposite sex.
        • Don’t spend time, energy, and resources to find a suitable mate.
      • Disadvantage :
        • No genetic diversity of offspring.
          • Population less likely to survive changing environment.
    • Two types of cells
    • Diploid Cells: Cells whose nuclei contain two homologous sets of chromosomes (2n).
      • Somatic cells are diploid (almost all cells in our body).
      • In humans the diploid number 2(23) is 46.
    • Haploid Cells: Cells whose nuclei contain a single set of chromosomes (n).
      • Gametes are haploid (egg and sperm cells).
      • In humans the haploid number (n) is 23.
    • Fertilization: Haploid egg fuses with a haploid sperm to form a diploid zygote (fertilized egg).
  • Haploid Gametes are produced from Diploid Parents Fertilization Produces Diploid Offspring from Haploid Gametes
  • Cell Cycle of Eukaryotic Cells
    • Sequence of events from the time a cell is formed, until the cell divides.
    • Before cell division, the cell must:
          • Copy the DNA
          • double the amount of cytoplasm and organelle
    • Cell cycle is divided into two main phases:
      • Interphase : Stage between cell divisions
      • Mitotic Phase : Stage when cell is dividing
  • Functions of Mitosis in Eukaryotes:
      • 1. Growth: All somatic cells that originate after a new individual is created are made by mitosis.
  • Functions of Mitosis in Eukaryotes:
      • 2. Cell replacement: Cells that are damaged or destroyed due to disease or injury are replaced through mitosis.
  • Functions of Mitosis in Eukaryotes:
      • 3. Asexual Reproduction: Mitosis is used by organisms that reproduce asexually to make offspring.
  • Eukaryotic Cell Cycle: Interphase + Mitotic Phase
    • The Life Cycle of a Eukaryotic Cell :
    • Interphase : Time between cell divisions or 90% of a cells life .
    • Interphase can be divided into three stages:
      • 1. G 1 phase : Just after cell division. Cell grows in size, increase number of organelles, and makes proteins needed for DNA synthesis.
      • 2. S phase : DNA replication. Single chromosomes are duplicated so they contain two sister chromatids .
      • 3. G 2 phase : Protein synthesis increases in preparation for cell division.
  • Duplication of Chromosomes During S stage of Interphase Single chromosome Two identical sister chromatids joined by a centromere DNA replication during S stage of Interphase
    • The Life Cycle of a Eukaryotic Cell :
      • Mitosis : The process of eukaryotic cell division.
      • Most cells spend less than 10% of time in mitosis.
      • Mitosis is divided into four stages:
      • 1. Prophase
      • 2. Metaphase
      • 3. Anaphase
      • 4. Telophase
      • Cytokinesis: Cytokinesis usually occurs after mitosis, which is a division of cytoplasm.
    • Mitosis: The Stages of Cell Division
      • 1. Prophase
            • Chromatin condenses into chromosomes ,
            • which appear as two sister chromatids joined by a centromere .
            • Nuclear envelope breaks apart.
            • In animal cells, mitotic spindle begins to form.
    • Mitosis: The Stages of Cell Division
      • 2. Metaphase
        • Chromosomes line up along equatorial plane of cell
        • Chromosomes are completely condensed and easy to visualize
    • Mitosis: The Stages of Cell Division
      • 3.Anaphase
        • Sister chromatids begin to separate.
        • The separate chromosomes are pulled toward opposite poles.
    • Mitosis: The Stages of Cell Division
      • 4. Telophase
        • Nuclear envelope forms around each set of chromosomes.
        • Chromosomes uncoil, becoming chromatin threads.
        • Spindle microtubules disappear.
        • Cytokinesis usually occurs at the end of this stage
    • Cytokinesis
          • In animal cells: Division is accomplished by a cleavage furrow .
          • In plant cells: Division is accomplished by the formation of a cell plate between the daughter cells.
  • Cancer is a Disease of the Cell Cycle
    • Cancer kills 1 in 5 people in the United States.
    • Cancer cells divide excessively and invade other body tissues.
    • Tumor: Abnormal mass of cells that originates from uncontrolled mitosis of a single cell.
      • Benign tumor: Cancer cells remain in original site. Can easily be removed or treated
      • Malignant tumor: Cancer cells have ability to “detach” from tumor and spread to other organs or tissues
      • Metastasis: Spread of cancer cells form site of origin to another organ or tissue.
        • Tumor cells travel through blood vessels or lymph nodes.
  • Metastasis: Cancer Cells Spread Throughout Body
  • Types of Asexual Reproduction
    • Binary Fission
    • Budding
    • Spore Formation
    • Regeneration
    • Vegetative Propagation
  • 1. Binary Fission
    • Parent divides into two equal parts.
    • The 2 daughter cells are equal in size and grow to normal size .
    • Example : ameba and paramecium
  • Binary Fission
  • 2. Budding
    • The parent cell divides into 2 unequal parts.
    • Yeast (unicellular)
    • 2 daughter cells are produced.
    • 1 is larger than the other.
    • Hydra (multicellular)
    • The daughter is a multicellular outgrowth of the parent.
    • The small hydra bud eventually separates from the parent.
  • 3. Spore formation
    • A form of reproduction in which the organism breaks up into a number of pieces, or spores, each of which eventually develops into an organism like the parent form
  • 4. Regeneration
    • The ability of an animal to regrow lost body parts.
    • Simple organisms :
    • hydra, planaria, earthworm, and lobster
  • 5. Vegetative Propagation
    • Two types Natural and Artificial Vegetative Propagation.
    • The growing of new plants from parts of other plants.
    • Types of vegetative propagation:
    • Bulb
    • Tuber
    • Runner
    • Cutting
    • Grafting
  • I. Bulb
    • Natural Vegative Propagation
    • A bulb is an underground vertical shoot that has modified leaves (or thickened leaf bases) that are used as food storage organs by a dormant plant.
  • II. Tuber
    • Natural Vegative Propagation
    • An enlarged portion of an underground stem that contains food.
    • Example : potato
  • III. Runner
    • A fast growing stem that grows on the surface of the soil.
    • The plant runner can develop new plants off of the node
    • tip. Plant runners often have stems that grow above the
    • soil and takes root, and then become a new plant.
  • IV. Plant Cutting
    • a technique in which a piece of the plant containing at least one stem cell is placed in a suitable medium such as moist soil. The cutting produces new roots, stems, or both, and thus becomes a new plant independent of the parent
  • V. Grafting
    • Tissues of one plant are encouraged to fuse with those of another. It is most commonly used for the propagation of trees and shrubs grown commercially.
    • In most cases, one plant is selected for its roots, and this is called the stock or rootstock. The other plant is selected for its stems, leaves, flowers, or fruits and is called the scion. The scion contains the desired genes to be duplicated in future production by the stock/scion plant
  • Sexual Reproducton: Meiosis
    • The Creation of Sex Cells
    • Types of reproduction:
      • 1. Sexual Reproduction:
      • Male and female gametes or sex cells (sperm and egg cell) join together to create a fertilized egg or zygote .
      • Offspring are genetically different from each parents and their siblings.
      • Advantages :
          • Ensures genetic diversity of offspring .
        • Disadvantages:
        • Cannot reproduce without a partner of opposite sex.
        • Parents only pass on 1/2 (50%) of their genetic information to each offspring.
    • Chromosomes are matched in
    • homologous pairs
      • Normal humans have 46 chromosomes in 23 pairs.
      • One chromosome of each pair comes from an individual’s mother , the other comes from the father .
      • Homologous chromosomes carry genes that control the same characteristics .
      • Examples: Eye color, blood type,
      • flower color, or height
  • Homologous Pair of Chromosomes: One Comes From Each Parent
  • Homologous Chromosomes: Code for the Same Genetic Traits, but Have Different Alleles
    • There are two types of chromosomes :
    • 1. Autosomes : Found in both males and females.
    • Humans there are 22 pairs of autosomes .
    • 2. Sex Chromosomes: Determine an individual’s gender. In Humans and other mammals females are XX and males are XY.The X chromosome is much larger than the Y chromosome and contains many genes.
      • The Y chromosome has a small number of genes.
  • Chromosomes of Normal Human Male: 44 (22 Pairs) Autosomes + XY
    • Normal Genetic Complement of Humans:
    • Females: 44 autosomes (22 pairs) + XX
    • Males: 44 autosomes (22 pairs) + XY
    • Note : In most cases, having additional or missing chromosomes is usually fatal or causes serious defects.
    • Down’s syndrome : Trisomy 21. Individual’s with an extra chromosome 21. Most common chromosomal defect (1 in 700 births in U.S.).
    • Gametes have a single set of chromosomes
    • Humans have two sets of chromosomes, one inherited from
    • each parent.
    • Haploid Cells: Cells whose nuclei contain a single set of chromosomes (n).
      • Gametes are haploid (egg and sperm cells).
      • In humans the haploid number (n) is 23.
    • Fertilization: Haploid egg fuses with a haploid sperm to form a diploid zygote (fertilized egg).
  • Meiosis Produces Haploid Gametes From Diploid Parents Fertilization Produces Diploid Offspring from Haploid Gametes
    • Meiosis: Generates haploid gametes
    • Reduces the number of chromosomes by half.
    • Also produces genetic variability , each gamete is different, ensuring that two offspring from the same parents are never identical.
    • Two divisions: Meiosis I and meiosis II. Chromosomes are duplicated in interphase prior to Meiosis I.
  • Interphase: Chromosomes replicate Meiosis I: Reductive division. Homologous chromosomes separate Meiosis II: Sister chromatids separate STAGES OF MEIOSIS
    • Meiosis I: Separation of Homologous Chromosomes
      • 1. Prophase I:
        • Chromatin condenses into chromosomes.
        • Nuclear membrane disappear.
        • Centrosomes move to opposite poles of cell and microtubules attach to chromatids.
        • Synapsis: Homologous chromosomes pair up and form a tetrad of 4 sister chromatids.
  • Prophase I: Crossing Over Between Homologous Chromosomes Crossing over combined with Fertilization: A couple can produce over 64 trillion (8.3 million x 8.3 million) different combinations in a zygotes during fertilization.
    • Meiosis I: Separation of Homologous Chromosomes
      • 2. Metaphase I:
        • Chromosome tetrads (homologous chromosomes) line up in the middle of the cell.
        • Each homologous chromosome faces opposite poles of the cell.
    • Stages of Meiosis: Meiosis I
      • 3. Anaphase I:
        • Chromosome tetrads split up and move towards opposite poles.
          • Random assortment : increases genetic diversity of offspring. Possible combinations: 2 n .One human cell can generate 2 23 or over 8.3 million different gametes by random assortment alone.
    • Meiosis I : Separation of Homologous Chromosomes
      • 4. Telophase I and Cytokinesis:
        • Chromosomes reach opposite poles of the cell.
        • Nucleoli reorganize, chromosomes uncoil, and cytokinesis occurs.
        • New cells are haploid.
  • Random Assortment of Homologous Chromosomes During Meiosis I Generates Many Possible Gametes
    • Meiosis II : Separation of Sister Chromatids
      • During interphase that follows meiosis I, no DNA replication occurs.
      • Interphase may be very brief or absent.
      • Meiosis II is very similar to mitosis .
      • 1. Prophase II:
        • Very brief, chromosomes reform.
        • No crossing over or synapsis.
        • Spindle forms and starts to move chromosomes towards center of the cell.
    • Meiosis II : Separation of Sister Chromatids
      • 2. Metaphase II:
        • Very brief, individual chromosomes line up in the middle of the cell.
      • 3. Anaphase II:
        • Chromatids separate and move towards opposite ends of the cell.
    • Meiosis II : Separation of Sister Chromatids
      • 4. Telophase II:
        • Nuclei form at opposite ends of the cell.
        • Cytokinesis occurs.
        • Product of meiosis :
        • Four (4) haploid gametes, each genetically different from the other.
  • Meiosis Produces Four Genetically Different Gametes
    • Meiosis in Males and Females
    • Spermatogenesis:
    • Four sperm cells are made.
    • Starts in puberty and occurs continuously.
    • Males produce millions of sperm cells a month.
    • Oogenesis :
    • Only one large egg is produced. The other three cells are small polar bodies.
    • Oogenesis starts before birth in females, stops at Prophase I, and resumes during puberty.
    • Meiosis is completed only after fertilization.
    • Females make one mature egg/month .
    • Mitosis versus Meiosis (Review)
    • Mitosis Meiosis
    • One cell division Two successive cell divisions
    • Produces two (2) cells Produces four (4) cells
    • Produces diploid cells Produces haploid gametes
    • Daughter cells are genetically Cells are genetically different from
    • identical to mother cell mother cell and each other
    • No crossing over Crossing over*
    • Functions: Growth, Functions: Sexual reproduction
    • cell replacement, and
    • asexual reproduction
    • * Crossing over : Exchange of DNA between homologous chromosomes.
  • Crossing Over in Meiosis Increases Genetic Diversity
      • Nondisjunction : Chromosomes fail to separate this increases with age .
          • Gametes (and zygotes) will have an extra chromosome, others will be missing a chromosome.
    Accidents During Meiosis Can Cause Chromosomal Abnormalities
  • Trisomy
        • Trisomy : Individuals with one extra chromosome, three instead of pair. Have 47 chromosomes in cells.
  • Down’s syndrome
        • Monosomy : Missing a chromosome, one instead of pair. Have 45 chromosomes in cells.
  • Monosomy
  • Turner’s Syndrome
    • Accidents During Meiosis Can Result in a Trisomy or Monosomy
      • Most abnormalities in numbers of autosomes are very serious or fatal.
        • Down’s syndrome : Caused by a trisomy of chromosome number 21 (1 in 700 births). Mental retardation, mongoloid features, and heart defects.
      • Most abnormalities of sex chromosomes do not affect survival.
        • Klinefelter Syndrome : Males with an extra sex chromosome (XXY) (1 in 1000 male births).
        • Turner Syndrome : Females missing one sex chromosome (XO) (1 in 2500 female births).