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Meiosis

Meiosis. Mitosis Review animation. Asexual (vegetative) Reproduction-. one parent produces an offspring Uses only mitosis Produces genetically identical offspring (each offspring is an exact copy of the original organism) Rapid - no need to find mates

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Meiosis

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  1. Meiosis

  2. Mitosis Review animation

  3. Asexual (vegetative) Reproduction- • one parent produces an offspring • Uses onlymitosis • Produces genetically identical offspring (each offspring is an exact copy of the original organism) • Rapid- no need to find mates • No mechanism for genetic diversity- works well in a stable, unchanging environment.

  4. Sexual Reproduction- • the formation of a new individual by a combination of two haploid sex cells • Uses Meiosis- a specialized type of cell division which halves the # of chromosomes in a gamete • Female Gamete • egg (ovum) • Male Gamete • sperm • Requires Fertilization- • the union of a sperm and an egg • (N + N = 2N) • Makes a zygote- • the product of fertilization (has two sets of chromosomes) • Causes changes in the genetic information • in order to increase the diversity in the offspring.

  5. How are the Goals of MEIOSIS Different from the Goals of MITOSIS?

  6. How Meiosis Works: Animation A few more Vocabulary Words: • Germ Cells- • Cells that give rise to the gametes of organisms • They are in the process of or have the potential to undergo meiosis. • Somatic Cells- • cells that do not have the potential to form gametes • Synapsis- • The pairing of homologous chromosomes during prophase of meiosis I

  7. Tetrad- • a unit of 4 chromatids formed by a synapsed pair of homologous chromosomes, each of which has two chromatids • Crossing Over- • The process by which homologues exchange segments with each other. • Genetic Recombination- • the reshuffling of genes on a chromosome. Caused by breakage of DNA and its reunion with the DNA of a homologous chromosome.

  8. Meiosis • animation

  9. How does the process of meiosis accomplish the previously mentioned goals? • two meiotic divisions without DNA replication in between them. • Independent assortment and crossing over

  10. MEIOSIS I • Prophase 1: • Homologous sister chromatids find each other. Crossing Over can occur during the latter part of this stage. • Metaphase 1: • Homologous chromosomes align at the equatorial plate. Independent assortment happens here. • Anaphase 1: • Homologous pairs separate with sister chromatids remaining together. • Telophase 1: • Two daughter cells are formed with each daughter containing only one chromosome of the homologous pair.

  11. Meiosis II • Prophase 2: • DNA does not replicate. Sister Chromatids prep for division • Metaphase 2: • Sister chromatids align at the equatorial plate. • Anaphase 2: • Centromeres divide and sister chromatids migrate separately to each pole. • Telophase 2: • Cell division is complete. Four haploid daughter cells are obtained.

  12. Summary • One parent cell produces four daughter cells. • Daughter cells have half the number of chromosomes found in the original parent cell and with crossing over, are genetically different. • Meiosis differs from mitosis primarily because there are two cell divisions in meiosis, resulting in cells with a haploid number of chromosomes.

  13. Meiosis Square Dance • animation

  14. Independent Assortment- • The process of random segregation and assortment of chromosomes during anaphase I of meiosis resulting in the production of genetically unique gametes. • Chiasmata- • A cross-shaped structure commonly observed between homologous chromosomes during meiosis; the site of crossing-over.

  15. Random Fertilization-   • A mating system in which there is an equal opportunity for all male and female gametes to join in fertilization • This means that an egg cell representing one of eight million different genetic possibilities will be fertilized by a sperm cell representing one of eight million genetic possibilities and the resulting zygote can have any of the possible 64 trillion diploid combinations of genes.

  16. Making Gametes • Oogenesis- •   The process of ovum formation in female animals • Spermatogenesis- • The process of sperm formation in male animals

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