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Meiosis

Meiosis. Production of gametes. Why Meiosis?. Meiosis is the production of our sex cells (gametes). 23 chromosomes. 23 chromosomes. How does meiosis occur?. The nucleus must divide TWICE in order to end up with a haploid (1n) sperm or egg. Two main steps : Meiosis I Meiosis II.

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Meiosis

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  1. Meiosis Production of gametes

  2. Why Meiosis? • Meiosis is the production of our sex cells (gametes). 23 chromosomes 23chromosomes

  3. How does meiosis occur? • The nucleus must divide TWICE in order to end up with a haploid (1n) sperm or egg. • Two main steps: • Meiosis I • Meiosis II

  4. Homologous chromosomes – have the same sequence of genes, size and structure (one from mom and one from dad) • Sister chromatids – when a chromosome has replicated (the two copies)

  5. The cell starts with homologous chromosomes. During Interphase I of meiosis, chromosomes are replicated. Two Main Steps: Meiosis I- homologous chromosomes separate produces haploid cells with replicated chromosomes Meiosis II- sister chromatids separate produces haploid cells with unreplicated chromosomes

  6. Chromosomes DO NOT replicate between meiosis I and meiosis II.

  7. Are the 4 daughter cells of meiosis alike or different? DIFFERENT How can we tell??? We don’t look exactly like our brothers, sisters, or parents…

  8. Genetic Variation • Independent Assortment • Random distribution of homologous chromosomes • Crossing Over • Genetic exchange of material (during prophase I) • Random Fertilization • Random joining of two gametes (each gamete is produced independently)

  9. Spermatogenesis • The process by which sperm are made 2n n n

  10. Oogenesis • The process by which egg cells (female gametes) are made • Notice that during cytokinesis following meiosis I, the cytoplasm divides unequally. The cell that gets nearly all of the cytoplasm goes on to become the egg (ovum). Polar bodies die.

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