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Meiosis

Meiosis. Making Sex Cells. Why Did Sex Evolve in the First Place?. The simplest method of reproduction is asexual reproduction . Asexual reproduction results in offspring that are clones of the parent organism.

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Meiosis

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  1. Meiosis Making Sex Cells

  2. Why Did Sex Evolve in the First Place? • The simplest method of reproduction is asexual reproduction. Asexual reproduction results in offspring that are clones of the parent organism. • Asexual reproduction is favored when the environment is relatively stable, because if the parent is well-adapted to the environment, their offspring will be well-adapted too.

  3. Aww, how cute. It looks exactly like me…

  4. Why Did Sex Evolve in the First Place? • So why reproduce sexually? Sexual reproduction gives organisms the opportunity to combine their genetic information with that of another organism. • As a result, their offspring typically have a greater variety of traits than those produced by asexual reproduction.

  5. Why Did Sex Evolve in the First Place? Asexual reproduction: Parent: Large leaves ↓ Offspring: All large leaves

  6. Why Did Sex Evolve in the First Place? Sexual reproduction: Parents: Large leaves + Small leaves ↓ Offspring: Some large, some medium, some small

  7. How Are Sex Cells Made? • Sex cells, also known as gametes, are made through the process of meiosis. • Gametes are sperm and eggs. • In humans, gametes are produced by the reproductive system.

  8. What Is Meiosis? • Meiosis is a 2-stage process by which the chromosome number in a cell is reduced by ½ • A somatic cell (a body cell) is called a diploid cell because it contains a full set of chromosomes. • A gamete (a sex cell) is called a haploid cell because it contains a half set of chromosomes.

  9. 1. A somatic cell from a ring tailed lemur has 56 chromosomes. How many chromosomes will be in one of these lemur’s gametes? ______ 2. Is this gamete haploid or diploid? _______

  10. 3. What would happen if gametes did not go through meiosis? ____________________________________________________________________

  11. How Does Meiosis Increase Genetic Diversity? • Meiosis increases the diversity of the traits in the offspring in 2 ways: • Crossing over – During prophase I of meiosis, homologous chromosomes form a tetrad and exchange DNA

  12. Crossing Over – Draw This New combination of DNA

  13. How Does Meiosis Increase Genetic Diversity? • Independent assortment – homologous chromosomes line up independently – they can line up in any order • So, the gametes are NOT ALL THE SAME

  14. Independent Assortment

  15. So How Do The Gametes Get Together? • When gametes combine, it is called fertilization • The resulting cell is called a zygote. Over time, the zygote will grow into an embryo.

  16. So How Do The Gametes Get Together? • External fertilization – many gametes are released into water by both sexes • Internal fertilization – the male often has a copulatory organ (penis) for transferring sperm to the egg

  17. External Fertilization

  18. Internal Fertilization

  19. How Does This Compare to Mitosis?

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