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Meiosis and Sexual Reproduction Overview

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Understand the processes of meiosis, sexual reproduction, and genetic diversity. Learn about chromosome inheritance, steps of meiosis, and its importance in humans and other organisms.

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Meiosis and Sexual Reproduction Overview

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  1. Agenda • Homework out • Review homework • A few cancer presentations • Meiosis • No HW

  2. 1. Replicated Chromosome 2 chromatids

  3. 2. • Mitosis creates identical cells • Growth, repair etc.

  4. 3.

  5. 4-5 • Someone draw each one on the board?

  6. Meiosis Sexual Reproduction

  7. Purpose • To allow individuals to pass on half of their chromosomes to offspring • In vertebrate animals it produces the gametes (sperm and egg cells)

  8. Homologous Chromosomes • You have 2 versions of each chromosome • They contain slightly different versions of the same genes, called alleles • You inherit one from each parent

  9. Meiosis • Produces cells that contain only 1 copy of each homologous chromosome • Also pass on one of the sex chromosomes • So each gamete contains 22 autosomal chromosomes and an X or Y chromosome

  10. Steps of Meiosis • Very similar to mitosis, except they happen twice

  11. Meiosis I • Instead of the replicated chromosomes being separated – the homologous chromosomes get pulled apart

  12. Meiosis II • Similar to mitosis, except the cell begins with only half the chromosomes

  13. Why Sexual Reproduction? • Because diversity is good! • Increases chances that our species will survive • Meiosis produces an incredible amount of diversity

  14. How? • You can get either 1 of your mother’s pair of chromosomes for all 23 • So you can get 1A2A3A…23A, 1B2A3A..23A, 1A2B3A…23A- basically a whole lot of combinations • You get genes from your mother and your father- new combinations can be beneficial

  15. In Humans • The ovaries/testes contain cells called germ cells which undergo meiosis • Produce sperm and egg (23 chromosomes) • Sperm and egg fuse in fertilization forming a zygote

  16. Bacteria • Simply divide asexually • No mixing of genes- offspring are identical

  17. Single Celled Eukaryotes • Often divide simply by mitosis • All offspring are identical

  18. Haplodiploidy • In bees, wasps and ants unfertilized eggs develop into males • Only half one set of chromosomes • Fertilized eggs develop into females • Have 2 sets of chromosomes

  19. Hermaphroditic Eukaryotes • No male/female division – individuals can make both sperm and egg • Most plants • Many snails and other solitary creatures • Still require other individuals to reproduce with (usually) http://www.youtube.com/watch?v=FhVi4Z6CjZk

  20. Sequential Hermaphroditism • In a group of clownfish only one individual is the female and one is the male • When the female dies, the male grows and turns into the female • Another fish can then assume the role of the male If Nemo is lucky he might one day become a man… then a woman.

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