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MEIOSIS

MEIOSIS. The Source of Genetic Variation in Eukaryotes. What’s good about asexual reproduction by mitosis?. Rapid rate of reproduction is possible Offspring are clones of their parents Successful organisms continue to be successful in their environment

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MEIOSIS

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  1. MEIOSIS The Source of Genetic Variation in Eukaryotes

  2. What’s good about asexual reproduction by mitosis? • Rapid rate of reproduction is possible • Offspring are clones of their parents • Successful organisms continue to be successful in their environment • Doesn’t require specialized cells or organs • Examples: Cuttings, budding yeast, binary fission in bacteria, parthenogenesis, runners

  3. What’s wrong with asexual reproduction? • All members of a population are genetically identical • If one member of the population is susceptible to a disease, they are all susceptible • No ability to adapt to changes in the environment • Evolution is not possible except in the case of bacteria or viruses

  4. Corn Blight of 1970 • “As it was, the Southern Corn Leaf Blight devastated 15 percent of America's 1970 corn crop, reducing the average national corn yield from 83.9 to 71.7 bushels per acre, costing farmers about $1 billion in losses. Some southern states lost more than 50 percent of their corn crop. In all, more than 1.02 billion bushels of corn were lost in 1970. But the crisis wasn't over.” http://www.unsafescience.com/cms-sclb.html

  5. Terms to Review • Genes = Hereditary units • Karyotype • Homologous chromosomes • Sex chromosomes • Autosomes • Haploid vs. Diploid: n vs. 2n • Zygote • Syngamy

  6. Meiosis produces 4 haploid gametes from a diploid mother cell 2n Chromosomes segregate by independent assortment at Metaphase 1 Single chromosomes consisting of two sister chromatids are present after the first meiotic division n Four haploid gametes result after the 2nd meiotic division. Each cell contains one member of each original pair of chromosomes n

  7. Synapsis occurs, tightly “locking” the chromosomes together 4 chromosomes become visible, connected by chiasmata: crossing over of non-sister chromatids Homologous chromosomes attach to the same spindle fiber Homologous chromosomes separate (Segregate) independently Sister chromatids separate

  8. Spermatogenesis

  9. Oogenesis

  10. COMPARE

  11. Three Sources of Genetic Variation • Independent assortment of homologous chromosomes during meiosis 1 and of non-identical sister chromatids during meiosis 2 • Crossing over between homologous chromosomes during prophase of meiosis 1 • Random fertilization of an ovum by a sperm

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