BIO chp10

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BIO chp10
2011-03-24 22:48:04
Meiosis sexual reproduction biology

chapter 10 of the biology textbook which talks about meiosis and sexual reproduction
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  1. Diploid Cells
    Two copies of each chromosome (one from each parent)

    Human cells are diploid
  2. Meiosis
    • Making sex cells
    • (egg and sperm...often referred as "gametes")

    • Gametes have half the genetic information,
    • they are haploid (one copy of each chromosome)
  3. The Process of Meiosis
  4. Zygote
    The diploid result when a haploid sperm and haploid egg fuse together
  5. Steps of Meiosis
    • one round of chromosome duplication
    • followed by two rounds of cell division (Meiosis I and Meiosis II)
  6. Meiosis I
    • Cells start off as diploid & Chromosomes have been duplicated:
    • -Prophase I
    • -Metaphase I
    • -Anaphase I
    • -Telephase I

    Result: 2 haploid cells
  7. Tetrads
    • homologous chromosomes exhange reciprocal sections
    • Takes place in Prophase I
  8. Metaphase I
    Microtubles move homologuous chromosomes to metaphase plate (different than metaphase in mitosis!!)

  9. Anaphase I
    • Microtubles separate homologous chromosomes
    • --Sister chromatids remain together!
  10. Telophase I
    • Nuclear envelope reforms
    • spindle dissasembles
    • 2 cells result from cytokinesis
  11. Meiosis I: Overview
  12. Meiosis II
    • Another Round of division
    • -2 daugher cells made in Meiosis I divide again
    • -this time, no DNA replication in between

    This time, sister chromatids separate

    Result: 4 haploid daughter cells
  13. Meiosis II: overview
  14. So all together....
  15. How to have Genetic Diversity
    Gametes created by meiosis are genetically different from each other

    • 2 Events:
    • Crossing Over (formation of tetrads)
    • Independent Assortment
  16. Independent Assortment
    Random distribution of homologous chromosome pairs during Metaphase I

  17. Importance of genetic diversity
    • ensures offspring will be unique
    • more genomes for natural selection to choose from
    • depedent on mutation or "horizontal" gene transfer (bacteria clonal strains)
  18. Which diploid cells undergo division to form gametes?
    • Males: Spermatogonium
    • Females: Ooogonium
  19. Sperm formation in males
    Spermatogenesis starts at puberty and continues through life

    • Spermatogonium - "stem" sex cells:
    • -- can go on to make sperm
    • OR
    • --can go on to make more spermatogonia
  20. Spermatogenesis
  21. About Oogenesis
    • All or most potential gametes produced before birth
    • meiotic divisions unequal, leading to formation of polar bodies
    • puberty releases the "arrested state" of primary oocytes, leading to ovulation
    • Meiosis II does not occur until fertilization of 2nd oocyte
    • Ovulation and reproduction naturally end during menopause
  22. Oogenesis
  23. Asexual Reproduction
    reproduction that does not require sex

    NOTE: only birds and mammals are ALL strictly sexually producing types of organisms..
  24. Forms of asexual reproduction
    Parthenogenesis: embryo develops from unfertilized egg

    • Binary Fission: cell division resulting in 2 single-celled organisms
    • --Different from meosis, two new cellls, not similar cells

    • Vegetative reproduction: in plants, new individuals are made without seeds.
    • **in animals: regeneration
  25. Hermaphroditism
    • Have both male and female reproductive parts
    • Variation on sexual reproduction

    • Example:
    • Pea plants
    • Earthworms
  26. Differences between Mitosis and Meiosis
    • Mitosis:
    • diploid
    • all the same
    • all other cells

    • Meiosis:
    • haploid
    • sex cells
    • all different