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Meiosis

Meiosis. Review: Mitosis. Mitosis = cell division in body cells (one cell makes two cells, chromosome number is the same) Start with 46 chromosomes, end with 2 cells, each with 46 chromosomes. I P M A T. Meiosis – The key to our differences:. How do organisms reproduce?.

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Meiosis

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  1. Meiosis

  2. Review: Mitosis • Mitosis = cell division in body cells (one cell makes two cells, chromosome number is the same) • Start with 46 chromosomes, end with 2 cells, each with 46 chromosomes. • I P M A T

  3. Meiosis – The key to our differences: How do organisms reproduce? Why do you share some but not all characters of each parent? How does heredity information pass from one generation to the next? At one level, the answers lie in meiosis.

  4. Animal Reproduction • Each organism has 2 sets of genetic information (2 sets of chromosomes) • One set from dad • One set from mom • One set comes from the EGG and the other set comes from the SPERM.

  5. Chromosomes • Each of us have TWO of each chromosome. • 1 from mom and 1 from dad. • Humans have 46 chromosomes.

  6. The PROBLEM? • How does each parent donate only 23 chromosomes each to their baby when their cells each have 46 chromosomes? • MEIOSIS is the answer!! • Not all cells reproduce by mitosis

  7. Why do we need meiosis? • Meiosis is necessary to split in half the number of chromosomes going into the sex cells Why split the chromosomes in sex cells? • At fertilization the male and female sex cells will provide ½ of the chromosomes each – so the offspring has genes from both parents

  8. Meiosis • Cell division of Reproductive cells (sperm and egg ONLY!) • One cell becomes four cells, chromosomes # is half! • This is because the cell divides TWO times!! • I P M A T P M A T

  9. Meiosis Parent cell – chromosome pair 46 chromosomes Chromosomes copied 92 chromosomes 1st division - pairs split 46chromosomes 46chromosomes 2nd division – produces 4 sex cells with ½ the original no. of chromosomes 23 23 23 23

  10. Meiosis – mouse testes Parent cell 1st division 2nd division 4 sex cells

  11. Interphase • Cell GROWS • DNA copies • Chromosome copy = sister chromatids

  12. MEIOSIS I

  13. Figure 13.7 The stages of meiotic cell division: Meiosis I

  14. MEIOSIS II

  15. Figure 13.7 The stages of meiotic cell division: Meiosis II

  16. Meiosis Vs. Mitosis • Meiosis (My-O-SEX) • Sex Cells • Start with 1 cell and end with 4 cells • Ending cells have ½ the number of chromosomes • Divides 2 times (PMATPMAT) • Mitosis (My-TOE-sis) • Body Cells • Start with 1 cell and end with 2 cells • Ending cells have same number of chromosomes • Divides 1 time (PMAT)

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