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Meiosis

Meiosis. Types of Human Cells. Sex Cells Gametes (germ cells) Eggs and Sperm Somatic Cells All other cells. Types of Chromosomes. Autosomes – same number in males and females Sex Chromosomes – X or Y Human females: XX Human males: XY

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Meiosis

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  1. Meiosis

  2. Types of Human Cells • Sex Cells • Gametes (germ cells) • Eggs and Sperm • Somatic Cells • All other cells

  3. Types of Chromosomes • Autosomes – same number in males and females • Sex Chromosomes – X or Y • Human females: XX • Human males: XY • Testosterone and other hormones from the Y make a male

  4. Humans • 46 chromosomes • (23 pairs)

  5. Ploidy • Describes how many sets of different chromosomes a cell has. • n = number of chromosomes in 1 set (haploid number) • Haploid Cells: 1n • Diploid Cells: 2n • In humans, n = 23 (the number of different chromosomes we have) 32/16 62

  6. Figure 13.5 Haploid gametes (n 23) Key Haploid (n) Egg (n) Diploid (2n) Sperm (n) MEIOSIS FERTILIZATION Ovary Testis Diploidzygote(2n 46) Mitosis anddevelopment Multicellular diploidadults (2n 46)

  7. Figure 13.6 Key Haploid (n) Haploid unicellular ormulticellular organism Haploid multi-cellular organism(gametophyte) Diploid (2n) Gametes n n Mitosis Mitosis Mitosis Mitosis n n n n n n n n Spores n MEIOSIS FERTILIZATION n Gametes n Gametes MEIOSIS FERTILIZATION FERTILIZATION MEIOSIS Zygote 2n 2n 2n 2n Diploidmulticellularorganism(sporophyte) Zygote 2n Diploidmulticellularorganism Mitosis Mitosis Zygote (a) Animals (b) Plants and some algae (c) Most fungi and some protists Plants and some algae exhibit an alternation of generations.

  8. Crossing Over • In crossing over, nonsister chromatids exchange DNA segments. • Each pair of chromosomes forms a tetrad, a group of four chromatids. • Each tetrad usually has one or more chiasmata, X-shaped regions where crossing over occurred.

  9. Figure 13.11-1 Prophase Iof meiosis Nonsister chromatidsheld togetherduring synapsis Pair of homologs

  10. Figure 13.11-2 Prophase Iof meiosis Nonsister chromatidsheld togetherduring synapsis Pair of homologs Chiasma Centromere TEM

  11. Figure 13.11-3 Prophase Iof meiosis Nonsister chromatidsheld togetherduring synapsis Pair of homologs Chiasma Centromere TEM Anaphase I

  12. Figure 13.11-4 Prophase Iof meiosis Nonsister chromatidsheld togetherduring synapsis Pair of homologs Chiasma Centromere TEM Anaphase I Anaphase II

  13. Figure 13.11-5 Prophase Iof meiosis Nonsister chromatidsheld togetherduring synapsis Pair of homologs Chiasma Centromere TEM Anaphase I Anaphase II Daughtercells Recombinant chromosomes

  14. Down Syndrome

  15. Klinefelter’s Syndrome

  16. Cause: Nondisjunction

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