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Meiosis Part 2

Meiosis Part 2

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Meiosis Part 2

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  1. Meiosis Part 2 SBI 3U November 4th, 2012

  2. Recall • What is the function of meiosis? • How many cell divisions are there in the process of meiosis?

  3. Random Assortment of Chromosomes • Random assortment of chromosomes during Anaphase I • 1 of the ways by which meiosis creates genetic variability • 2n=46  how many variations can we have?

  4. Crossing Over • Genetic recombination • During prophase of Meiosis I • Breakage and reunion of chromatids • Large genetic diversity

  5. Sperm & Egg Cells • Spermatids: in male animals. 4 functional cells  later become sperm cells -Have a head (containing nucleus) -Have a tail (flagellum) -Middle piece (containing mitochondria)

  6. Spermatogenesis

  7. Sperm & Egg Cells • In meiosis I  division of the cytoplasm is unequal = one large cell (a secondary oocyte) and one small cell (the first polar body) • Polar body contains only the nucleus • Oogenesis

  8. Sperm & Egg Cells • Meiosis II  secondary oocyte divides unequally again = one large ovum/egg and a small polar body • End of meiosis for females: 1 egg

  9. Mistakes in Meiosis • Mistakes may be in separation of the chromosomes during division or an incorrect exchange of genetic information • Mistake in separation of chromosomes during division: Can result in an abnormal # of chromosomes in an egg or sperm cell

  10. Mistakes in Meiosis • Resulting zygote will have too few or too many chromosomes: aneuploidy • Down syndrome • Mistake in exchange of information during crossing over: correct # of chromosomes but altered genetic information

  11. Mistakes in Meiosis • Altered chromosomes may contain duplications or deletions

  12. Abnormal Chromosome Number • Nondisjunction occurs when the homologous chromosomes do not split properly during meiosis I or the sister chromatids do not separate during meiosis II • What will happen to the resulting gametes?

  13. Abnormal Chromosome Number • Monosomy: when a child only has 1 copy of a chromosome • Polysomy: when a child has 3 copies of a particular chromosome • Polyploidy: 3 sets of chromosomes! Very rare.

  14. Abnormal Chromosomal Structure • Occurs during crossing over • Deletions and duplications • If a segment reattaches to a complete homolog, there will be a duplication • If a segment reattaches to the correct homolog  inversion

  15. Abnormal Chromosomal Structure • Translocation: segment attaches to a non-homologous chromosome