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Meiosis I and II Stages

Meiosis I and II Stages. December 9, 2011. Meiosis I. PROPHASE I :. Synapsis : homologous chromosomes come together & line up side by side Crossing-over : Exchange of genetic info between non-sister chromatids occurs at the chiasmata. Centrioles start to move to the poles.

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Meiosis I and II Stages

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  1. Meiosis I and II Stages December 9, 2011

  2. Meiosis I • PROPHASE I: Synapsis: homologous chromosomes come together & line up side by side Crossing-over: Exchange of genetic info between non-sister chromatids occurs at the chiasmata Centrioles start to move to the poles Spindle starts to form Nuclear envelope and nucleousdisappear

  3. A A a a B B b b C C c c D D d d E E e e F F f f Recombination (crossing over) • Occurs in prophase of meiosis I • Generates diversity • Creates chromosomes with new combinations of alleles for genes A to F.

  4. Recombination (crossing over) A a a A B • Occurs in prophase of meiosis I • Generates diversity b b B c C C c D D d d E E e e Letters denote genes Case denotes alleles F F f f • Creates chromosomes with new combinations of alleles for genes A to F.

  5. Recombination (crossing over) a A a A B b B • Occurs in prophase of meiosis I • Generates diversity b c c C C D D d d E E e e Letters denote genes Case denotes alleles F F f f • Creates chromosomes with new combinations of alleles for genes A to F.

  6. Independent Assortment

  7. Independent Assortment: Homologous pairs independently align along metaphase plate • METAPHASE I: Spindle fibers attach to centromere of each homologous pair

  8. ANAPHASE I: Homologous pairs separate and are drawn to opposite poles by spindle fibers Centromeres remain intact

  9. Nuclear envelope and nucleousreappear Daughter cells have one chromosome from each homologous pair. • TELOPHASE I: Cleavage Furrow Spindle fibers disappear

  10. INTERKINESIS: Period of time between Meiosis I and Meiosis II No replication of DNA occurs

  11. Meiosis II-DOESN’T THIS LOOK FAMILIAR?? YES… IT’S JUST LIKE MITOSIS!!! • PROPHASE II: REMEMBER THERE ARE ACTUALLY 2 CELLS GOING THROUGH MEISOSIS II AND THOSE 2 CELLS DIVIDE INTO 4 CELLS AT THE END OF THIS PROCESS Centrioles start to move to the poles Spindle starts to form Nuclear envelope and nucleousdisappear

  12. Replicated chromosomes align at the metaphase plate • METAPHASE II: Spindle fibers attach to centromere of each sister chromatid

  13. ANAPHASE II: Sister chromatids separate and are drawn to opposite poles by spindle fibers Centromeres are broken

  14. Nuclear envelope and nucleousreappear Daughter cells have one unduplicated chromosome from each sister chromatid. Have haploid number (“n”) of chromosomes • TELOPHASE II: Cleavage Furrow Spindle fibers disappear

  15. CYTOKINESIS: Division of cytoplasm Separation of 4 haploid daughter cells

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