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Meiosis I and II Stages

Meiosis I and II Stages. December 6, 2011. Meiosis I. PROPHASE I:. Tetrad Formation Homologous pairs connect to each other. Synapsis : homologous chromosomes come together & line up side by side Crossing-over : Exchange of genetic info between non-sister chromatids.

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Meiosis I and II Stages

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  1. Meiosis I and II Stages December 6, 2011

  2. Meiosis I • PROPHASE I: Tetrad Formation Homologous pairs connect to each other Synapsis: homologous chromosomes come together & line up side by side Crossing-over: Exchange of genetic info between non-sister chromatids 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 Letters denote genes, Case denotes alleles (dominant vs recessive versions of the trait) E E e e 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 Letters denote genes, Case denotes alleles (dominant vs. recessive versions of the trait) E E e e F F f f • Creates chromosomes with new combinations of alleles for genes A to F.

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

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

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

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

  10. Meiosis II • PROPHASE II: Centrioles start to move to the poles Spindle starts to form Nuclear envelope and nucleousdisappear

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

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

  13. 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

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

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