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Meiosis

Meiosis. Unit 4 – Lecture 2. Discuss. Review the stages of Mitosis [cell cycle] with your partner. Mitosis – cell division in somatic [body] cells [I]PMAT [ interphase ] prophase metaphase anaphase telophase. Meiosis. Meiosis – cell division to create gametes

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Meiosis

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  1. Meiosis Unit 4 – Lecture 2

  2. Discuss • Review the stages of Mitosis [cell cycle] with your partner. • Mitosis – cell division in somatic [body] cells • [I]PMAT • [interphase] • prophase • metaphase • anaphase • telophase

  3. Meiosis • Meiosis – cell division to create gametes • sex cells / reproductive cells / egg&sperm • Meiosis I – • IPMAT • Meiosis II – • PMAT

  4. Meiosis I • Meiosis I – similar to mitosis [diff in red] • [interphase…] • Prophase I • chromosomes condense • nuclear envelope disappears • homologous chromosomes pair • instead of chromatids • crossing over occurs

  5. Crossing Over • Crossing over – exchange of genetic information between homologous chromosomes • contributes to genetic diversity of resulting gametes • homologous chromosome pair = tetrad • tetra = four • not required: chiasma(ta) – place at which crossing over occurs

  6. Meiosis I – cont’d • [Meiosis I] • Metaphase I • spindle fibers move tetrads to cell equator[similar to metaphase plate / equatorial plate in mitosis]

  7. Meiosis I – cont’d • [Meiosis I] • Anaphase I • homologous chromosomes are each pulled by spindle fibers to cell poles

  8. Meiosis I – cont’d • [Meiosis I] • Telophase I • homologous chromosomes each arrive at cell poles • nuclear envelopes reform • spindle fibers break down • cytoplasm divides [cytokinesis]

  9. Meiosis I – cont’d • Meiosis I: End Result – • 2 diploid cells with: • same amount of information • different combination of information

  10. Meiosis II • Meiosis II – • process is just like mitosis • NO SECOND INTERPHASE. [PMAT]

  11. Discuss • What processes happen during interphase? • If there is no interphase, what processes are NOT going to happen in between the first stages of meiosis and the second meiosis?

  12. Meiosis II – cont’d • [Meiosis II] • Prophase II • spindle fibers form • nuclear envelopes dissolve

  13. Meiosis II – cont’d • [Meiosis II] • Metaphase II – • chromosomes line up at equator

  14. Meiosis II – cont’d • [Meiosis II] • Anaphase II • chromosomes pulled apart at centromeres; [form chromatids] • chromosomes [chromatids] pull toward poles

  15. Meiosis II – cont’d • [Meiosis II] • Telophase II – • nuclear envelopes reform • spindle fibers break down • cytokinesis

  16. Meiosis II – cont’d • Meiosis II: End Result – • 4 haploid cells with: • half of info as original cell • different combination of information

  17. Meiosis – cont’d • Cells produced from meiosis are genetically different • due to: • crossing over [in prophase I] • independent assortment [in metaphase I] • random distribution of homologues in metaphase I

  18. Meiosis – cont’d • More than 8 million [223] combinations of genes in humans PER PARENT [w/ only IA] • total…with 2 parents combining genes…= >70 trillion combinations [223 * 223]

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