Download
girls exploring physics n.
Skip this Video
Loading SlideShow in 5 Seconds..
girls exploring physics PowerPoint Presentation
Download Presentation
girls exploring physics

girls exploring physics

118 Vues Download Presentation
Télécharger la présentation

girls exploring physics

- - - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript

  1. girls exploring physics

  2. meiosis 13 February 2012

  3. diploid • diploid number (2n): • specific number of chromosomes in eukaryotic cells • 46 for humans • Mitosis produces diploid cells

  4. haploid • haploid number (n): • number of chromosomes in a gamete • gamete: • sex cell (eg. sperm, ovum)

  5. how? • Gametes are haploid (n) cells, and mitosis forms diploid (2n) cells, so gametes cannot be formed by mitosis. • meiosis

  6. meiosis I

  7. interphase • cell growth • DNA replication • DNA loosely coiled in chromatin form • nuclear membrane intact

  8. prophase I • spindle forming • chromatin condensing into chromosomes • nuclear membrane dissolving

  9. metaphase I • pairs of chromosomes line up on opposite sides of metaphase plate • spindle attaches to individual chromosomes

  10. anaphase I • homologous chromosomes pulled away to separate ends of cell • pairs are now separated

  11. telophase I • cell begins to cleave in half • each pole of cell now has half the original number of chromosomes

  12. interkinesis • haploid cells • similar to interphase • cell growth, protein formation • no DNA replication

  13. prophase II • one chromosome of the homologous pair in each cell • chromatin condenses

  14. metaphase II • chromosomes line up at metaphase plate like in mitosis

  15. anaphase II • sister chromatids pulled apart at centromere • chromatids move to opposite poles of cell • once separate, each chromatid considered to be a chromosome

  16. telophase II • spindle fibres begin to disappear • nuclear membrane forms around each set of chromosomes

  17. cytokinesis • cells separate • now have four haploid cells

  18. meiosis is complete

  19. genetic variation • Why aren’t we identical? • Why aren’t brothers and sisters identical?

  20. independent assortment • mathematically, there are more than 8 million possible combinations of 23 chromosomes • 2×2×2×2×… = 223

  21. independent assortment • gametes combine (eg. sperm + egg) and there are more than 70 trillion possible combinations • 8 388 608 × 8 388 608 = 70 368 744 177 664

  22. more variation • crossing over • before pairs of chromosomes are separated, they can ‘trade’ segments of DNA

  23. crossing over

  24. DANCE PARTY