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Meiosis

Meiosis . Homologous chromosomes – identical chromosomes …same length, centromere , same staining pattern …exception…males sex chromosome 1-22 autosomes sex chromsomes. Homologous chromosomes. Paired chromosomes both chromosomes of a pair carry “matching” genes

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Meiosis

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  1. Meiosis

  2. Homologous chromosomes – identical chromosomes …same length, centromere, same staining pattern …exception…males sex chromosome 1-22 autosomes sex chromsomes

  3. Homologous chromosomes • Paired chromosomes • both chromosomes of a pair carry “matching” genes • control same inherited characters • homologous = sameinformation single stranded homologouschromosomes diploid2n 2n = 4 double strandedhomologous chromosomes

  4. 46 46 23 23 46 23 23 How do we make sperm & eggs? • Must reduce 46 chromosomes  23 egg meiosis zygote fertilization sperm Gametes – single set of 22 chromosomes 1 sex chromosome…(n)=23 gametes

  5. Meiosis: production of gametes • Happens in gonads • Conserves chromosome # • diploid haploid • 2n n • humans: 46  23 • meiosis reduces chromosome number • makes gametes • fertilization restores chromosome number • haploid  diploid • n  2n

  6. Meiosis I – Division of homologous pairs Interphase I : -G1, S, G2 *replicates only once!

  7. Meiosis I – Division of homologous pairs Prophase I : -chromosomes condense & form homologous chromosomes called tetrads or bivalents -crossing over occurs (exchange genes between homologous pairs -synapsis allows for maternal chromsomes to pair up w/ its paternal homolog -centrosomes move to poles, meiotic spindle forms -nuclear membrane disappears -90% of time

  8. Meiosis I – Division of homologous pairs Metaphase I : -homologous pairs align at the middle/equator -spindle fibers attach to kinetochore

  9. Meiosis I – Division of homologous pairs Anaphase I : -homologous chromosomes move toward opposite poles *separate the pair

  10. Meiosis I – Division of homologous pairs Telophase I & Cytokinesis : -two new nuclei form -homologous chromosomes form into chromatin -nuclear membrane reappears -divide cytoplasm

  11. Meiosis I Animation

  12. Meiosis II – Division of sister chromatids Interphase II : -G1, G2 * No replication!! Prophase II : -spindle apparatus forms -sister chromatids become visible -nuclear membrane disappears

  13. Meiosis II – Division of sister chromatids Metaphase II : -sister chromatids at metaphase plate/midline -spindle fibers attach to kinetochores on each sister chromatid

  14. Meiosis II – Division of sister chromatids Anaphase II : -sister chromatids move toward opp poles

  15. Meiosis II – Division of sister chromatids Telophase II : -nuclear membrane reforms -chromatin forms -cytokinesis produces 4 haploid (n) cells

  16. Meiosis II Animation

  17. Meiosis I and II

  18. Meiosis 1

  19. Meiosis 2

  20. http://cochrane.rockyview.ab.ca/Members/carolynjmcleod/biology-30/chapter-16-cell-division/BIO%2030%20%20SPERMATOGENESIS%20AND%20OOGENESIS%20ANIMATIONS.doc/viewhttp://cochrane.rockyview.ab.ca/Members/carolynjmcleod/biology-30/chapter-16-cell-division/BIO%2030%20%20SPERMATOGENESIS%20AND%20OOGENESIS%20ANIMATIONS.doc/view Spermatogenesis Oogenesis = 4 haploid sperm =1 egg and 3 polar bodies http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter28/animation__spermatogenesis__quiz_1_.html http://wps.aw.com/bc_martini_eap_4/40/10469/2680298.cw/content/index.html

  21. One way meiosis generates genetic variability is through the different ways in which maternal and paternal chromosomes are combined in the daughter cells. The number of possible chromosome combinations in the haploid nuclei is potentially very large. In general, the number of possible chromosome combinations is 2n, where n is the number of chromosome pairs. For example, in fruit flies, which have 4 chromosome pairs, the number of possible combinations is 2n, or 16. For humans, with 23 chromosome pairs, there are over 8 million metaphase arrangements. 2 parents = zygote : 223 x 223 = over 70 trillion

  22. 3 Sources of Genetic Variability Independent Assortment of homologous chromosome in meiosis I Crossing over during prophase I Random fertilization of egg and sperm http://www.pbs.org/wgbh/nova/body/how-cells-divide.html

  23. Differences across kingdoms • Not all organisms use haploid & diploid stages in same way • which one is dominant (2n or n) differs • but still alternate between haploid & diploid • must for sexual reproduction

  24. http://www.youtube.com/watch?v=kVMb4Js99tA http://www.youtube.com/watch?v=iCL6d0OwKt8 Meiosis Square Dance http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter12/animations.html#

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