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Meiosis

Meiosis . Vocab Heredity – the passing of traits/genes from one generation to the next Genetics – the study of heredity Genes – segments of DNA that code for a specific trait. Cell Division / Asexual Reproduction Asexual reproduction – 1 parent ….identical offspring (clones)

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Meiosis

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  1. Meiosis

  2. Vocab Heredity – the passing of traits/genes from one generation to the next Genetics – the study of heredity Genes – segments of DNA that code for a specific trait

  3. Cell Division / Asexual Reproduction Asexual reproduction – 1 parent ….identical offspring (clones) *single celled eukaryotes…..yeast, paramecium, amoeba *simple multicellulareukaryotes...hydra, jellyfish, *binary fission……bacteria *mitosis ……identical daughter cells (clones), same # of chromosomes, same DNA budding budding

  4. Sexual reproduction – 2 parents = diff offspring + = What are the disadvantages of asexual reproduction? What are the advantages to asexual reproduction?

  5. Karyotype – picture of 23 pairs of chromosomes (46) Homologous chromosomes – identical chromosomes …same length, centromere, same staining pattern …exception…males sex chromosome 1-22 autosomes sex chromsomes

  6. Human female karyotype 46 chromosomes 23 pairs

  7. Human male karyotype 46 chromosomes 23 pairs

  8. 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

  9. 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

  10. 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

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

  12. Meiosis I – Division of homologous pairs Prophase I : -chromosomes condense & form homologous chromosomes called tetrads or bivalents -crossing over occurs forming chiasmata -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

  13. Meiosis I – Division of homologous pairs Metaphase I : -homologous pairs align at metaphase plate -kinetochore microtubules attach to one chromosome of each pair

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

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

  16. Meiosis I Animation

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

  18. Meiosis II – Division of sister chromatids Metaphase II : -chromosomes on metaphase plate -kinetochore microtubules attach to sister chromatidsof each chromosome

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

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

  21. Meiosis II Animation

  22. Meiosis I and II

  23. Meiosis 1

  24. Meiosis 2

  25. 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

  26. 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

  27. 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

  28. http://www.youtube.com/watch?v=0gF8bCE4wqA&safe=active Hela Cell http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter12/animations.html#

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