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  4. 4. 5.2 MEIOSIS<br />7th May 2010<br />
  5. 5. What is meiosis?<br />The process of nuclear division that reduces the number of chromosomes in new cells to half the number of chromosomes in parent cell.<br /> 2n (diploid) [parent cell]<br /> n (diploid) [new cell]<br />
  6. 6. Necessity of trait inheritance<br />SEXUAL REPRODUCTION<br />Involves:<br />Fusion of TWO haploid gametes<br />Results in :<br />Formation of a DIPLOID zygote.<br />Means:<br />Offspring (child) will inherit traits from both parents to continue life.<br />n<br />n<br />2n<br />
  7. 7. The Significance of MEIOSIS<br />Sexual reproduction leads to genetic variation among the offspring.<br />Meiosis makes genetic variations possible in three ways:<br />Cross-over<br />Reduction and fusion of gametes<br />Independent (random) assortment<br />
  8. 8. Where does Meiosis Takes Place?<br />Human<br />Testes (male)<br />Ovaries (female)<br />Plant<br />Anthers <br />Ovaries <br />Flowers <br />
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  10. 10. Stages of MEIOSIS<br />Consists of TWO separate divisions:<br /><ul><li> Meiosis I
  11. 11. Meiosis II
  12. 12. Begins with single diploid parent cell.
  13. 13. Prophase I, Metaphase I, Anapphase I, Telophase I
  14. 14. At the end, four haploid daughter cells produced.
  15. 15. Prophase II, Metaphase II ,Anaphase II, Telophase II</li></ul>MEIOSIS I<br />MEIOSIS II<br />
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  18. 18. Interphase<br />Before meiosis begins, genetic material is duplicated.<br />At this point, chromosomes are not condensed and are not visible under a light microscope.<br />
  19. 19. MEIOSIS I: Prophase I <br />Duplicated chromatin condenses. Each chromosome consists of two, closely associated sister chromatids. <br />Cell has two centrosomes, which form the mitotic spindle.<br />The pairing is called  synapsis.<br />Nuclear envelop breaks down.<br />Crossing-over can occur during the latter part of this stage. Crossing-over point  chiasmata<br />Diploid cell contains homologous chromosomes. One chromosome in each pair is maternally derived and one is paternally derived.<br />
  20. 20. Homologous chromosomes lined up at equatorial plate in a pair-wise fashion.<br />MEIOSIS I: Metaphase I <br />
  21. 21. Homologous pairs separate with sister chromatids remaining together. <br />The centromeres of the chromosomes do not, so each chromosome still consists of two sister chromatids, which now may not be genetically identical due to crossing over.<br />MEIOSIS I: Anaphase I <br />
  22. 22. Two daughter cells are formed with each daughter containing only one chromosome of the homologous pair.<br />Interkinesis (a short period of interphase) then follow telophase I.<br />DNA replication does not take place during interkinesis. <br />MEIOSIS I: Telophase I <br />
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  25. 25. 5.2 SELF TEST<br />1) _________ cells contain two copies of each chromosome.<br />a) haploid<br />b) diploid <br />c) aneuploid<br />d) homologous <br />2) In general, gametes are ___________ and somatic cells are ____________. <br />a) diploid, haploid<br />b) haploid, diploid<br />c) diploid, diploid <br />d) haploid, haploid <br />
  26. 26. 3) Pairs of matching chromosomes are termed ______________, and each member of the pair is called a _____________. <br />a) paired, haploid <br />b) diploid, haploid <br />c) homologous chromosomes, homolog <br />d) homolog, homologous chromosomes <br />4) Which of the following represent the correct sequence of steps in meiosis?<br />a) telophase, metaphase, anaphase, prophase<br />b) anaphase, metaphase, telophase, prophase <br />c) prophase, metaphase, anaphase, telophase<br />d) metaphase, anaphase, prophase, telophase<br />
  27. 27. 5) What structures separate from one another during meiosis I? <br />a) sister chromatids<br />b) homologous chromosomes <br />c) centromeres<br />d) Synapsis<br />6) During what stage of meiosis I does synapsis occur? <br />a) prophase <br />b) metaphase <br />c) anaphase <br />d) telophase<br />
  28. 28. 7) During what stage of meiosis I does crossing over occur? <br />a) prophase <br />b) metaphase <br />c) anaphase <br />d) telophase<br />8) Human males have <br />a) 22 pairs of autosomes and two X chromosomes <br />b) 22 pairs of sex chromosomes and 1 pair of autosomes<br />c) 22 pairs of autosomes, one X chromosome and one Y chromosome<br />d) 1 pair of autosomes and two X chromosomes <br />
  29. 29. 9) State fivesimilarities and fivedifferences between mitosis and meiosis.<br />Similarities <br />1. Both involve cell divisions<br />2. Both start from diploid cells<br />3. Chromosomes duplicate only once<br />4. Both involve the separation of chromatids in<br /> anaphase of mitosis and in anaphase II<br />5. Both follow similar phases: prophase, metaphase,<br /> anaphase and telophase.<br />
  30. 30. Differences <br />