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Activity 3-4 March ( Professional Studies)3A


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Activity 3-4 March ( Professional Studies)3A

  2. 2.  In humans, somatic cells (body cells) have:  23 pairs of homologous chromosomes and  one member of each pair from each parent.  The human sex chromosomes (Gonosomes) X and Y differ in size and genetic composition.  The other 22 pairs of chromosomes are autosomes with the same size and genetic composition. © 2012 Pearson Education, Inc.
  3. 3. Homologous chromosomes are matched in: • length,  centromere position, and  gene locations (locus).  A locus is the position of a gene.  Different versions alleles of a gene may be found at the same locus on maternal and paternal chromosomes. © 2012 Pearson Education, Inc.
  4. 4. Fig. 13-3b TECHNIQUE 5 µm Pair of homologous replicated chromosomes Centromere Sister chromatids Metaphase chromosome
  5. 5.  All organisms have different numbers of chromosomes.  A body cell in an adult fruit fly has 8 chromosomes: 4 from the fruit fly's male parent, and 4 from its female parent.
  6. 6. These two sets of chromosomes are homologous. Each of the 4 chromosomes that came from the paternal has a corresponding chromosome from the maternal
  7. 7. A cell that contains both sets of homologous chromosomes is said to be diploid. The number of chromosomes in a diploid cell is sometimes represented by the symbol (2n)
  8. 8.  Meiosis is a process that converts diploid nuclei to haploid nuclei.  Diploid cells have 2 sets of chromosomes.  Haploid cells have 1 set of chromosomes.  Meiosis occurs in the sex organs, producing gametes—sperm and eggs.  Fertilization is the fusion of a sperm and egg cell.  The zygote has a diploid chromosome number, one set from each parent. © 2012 Pearson Education, Inc.
  9. 9. What happens during the process of meiosis?
  10. 10. Meiosis involves two divisions, meiosis I and meiosis II. By the end of meiosis II, the diploid cell that entered meiosis has become 4 haploid cells.
  11. 11. Meiosis Interphase I I Prophase I Metaphase I Anaphase I Telophase I and Cytokinesis
  12. 12. Interphase I Cells undergo a round of DNA replication, forming duplicate chromosomes.
  13. 13. MEIOSIS I: Prophase I  Each chromosome pairs with its corresponding homologous chromosome to form a tetrad.  There are 4 chromatids in a tetrad.
  14. 14. When homologous chromosomes form tetrads in meiosis I, they exchange portions of their chromatids in a process called crossing over. Crossing-over produces new combinations of alleles.
  15. 15. MEIOSIS I: Metaphase I Spindle fibers attach to the chromosomes.
  16. 16. MEIOSIS I: Anaphase I The fibers pull the homologous chromosomes toward opposite ends of the cell.
  17. 17.  Nuclear MEIOSIS I: Telophase I and Cytokinesis membranes form.  The cell separates into two cells.  The two cells produced by meiosis I have chromosomes and alleles that are different from each other and from the diploid cell that entered meiosis I.
  18. 18. MEIOSIS ll The two cells produced by meiosis I now enter a second meiotic division. Unlike meiosis I, neither cell goes through chromosome replication. Each of the cell’s chromosomes has 2 chromatids.
  19. 19. Meiosis II Telophase I and Cytokinesis I Meiosis II Prophase II Metaphase II Anaphase II Telophase II and Cytokinesis
  20. 20. MEIOSIS II: Prophase II Meiosis I results in two haploid (n) daughter cells, each with half the number of chromosomes as the original cell.
  21. 21. MEIOSIS II Metaphase II The chromosomes line up in the center of cell.
  22. 22. MEIOSIS II Anaphase II  The sister chromatids separate and move toward opposite ends of the cell.
  23. 23. MEIOSIS II Telophase II and Cytokinesis  Meiosis II results in four haploid (n) daughter cells
  24. 24. In male animals, meiosis results in four equal-sized gametes called sperm.
  25. 25. In many female animals, only one egg results from meiosis. The other three cells, called polar bodies, are usually not involved in reproduction.
  26. 26. MITOSIS • Cells produced by mitosis have the same number of chromosomes and alleles as the original cell. • Mitosis allows an organism to grow and replace cells. • Some organisms reproduce asexually by mitosis.
  27. 27. MEIOSIS Cells produced by meiosis have half the number of chromosomes as the parent cell. These cells are genetically different from the diploid cell and from each other. Meiosis is how sexually-reproducing organisms produce gametes.
  28. 28.  Cayey,C.U (2013), The Cycle.  Feder, A. (2013).  Gquinnn617,(2014), Median Genetics and meiosis.  Rozeka, P. (2013). Biology, cell division meiosis. Swan,J. (2011). Meiosis and Sexual Life Cycle.