1. SEXUAL REPRODUCTION AND GENETICS MEIOSIS

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. 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. Fig. 13-3bTECHNIQUE 5 m Pair of homologous replicated chromosomes CentromereSister chromatids Metaphase chromosome 5. Allorganisms 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. Thesetwo sets of chromosomes are homologous. Each of the 4 chromosomes that came from the paternal has a corresponding chromosome from the maternal 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. Meiosis is a process that converts diploidnuclei to haploid nuclei. Diploid cells have 2 sets of chromosomes. Haploid cells have 1 set of chromosomes. Meiosis occurs in the sex organs, producing gametessperm and eggs. Fertilization is the fusion of a sperm and egg cell. The zygote has a diploid chromosomenumber, one set from each parent. 2012 Pearson Education, Inc. 9. Whathappens during the process of meiosis? 10. Meiosisinvolves 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. MeiosisInterphase IIProphase IMetaphase IAnaphase ITelophase I and Cytokinesis 12. Interphase I Cellsundergo a round of DNA replication, forming duplicate chromosomes. 13. MEIOSIS I: Prophase I Eachchromosome pairs with its corresponding homologous chromosome to form a tetrad. There are 4 chromatids in a tetrad. 14. Whenhomologous 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. MEIOSIS I: Metaphase I Spindle fibers attach to the chromosomes. 16. MEIOSIS I: Anaphase I Thefibers pull the homologous chromosomes toward opposite ends of the cell. 17. NuclearMEIOSIS I: Telophase I and Cytokinesismembranes 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. MEIOSIS ll Thetwo cells produced by meiosis I now enter a second meiotic division. Unlike meiosis I, neither cell goes through chromosome replication. Each of the cells chromosomes has 2 chromatids. 19. Meiosis IITelophase I and Cytokinesis IMeiosis II Prophase IIMetaphase IIAnaphase II Telophase II and Cytokinesis 20. MEIOSIS II: Prophase II MeiosisI results in two haploid (n) daughter cells, each with half the number of chromosomes as the original cell. 21. MEIOSIS II Metaphase II Thechromosomes line up in the center of cell. 22. MEIOSIS II Anaphase II Thesister chromatids separate and move toward opposite ends of the cell. 23. MEIOSIS II Telophase II and Cytokinesis MeiosisII results in four haploid (n) daughter cellshttp://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/0072437316/120074/bio19.swf::Stages%20of%20Meiosis 24. Inmale animals, meiosis results in four equal-sized gametes called sperm. 25. Inmany female animals, only one egg results from meiosis. The other three cells, called polar bodies, are usually not involved in reproduction. 26. MITOSIS Cells produced by mitosis have thesame 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. MEIOSIS Cells produced by meiosis have half thenumber 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. Cayey,C.U (2013), The Cycle. http://www.slideshare.net/caecayey/cap-12-ciclocelular Feder, A. (2013). http://www.slideshare.net/jojatk/meiosisglencoe?qid=62b29050-df7e-4e20-a3589aec8af199ae&v=qf1&b=&from_search=12 Gquinnn617,(2014), Median Genetics and meiosis. http://www.slideshare.net/gquinn617/09-genetics?qid=62b29050-df7e-4e20a358-9aec8af199ae&v=qf1&b=&from_search=6 Rozeka, P. (2013). Biology, cell division meiosis. http://www.slideshare.net/rozeka01/biology-unit-4-cell-division-meiosisnotes?qid=62b29050-df7e-4e20-a3589aec8af199ae&v=qf1&b=&from_search=10 Swan,J. (2011). Meiosis and Sexual Life Cycle. http://www.slideshare.net/jayswan/chapter-12-presentation-6504580