Textbook Notes (369,144)
United States (206,213)
Biology (392)
CAS BI 108 (112)
Chapter 11.5

Chapter 11.5 Notes

3 Pages

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CAS BI 108
Francis Monette

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BI108 Chapter 11 Notes: The Cell Cycle and Cell Division 11.5: What Happens During Meiosis? Two nuclear divisions that reduce the number of chromosomes to haploid number. Although the nucleus divides twice, the DNAis only replicated once. Overall Functions:  Reduce chromosome number from diploid to haploid  Ensure that each of the haploid products has a complete set of chromosomes  Generate genetic diversity among products Meiotic division reduces the chromosome number Meiosis I:  Homologous chromosomes come together and then separate (but remember that the sister chromatids remain intact)  Preceded by S phase—each chromosome is replicatedtwo sister chromatids held together by cohesin proteins  At the end, two nuclei form, and each has half of the original chromosomes (one member of each homologous pair) Sister chromatids will then be separated during Meiosis II Meiosis I Early Prophase Mid-Prophase Late Prophase-Prometaphase Metaphase Anaphase Telophase Meiosis II Prophase II Prometaphase II Anaphase II Telophase II Products Chromatid exchanges during meiosis I generate genetic diversity Synapsis: homologous chromosomes pair by adhering along their lengths. This process lasts from prophase I to the end of metaphase I. Note: the four chromatids of each pair of homologous chromosomes form a tetrad.At the end of prophase one the human cell contains 23 tetrads (each has four chromatids) Chiasmata: regions where homologous chromosomes are attached, they have an X-shaped appearance. BI108 Chapter 11 Notes: The Cell Cycle and Cell Division  The chiasmata reflects an exchange of genetic material between nonsister chromatids on homologous chromosomes. This process is called crossing over.  Material is exchanged and later the homologs repel each other  Crossing over results in recombinant chromosomes. It also increases genetic variation by shuffling info among the homologous pairs. During meiosis homologous chromosomes separate by independent assortment Diploid: (2n) = 2 sets of chromosomes; one from male parent, one from female parent.As the organism grows, its cel
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