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    Meiotic Nondisjunction

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    Meiotic nondisjunction events will create aneuploid gametes. Describe (with figures) normal Drosophila male meiotic segregation of the sex chromosomes. Then describe all possible outcomes if a Meiosis-I nondisjunction occurs; then do the same for Meiosis-II nondisjunction.

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    Please see response and corresponding figures attached.

    1. Meiotic nondisjunction events will create aneuploid gametes. Describe (with figures) normal Drosophilae male meiotic segregation of the sex chromosomes.

    In a normal meiosis (Figure 5A) (http://www.mcb.ucdavis.edu/courses/w04/bis101-03/pdfs/Lecture16fig10.pdf) the homologs synapse during meiotic prophase and form a chiasma. When both homologs are then attached to opposite poles of the spindle, tension is generated. This tension signals that the spindle is attached correctly. Meiosis I can proceed when the chiasma is resolved and sister cohesion is dissolved distal of the chiasma point. Meiosis II proceeds when the spindle is set up correctly to bring each chromosome (with the two sisters) under tension, because the centromeres are still linked through cohesion. Tension signals the attachments to the spindle is correct (both sister chromatids to opposite poles), and then cohesion is completely dissolved, so that Meiosis II anaphase can proceed.

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    Solution Summary

    Meiotic nondisjunction events will create aneuploid gametes. This solution describes (with figures) normal Drosophila male meiotic segregation of the sex chromosomes. It then describes all possible outcomes if a Meiosis-I nondisjunction occurs and then does the same for Meiosis-II nondisjunction. Supplemented with a diagram.

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