BIOL 2500 Lecture Notes - Lecture 10: Heterogametic Sex, Meiosis, Aneuploidy
20 May 2016
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Document Summary
Upper limit to recombinant gametes - double crossovers. There are three possible patterns of double crossovers. Two - strand double crossovers produce only parental gametes. Three - strand double crossovers produce 50% parental and 50% recombinant gametes. Four - strand double crossovers produce all recombinant genes. Age, environment, and sex may affect recombination. In female fruit ies, increased age decreases recombination frequency. Fruit ies grown at temperatures above or below optimal 22 degrees celsius experience changes in recombination frequency. Levels of dietary calcium and magnesium also affect rates of crossover in ies. Recombination rates differ between males and females for most animals. The heterogametic sex generally has a lower recombination rate than the homogametic sex. The differences in recombination rate are genome-wide, i. e. , not con ned to the sex chromosomes. In male fruit ies, there is no crossing over at all. Euploid (n, 2n, 3n ect) considered the norm.
