Introduction to Genetic Analysis 132

Introduction to Genetic Analysis 132 - 44200_04_p115-150...

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131 4.4 Using the chi-square test in linkage analysis some blocks of two . Some data from an actual cross of A ± a are shown in the table below. Octads Aa A a A a A a A a Aaa A a A A a A aA A a a A A a a A aAa A A a 126 132 9 11 10 12 Total ² 300 a A A a A a The first two columns are from meioses with no crossover in the region between the A locus and the centromere. These are called first-division segregation patterns (M I patterns) because the two different alleles segregate into the two daughter nuclei at the first divi- sion of meiosis. The other four patterns are all from meiocytes with a crossover. These patterns are called second-division segregation patterns (M II ) because, as a result of crossover in the centromere-to-locus region, the A and a alleles are still together in the nuclei at the end of the first division of meiosis (Figure 4-15). There has been no first division segregation. However, the second meiotic division does move the A and a alleles into sepa- rate nuclei. Figure 4-15 shows how one of these M
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