Introduction to Genetic Analysis 135

Introduction to Genetic Analysis 135 - 134 Chapter 4...

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Unformatted text preview: 134 Chapter 4 Eukaryote Chromosome Mapping by Recombination The probability of obtaining the results under indepen- dent assortment (RF of 50 percent) will be equal to 0.25 3 0.25 3 0.25 3 0.25 3 0.25 3 0.25 3 B 5 0.00024 3 B where B 5 the number of possible birth orders for four parental and two recombinant individuals. For an RF of 0.2, the probability is 0.4 3 0.1 3 0.4 3 0.4 3 0.1 3 0.4 3 B 5 0.00026 3 B The ratio of the two is 0.00026/0.00024 5 1.08 (note that the Bs cancel out). Hence, on the basis of these data, the hypothesis of an RF of 0.2 is 1.08 times as likely as the hypothesis of independent assortment. Finally, we take the logarithm of the ratio to obtain the Lod value. Some other ratios and their Lod values are shown in the following table: will look at two methods. First we examine a method originally worked out by J. B. S. Haldane in the early years of genetics. A mapping function The approach worked out by Haldane was to devise a mapping function, a formula that relates RF value to real physical distance. An accurate measure of physical distance is the...
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