18 eg f1 gametes of wymwym female po po y w m y w m

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Unformatted text preview: + y w m 19 The number of individuals in the recombinant phenotype classes varies with how closely the genes are linked The number in the recombinant class will always be less than the number in the parental class if the genes are linked 20 Pedigrees are used to study linkage in humans Nail-patella syndrome - gene is linked to I gene of ABO blood group BO* and OO* are recombinants. 21 Pedigrees are used to study linkage in humans 22 Linkage is never 100% If you observe enough offspring, you will always see recombinant phenotypes, even if 2 genes are directly adjacent to one another. crossover events are random accidents 23 The distances between genes is indicated by recombination frequency. From the following, which gene pairs are closest? A B = 15% B C = 4% a)  A and B are closest b) B and C are closest 24 Shown are the offspring of the testcross a+b+/ab x ab/ab. Can you tell which offspring are in the parental class? a+ b+ 113 a b+ 117 a+ b 92 ab 97 a) a+b+ (113) and a b+ (117) b) a+ b (92) and ab (97) c) a+b+ (113) and ab (97) d) a b+ (117) and a+ b c (92) e) cannot tell 25 Because of chance, numbers of F2 progeny will not always give you expected ratios If genes are unlinked (on diff chromosomes), expect: If linked, expect: 50-50 ratio. same numbers parental class really outnumbers the recombinant class. sometimes they aren’t so different though… 26 Because of chance, numbers of F2 progeny will not always give you expected ratios 75 82 63 65 P numbers are not all that different. R 27 The Chi Square Test A statistical test, which can be used to evaluate hypotheses that two genes assort independently or are genetically linked Indicates how often an experimentally observed deviation from a particular hypothesis will occur solely by chance Comparison between observed and predicted values Requires LARGE sample sizes 28 The Chi Square Test When geneticists want to determine if two genes are linked, they actually test whether the data are consistent with a null hypothesis of no linkage If the chi square test shows that the observed data differ significantly from what would be expected with independent assortment, the null hypothesis is rejected. In other words, the genes are linked! 29 The Chi Square Test 1.Use the data o...
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This document was uploaded on 02/25/2014.

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