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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
- 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) 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
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
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.
- Winter '14