Lecture_15_LODs_&_Tetrads_2011 (1)

Lecture_15_LODs_&_Tetrads_2011 (1) - LODs...

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LODs &Tetrad Analysis Feb. 16 th 2011
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Announcements 3 rd problem set due Friday at 4:00 pm.
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Review TWO-POINT TEST CROSS data can be combined to generate a map of multiple genes. THREE-POINT TEST CROSS data is more accurate because it can detect double crossovers. CHI SQUARE can be used to determine if alleles are randomly segregating and distinguish between linkage and independent assortment. CROSSOVER INTERFERENCE can depress the expected frequency of double crossovers .
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Human families vs. model crosses Not enough progeny!
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LOD Scores tands for L og O f O dds log(p(specific linkage value)/p(independent assortment)) probabilities derived from pedigree analysis D suggests linkage icists use a LOD of 3 as an arbitrary cut-off for significance 3 means that linkage is 1000 more times more likely than n cores can be additive – scores from multiple families can be 3 - 2 - 1 - | | | | | | | | | | | | | |
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LOD Example Aa·Bb aa·bb Aa·Bb aa·BB Aa·BB Aa·BB aa·Bb Which progeny Are recombinant?
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Aa·Bb aa·bb Aa·Bb aa·BB Aa·BB Aa·BB aa·Bb LOD Example cont. had to come from ♀ ab had to come from ♂
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Aa·Bb aa·bb Aa·Bb aa·BB A a ·B B A a ·B B a a · B b LOD Example cont. had to come from ♀ AB had to come from ♂ Will give all progeny aB
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Aa·Bb aa·bb Aa·Bb aa·BB A a ·B B A a ·B B a a · B b LOD Example cont. had to come from ♀ AB had to come from ♂ Will give all progeny aB So all progeny are Nonrecombinant Is this due to linkage or independent assortment?
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LOD Example cont. termine p(observed results w/ independent assortment) he two loci are assorting independently then all four progeny classes will be represented equally (25%) erefore the probability of the observed results if unlinked is: 25)(0.25)(0.25) = 0.016 Aa·Bb aa·BB X A a
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Lecture_15_LODs_&_Tetrads_2011 (1) - LODs...

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