PS7_Key - BICD100 Genetics Fall 2005 Problem Set 7 =...

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BICD100 Genetics Fall 2005 Prof. Reinagel Problem Set 7 = Practice Midterm 2 1. You are studying three autosomal recessive mutations in Drosophila that are linked: mangy, nervous, and ornery. You obtain flies from a pure breeding mangy, nervous, and ornery strain and cross to wild type flies to obtain an F1. You then cross the F1 flies to flies from the pure breeding mangy, nervous, and ornery strain to obtain the following F2: Phenotype Number of F2 flies m-o o-n m-n mangy, nervous, ornery 2119 par par par mangy, nervous 3 DCO (rare) non non par mangy, ornery 342 par non non nervous, ornery 20 non par non mangy 23 non par non nervous 351 par non non ornery 4 DCO (rare) non non par wild type 2138 par par par 5000 total Derive the most accurate map you can of the order of these genes and the distances between them. 2 valid ways to solve: either use rare class to infer which is in the middle, as shown, or solve all three pairwise distances and then infer the best linear map. ornery in middle (rare DCO class) m-o distance = 3+20+23+4 x 100 = 1 cM 5000 o-n distance = 3+342+351+4 x 100 = 14 cM 5000 m-n distance (not required if you already have the map order) = 342+20+23+351 x 100 = 14.7 cM 5000 answer: m o n --|-------|----------|------- 1 14 You were not asked to determine interference.
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BICD100 Genetics Fall 2005 Prof. Reinagel 2. You cross two haploid yeast strains cdc10 leu1 trp5 X cdc+ leu+ trp+ to obtain a triply heterozygous diploid. The cdc10 gene is tightly linked the centromere of chromosome III. The leu1 and trp5 genes are both located on the same arm of chromosome VII, with leu1 closer to the centromere than trp5. For each of the following types of tetrads, diagram the 4-chromatid stage of meiosis producing a tetrad of the type specified. The diagram should show the location(s) of crossover(s) if any, and clearly indicate which chromatids segregate together in order to explain the genotypes of the 4 spores. For full credit you must show the minimum number of crossovers that could explain the tetrad type. If there is more than one way to obtain the specified tetrad type using the same number of crossover events, show only one example. a) TT for cdc10 and trp5 The two genes are unlinked, and cdc10 is centromere linked, so TT arises from a crossover between trp5 and its centromere, for example: ---.---leu1---trp5-- --.cdc10---------- ---.---leu1---trp5-- --.cdc10----------    X ===.===LEU+===TRP+== ==.CDC+=========== ===.===LEU+===TRP+== ==.CDC+===========   b) NPD for cdc10 and leu1 The two genes are unlinked, so no crossovers are required, just segregation: ---.---leu1---trp5-- ==.CDC+=========== ---.---leu1---trp5-- ==.CDC+=========== ===.===LEU+===TRP+== --.cdc10---------- ===.===LEU+===TRP+== --.cdc10----------
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BICD100 Genetics Fall 2005 Prof. Reinagel c) NPD for leu2 and trp5 The genes are linked, so only a 4-strand double crossover can produce an NPD, for example: ---.---leu1---trp5-- ==.CDC+=========== ---.---leu1---trp5-- ==.CDC+===========
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This note was uploaded on 02/23/2010 for the course BICD bicd 100 taught by Professor Soowal during the Spring '08 term at UCSD.

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PS7_Key - BICD100 Genetics Fall 2005 Problem Set 7 =...

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