BICD100 Problem Set 3 KEY

BICD100 Problem Set 3 KEY - BICD100 Genetics Winter 2008...

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Problem Set 3B Chromosome variation (lectures 14, 15) 1. A corn plant is heterozygous for a reciprocal translocation and is semi-sterile. You cross this plant with a non-translocation homozygote for a recessive mutation b (brachytic) on chromosome 2. You obtain a semi-sterile F1 and backcross it to the homozygous brachitic srain. In the F2 you find the following: 334 semi-sterile non-brachytic 27 fertile non-brachytic 42 semisterile brachytic 279 fertile brachytic Does the translocation include chromosome 2? Justify your answer, showing all crosses and chromosomes of progeny classes. (Hint: work out the segregation ratios for the two cases: either chromosome 2 is part or is not part of the translocation.) Remember semi sterility is telling you that the plant is a translocation het. A cross between translocation het and normal should give 1/2 translocation hets and half fertile. If 2 is not part of translocation, the brachytic mutation should be unlinked to the translocation. We should see independent assortment and 1:1:1:1 ratios in the test cross. The numbers are clearly not 1:1:1:1 (no need for a chi-squared, it is obvious). Therefore chromosome 2 is part of the translocation. If chromosome 2 is part of the translocation we will get the parental classes (brachytic fertile) and nion-brachytic semisterile. The fertile non-brachytics and semisterile brachytics are the result of recombination between the translocated chromosome and the b mutation. The RF = (27+42)/Total = 10%. This is the
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This note was uploaded on 09/08/2008 for the course BICD 100 taught by Professor Nehring during the Winter '08 term at UCSD.

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BICD100 Problem Set 3 KEY - BICD100 Genetics Winter 2008...

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