PS2A KEY - BICD100 Genetics Winter 2008 Problem Set 2A...

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Problem Set 2A Linkage and mapping (A separate problem set will be made for tetrad analysis) 1. In a plant, leaf color and leaf shape are controlled by two linked genes. Leaves of the wild-type plant are red. A recessive mutation in this gene causes white leaves. Wild- type leaves are pointed, and a recessive mutation in this gene causes them to be smooth. The following crosses were performed: Cross 1: pure breeding white, smooth X pure breeding wild type gives F1: all red, pointed Cross 2: red, pointed F1 X pure breeding white, smooth (test cross) gives F2: 40 white, smooth 36 red, pointed 10 white, pointed 14 red, smooth a) What is the recombination frequency between the genes for color and shape? RF = Recombinants/Total = (10+14)/100 = 24% = 24 cM b) Using Haldane’s mapping function 2x = -ln[1-2RF] calculate the map distance x in centiMorgans. Comment on the applicability of the mapping function in this experiment. Using the mapping function we get map distance = 0.32 Morgans (32 cM) The RF is an underestimate of the map distance due to double crossovers. 2. Gregor Mendel’s less well known brother Fritz embarked on yet another series of pea breeding experiments. Peas can be either rough or smooth, and either soft or hard. Fritz crosses true-breeding rough soft peas with true-breeding smooth hard peas and find all the F1 are rough hard peas. Fritz then crosses these F1 peas with smooth soft peas and finds in the F2: 115 rough soft Rh/rh (Rh from F1 parental gamete) 110 smooth hard rH/rh (rH from F1 parental gamete) 8 rough hard RH/rh (RH from F1 recombinant gamete) 12 smooth soft rh/rh (rh from F1 recombinant gamete) Fritz is puzzled by these results and asks your advice. a) Using letters of your own choosing, write out the genotypes of the parents, F1s and the F2 classes. Use lines to indicate linkage. Use Rr for rough/smooth and Hh for hard/soft. Parents = Rh/Rh and rH/rH (best to use this notation since linkage is apparent from inspection). F1 = Rh/rH (dihybrids) crossed with rh/rh (test cross). F2s above. b) Are the genes for roughness and hardness linked? If so what is the approximate map distance (do not use the mapping function). The genes are linked (parentals > recombinants). RF = 20/245 = 0.0816 BICD100 Genetics Winter 2008 Problem Set 2A Chisholm 1
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Multiply by 100 to get map distance in centiMorgans = 8.1% 3. First officer Spock of the Starship Enterprise had a Vulcan father and an Earthling mother. The alleles affecting the Vulcan traits of pointed ears (P), no adrenal glands (A) and right-sided heart (R) are autosomal and dominant to the earth alleles. The three genes are linked in the order P--A--R. The recombination frequency between P and A is 15% and the recombination frequency between A and R is 20%. If Spock married an Earth woman and they had children, and assuming there is no interference, calculate the probability that their child will be: a. Vulcanian for all three characters. This would be due to a nonrecombinant gamete from Spock.
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This note was uploaded on 06/07/2008 for the course BICD 100 taught by Professor Nehring during the Winter '08 term at UCSD.

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PS2A KEY - BICD100 Genetics Winter 2008 Problem Set 2A...

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