EXAM2_Practice_Problems_Key

EXAM2_Practice_Problems_Key - BLY302 FALL 2010 PRACTICE...

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BLY302 FALL 2010 PRACTICE PROBLEMS FOR EXAM 2 Q1 If the recombination frequency between genes ( A ) and ( B ) is 5.3%, what is the distance between the genes in map units on the linkage map? ANSWER: This recombination frequency is small, which indicates these gene loci are fairly close together on the chromosome. Because map distance is defined as the recombination frequency between two loci, the genetic distance between these genes is 5.3 cM. Q2 Assume that the coefficient of coincidence (CC) for a map distance of 24 cM = 0.25. Consider the following 3-factor (trihybrid) testcross: + + c (x) abc/abc a b + 10.6 cM 13.4 cM Calculate the number of progeny in each phenotype class (parentals, SCOs, and DCOs) resulting from this cross. Base your calculations on a total of 1000 progeny. Hint: The actual frequency of double-crossover progeny can be determined by multiplying the frequencies of recombination for each single crossover together (to calculate expected DCOs), and then multiplying that product by the coefficient of coincidence for the known map distance between the alleles (to calculate the actual, observed DCOs). Remember that CC = DCO obs / DCO exp ; and crossover Interference ( I ) = 1 – CC. These parameters are not just obscure concepts, they are closely related and can have very practical applications such as predicting the percentage of double-crossover progeny in a given cross. (1) The recombination frequency between genes A—B = 10.6% = 0.106 (2) The recombination frequency between genes B—C = 13.4% = 0.134 (3) Calculate the expected number of double-crossover progeny: (0.106)(0.134) = 0.0142 = expected DCO frequency (0.0142)(1000) = DCO exp = 14.2 individuals (4) CC = DCO obs / DCO exp . Therefore, DCO obs = (0.25)(14.2) = 3.55 4. This means that of 1000 progeny, you will see four double-crossover phenotypes.
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BLY302 FALL 2010 (5) Now you need to determine the numbers of progeny for each single crossover. Number of progeny (phenotypes) displaying a SCO between
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This note was uploaded on 01/05/2011 for the course BLY 302 taught by Professor Unknown during the Fall '10 term at S. Alabama.

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EXAM2_Practice_Problems_Key - BLY302 FALL 2010 PRACTICE...

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