Use the following information to answer the questions below.
A plantlike organism on the planet Pandora can have three recessive genetic traits: bluish leaves, due to an allele (a) of gene A; a feathered stem, due to an allele (b) of gene B; and hollow roots due to an allele (c) of gene C. The three genes are linked and recombine as follows:
A geneticist did a testcross with an organism that had been found to be heterozygous for the three recessive traits and she was able to identify progeny of the following phenotypic distribution (+ = wild type):

-If recombination is equal to distance in centimorgans (cM), what is the approximate distance between genes A and B?
A) 1.5 cM
B) 3 cM
C) 6 cM
D) 15 cM
E) 30 cM

Question

Use the following information to answer the questions below.
A plantlike organism on the planet Pandora can have three recessive genetic traits: bluish leaves, due to an allele (a) of gene A; a feathered stem, due to an allele (b) of gene B; and hollow roots due to an allele (c) of gene C. The three genes are linked and recombine as follows:
A geneticist did a testcross with an organism that had been found to be heterozygous for the three recessive traits and she was able to identify progeny of the following phenotypic distribution (+ = wild type):
 
-If recombination is equal to distance in centimorgans (cM), what is the approximate distance between genes A and B?
A) 1.5 cM 
B) 3 cM 
C) 6 cM 
D) 15 cM 
E) 30 cM

Quizplus · Accepted Answer

The progeny show 11 recombinant types out of the total of 32. This means that the recombination frequency is 11/32 or 0.344. Since there are two meiotic events involved (A&B, and B&C), we need to divide this number by 2 to get the recombination frequency per interval. Thus, the distance between A and B is approximately 0.344/2, or 0.172 cM. Rounded to the nearest whole number, this is 3 cM.

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