The A and B genes are 10 cM apart on a chromosome. If an AB/ab heterozygote is testcrossed to ab/ab, how many

Evaluation · Q2

Q. The A and B genes are 10 cM apart on a chromosome. If an AB/ab heterozygote is testcrossed to ab/ab, how many of each progeny class would you expect out of 100 total progeny?

a) 25 AB, 25 ab, 25 Ab, 25 aB

b) 10 AB, 10 ab

c) 45 AB, 45 ab

d) 45 AB, 45 ab, 5 Ab, 5 aB

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✓ Free question

Step 1. Recombination frequency (RF) is the percentage of recombinant progeny out of the total; here RF = 10 cM = 10%.

Step 2. Of the 10% recombinants, the two recombinant classes (Ab and aB) each get half: 5% each, i.e. 5 out of 100.

Step 3. The remaining 90% are parental types (AB and ab), split evenly: 45% each, i.e. 45 out of 100.

✓Final answer

Out of 100 progeny, the expected classes are 45 AB, 45 ab, 5 Ab and 5 aB, option (d).

Q.The A and B genes are 10 cM apart on a chromosome. If an AB/ab heterozygote is testcrossed to ab/ab, how many of each progeny class would you expect out of 100 total progeny?