Question

Genes C and D are linked with a recombination frequency of 0.4. Both genes segregate dominant (C and D) and recessive alleles (c and d). The parental cross CCDD x ccdd is performed and then the F1 progeny is testcrossed to ccdd. If 10 individuals are counted in the F2, how many are expected to be dominant for BOTH genes?

a) 0
b) 1
c) 2
d) 4
e)none of these

Answer 1

If 10 individuals are counted in the F2 generation resulting from a testcross between F1 progeny (CcDd) and ccdd, it is expected that 6 individuals would be dominant for BOTH genes.

Step-by-step explanation:

In this case, the parental cross CCDD x ccdd results in all F1 progeny having the genotype CcDd.

Since genes C and D are linked with a recombination frequency of 0.4, it means that there is a 40% chance of recombination occurring between these two genes during gamete formation.

Therefore, if the F1 progeny (CcDd) is testcrossed to ccdd, we would expect 40% of the offspring in the F2 generation to have at least one recombination event between genes C and D. Since we are interested in individuals that are dominant for BOTH genes, we would expect 60% of the offspring to NOT have any recombination between genes C and D.

If 10 individuals are counted in the F2, then 60% of 10 is 6. Therefore, we would expect 6 individuals to be dominant for BOTH genes.