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

3 individuals.

Explanation: Recombination frequency is the proportion of offspring who will inherit the recombinant genes.

The F1 progeny has genotype CcDd. When crossed with an individual with genotype ccdd, F2 generation can be CcDd or ccdd in a 50/50 probability.

The recombinant frequency is 0.4, which means in a total of 10 individuals of F2, 4 will be recombinant, so 6 will be parental, i.e., will carry the same genes of their parents.

From the population of 6, half of them will carry dominant genes for both features, so:

6 x 0.5 = 3

Therefore, from 10 individuals of F2, we expected 3 to be dominant for both genes.

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