Question

Two genes are 22 map units apart on the same chromosome. A true-breeding GGhh individual is crossed to a true-breeding ggHH individual. The F1 offspring are mated to gghh individuals. If this testcross produces 1000 offspring, how many of them would you expect to be GgHh?

Select one:
a. 390
b. 250
c. 220
d. 110

Answer 1

d. 110

Step-by-step explanation:

Parental cross: Gh/Gh x gH/gH

F1: Gh/gH

The following test cross experiment is done:

Gh/gH x gh/gh

Gametes produced by these individuals:

- gh/gh: gh (probability of 1)

- Gh/gH:

• Gh (parental)
• gH (parental)
• GH (recombinant)
• gh (recombinant)

The formula that relates genetic distance with recombination frequency is:

Genetic Distance (m.u.)= Recombination Frequency X 100

In this problem:

22 m.u. / 100 = Recombination Frequency

0.22 = Recombination Frequency

The recombination frequency altogether is 0.22, but there are 2 possible types of recombinant gametes and when one is generated, the other one is generated as well. Therefore, each recombinant gamete has a frequency of half the total recombination frequency: 0.11

In an offspring of 1000 individuals, I would expect 110 to be GH/gh.