Question

During a dihybrid cross involving two linked genes (two-point testcross), 20 flies showed recombinant phenotypes, whereas 480 flies showed the parental phenotypes. How far apart are these linked genes from each other?

a. 20 cM
b. 7.5 cM
c. 4 cM
d. 0.04 cM
e. 8 cM

Answer 1

The two linked genes in this dihybrid cross are 4 cm apart.

Step-by-step explanation:

Geneticists have used the proportion of recombinant gametes (the ones not like the parents) as a measure of how far apart genes are on a chromosome. In a dihybrid cross involving two linked genes, 20 flies showed recombinant phenotypes, while 480 flies showed parental phenotypes. This means that 20 out of 500 flies displayed a nonparental combination of traits. To calculate the recombination frequency, we divide the number of recombinant flies by the total number of flies: 20/500 = 0.04. This recombination frequency corresponds to a genetic distance of 4 cm(centimorgans) between the two linked genes.