Question

Two linked genes a and b show 30%recombination.The individual of a dihybrid cross ++/++ ab/ab shall produce gametes as:

1. ++80 : ab 20

2. ++40 : ab 40 : a10 : b 10

3. ++35 : ab 35 : a15 : +b15

4.++50: ab

Ans is (3)

Can I get the solution how to approach this questions

Answer 1

As it is mentioned a and b shows 30% recombination, this suggests there will be 30% of crossing over and thus the progeny will be a recombination of both the parents (means +a or +b). So half chances for each, thus from 30%, the 15% for +a and 15% for +b recombinants.

The percentage of linkage is 70% (100% - 30%) (Means chance for ++ or ab). So for both parents, there will be 35% and 35% chance of getting the progeny identical to the two parents.

So will get : ++35 : ab 35 : +a15 : +b15
So Answer is option:(3)
Read carefully for better understanding.