Assume that gene a and b are linked and show40% recombination. If ++ / ++ individual iscrossed with ab / ab, then types and proportionsof gametes in F1 will be :-(1) ++ 20% : ab 20% : +b 20% : a + 40%(2) ++ 50% : ab 50%(3) ++ 25% : ab 25% : + b 25% : a + 25%(4) ++ 30% : ab 30% : + b 20% : a + 20%
The correct answer is 4) ++ 30% : ab 30% : + b 20% : a + 20%
As it is mentioned that due to incomplete linkage of genes a and b , the 40% recombinants are produced through crossing over between segments of genes of a and b. So the gametes of parental types ++ and ab should be produced in total frequency of 60% and the total frquencies of recombinants such as +b , b+ . +a or a+ should be 40%,. This is found in the option 4.
As it is mentioned that due to incomplete linkage of genes a and b , the 40% recombinants are produced through crossing over between segments of genes of a and b. So the gametes of parental types ++ and ab should be produced in total frequency of 60% and the total frquencies of recombinants such as +b , b+ . +a or a+ should be 40%,. This is found in the option 4.