2 The Q and P genes are linked and 20 map units apart In the

2. The Q and P genes are linked and 20 map units apart. In the cross Qp/qP x qp/qp what

fraction of the progeny will be QP/qp?

A) 5%

B) 10%

C) 25%

D) 40%

the answer is B but can someone please explain why?

Solution

The cross: Qp/qP x qp/qp (q and p -repulsion) means that the parental type gametes (Qp and qP) have the higher numbers (m) and the recombinant types (QP and qp) have the smaller numbers (n).
1% RF = 1 map unit; % RF = total number of recombinants/total progeny.
Q and P genes are linked and 20 map units apart,( the distance of 20 mu = 20% of recombinant frequency) the female parent (Qp/qP) will produce gametes:
Qp = 40%
qP = 40%
QP = 10%
qp = 10%

when crossing with male gamete ( i.e 100% qp) the progeny will be
Qp/qp = 40%
qP/qp = 40%
QP/qp = 10%
qp/qp = 10%

Therefore answer is B