Question

If the a and b loci are 20 cM apart and an AA BB individual and an aa bb individual mate: What gametes will the F1 individuals produce, and in what proportions? What phenotypic classes in what proportions are expected in the F2 generation (assuming complete dominance for both genes) (show procedure, NO score for direct result)?

Answer 1

Mating of AABB X aabb

F1 generation AaBb

gamete of AaBb -----------------> AB, ab , Ab and aB

A total number of gametes is four, from which Ab and ab are non-recombinant, while Ab, an aB are recombinant.
The distance between these two loci is 20 cM, which tells us that there is a 20percent probability for these genes to be inherited together. We can conclude that the rest 80 percent would be non-recombinant heritage pattern.
Since the probability is the same for all the gametes, the percentage is 40 % for AB and 40 %for ab and 10% for Ab as well as 10% for aB of the non-recombinant alleles.

PROPORTION OF F2 generation

GAMETES	AB (40%)	ab (40%)	Ab (10%)	aB (10%)
AB(40%)	AABB 16%	AaBb  16%	AABb   4%	AaBB   4%
ab(40%)	AaBb 16%	aabb   16%	Aabb  4%	aaBb   4%
Ab (10%)	AABb 4%	Aabb   4%	AAbb 1%	AaBb  1%
aB (10%)	AaBB   4%	aaBb   4%	AaBb 1%	aaBB  1%

  Summary of phenotypes:

A and B 66%

A and b 9%

a and B 9%

a and b 16%