Question

A and B genes are linked. What shall be genotype of progeny in a cross between AB/ab and ab/ab?

• A. AAbb and aabb
• B. AaBb and aabb
• C. AABB and aabb
• D. None of the above

Answer 1

Answer: (B)

AaBb and aabb

Since A and B genes are linked, the parental genotypes "AB/ab" and "ab/ab" will produce only non-cross over gametes. Recombinant gametes are not produced here; the genotype AAbb is product of fusion of recombinant gametes (Ab x Ab) which makes option A wrong. Since the second parent does not have "AB" gamete, AABB genotype cant be obtained from a cross between AB/ab and ab/ab. Thus, option C is wrong.
Parent generation "AB/ab" x "ab/ab"

Gametes : AB/ab --> ab/ab	AB	ab
ab	AaBb	aabb
ab	AaBb	aabb

Offspring genotypic ratio = 1 AaBb: 1 aabb. Hence, option B is correct.