Answer to Question #316932 in Genetics for Nhlonipho Manganyi

Question

A researcher has two pure breeding strains of fruit flies: strain A and strain B.

Strain A produces only enzyme A and strain B only enzyme B. The alleles

coding for enzyme A and enzyme B are the only alleles involved here and occur at the

same locus. The researcher crossed a fly from strain A with one from strain B and found

that all the offspring (F1 generation) could produce both enzyme A and enzyme B. When he

crossed two of the F1 generation flies, he found the following in the offspring:

658 produced enzyme A, 1364 produced enzyme A and B, 581 produced enzyme B

What type of inheritance can produce these results? Using appropriate symbols, show the

researcher’s cross (up to the F2 generation) What would the expected result be if one of the

offspring that can produce both enzyme A and enzyme B were crossed with one that can only

produce enzyme A (include a Punnett Square)?

10 Marks

Answer 1

There is single dihybrid inheritance. The type of dominance of the alleles A and B is complete.

The cross:

P: AAbb (♀) + aaBB (♂)

↓

F1: AaBb (♀) + AaBb (♂) + AaBb + AaBb

↓

F2: AABB + AABb + AABb + AAbb + AaBB + AaBb + AaBb (♀) + Aabb (♂) + AaBB + AaBb + AaBb + Aabb + aaBB + aaBb + aaBb + aabb

↓

F3: