Question

In Drosophila, genes a and b control body size and color, respectively. Large body (a+) is dominant over miniature (a), and gray body (b+) is dominant over ebony (b). The two genes are located at positions 32.0 and 40.0 on a particular autosome. Note that crossing-over does not occur in males. A miniature female that is homozygous for b+ was mated with an ebony male that is homozygous for a . All the offspring were phenotypically wild-type (large body and gray).

a. What types of gametes will be produced by the Fı females, and in what percentages?
b. What types of offspring would you expect in the F2 generation, and in what percentages?

Answer 1

1

Female gametes:

ab= 0%

ab+=0%

a+b=0%

a+b+=0%

for the miniature phenotype to occur, it is necessary to contain two recessive characters and the female must have both for it to occur, if it is homozygous for b + it will have 2 alleles b +, understanding that the female is aab + b it will only occur gametes ab +

.

2. Phenotype

Miniature body + gray=25%

Large body +gray = 50%

Large body +ebony = 25%

Miniature body +ebony =0%

As the crossing cannot occur in males, the gametes it can produce are: ab + and a + b. Although the crossing can occur in women. The gametes produced are: ab +, a + b, ab and a + b +.

the crossing occurs only in the females generating the gametes ab +, a + b, ab and a + b +

The genotypes corresponding to:

Punnet graphic

large gray body: a + ab + b, a + ab + b +, a + a + b + b

big body and ebony: a + a + bb, a + abb

miniature and gray body: aab + b +, aab + b