Question

In the parental generation, a male fruit fly with a gray body (BB) and straight wings (CC) was crossed with a female fruit fly with a black body (bb) and curved wings (cc). The F1 flies all had gray bodies and straight wings. A female F1 fly was crossed with a male fly that was homozygous recessive for both traits. The female fly had the B and C alleles on one chromosome and the b and c alleles on the other chromosome. Because the genes are linked, the expected ratio in the F2 generation would be 50% with gray bodies and straight wings and 50% with black bodies and curved wings. But four different phenotype combinations appear in the offspring, with two expected, but there were also offspring with gray bodies and curved wings and offspring with black bodies and straight wings. Which of the following best explains what happened?

1. A recombination occurred during the formation of the F1 female's egg cells.
2. A mutation changed the genotype of a portion of the flies in the F2 generation.
3. A mutation changed the genotype of the F1 male's DNA.
4. A recombination occurred during the formation of the F1 male's sperm cells.
5. Independent assortment resulted in the new combination of traits in the F2 generation.

Answer 1

Step-by-step explanation:

1) A new combination has occurred while the female F1's ovule was forming.

since the female has heterozygosity (BC / bc) and in species such as Drosophila only the females have the capacity to produce recombinant germ cells, the male is not going to show recombination. a suitable independent distribution would generate the four phenotypes in a 1: 1: 1: 1 ratio (25% of each). however there may be little recombination or the link is not absolute.