In Drosophila,the allele red eyes (bw+)is dominant to the allele for brown eyes (bw).At another gene locus on the same chromosome,the allele for thin wing veins (hv+)is dominant to the allele for heavy wing veins (hv).Flies homozygous for bw and hv+ are crossed to flies homozygous for bw+ and hv to obtain doubly heterozygous F 1 progeny. -Given that these two gene loci are very closely linked,the phenotypic ratio in the F₂ generation should be closest to A)1 brown eye,heavy wing veins: 2 red eye,thin wing veins: 1 brown eye,thin wing veins B)1 brown eye,thin wing veins: 2 red eye,thin wing veins: 1 red eye,heavy wing veins C)3 red eye,thin wing veins: 1 brown eye,heavy wing veins D)1 brown eye: 1 red eye: 1 heavy wing veins: 1 thin wing veins

Question

Quizplus · Accepted Answer

The two gene loci are very closely linked, meaning that they are likely to assort together and not undergo independent assortment. From the initial cross, we know that one parent is homozygous for bw and hv+ while the other parent is homozygous for bw+ and hv. This means that the F1 generation will all be heterozygous for both genes, with the genotype bw+ bw hv+ hv.

When these F1 individuals undergo meiosis, the two gene loci will assort together as a unit. This means that the gametes produced will be either bw+ hv+ or bw hv. There are two possible gamete types for each parent, so there are four possible gamete combinations in the offspring: bw+ hv+, bw hv, bw+ hv, and bw hv+.

To determine the phenotypic ratios in the offspring, we need to consider the dominant and recessive alleles at each gene locus. At the bw/bw+ locus, red eyes (bw+) are dominant over brown eyes (bw). At the hv/hv+ locus, thin wings (hv+) are dominant over heavy wings (hv).

Using a Punnett square, we can determine the possible genotypes and phenotypes of the offspring:

|      | bw+ hv+ | bw hv   | bw+ hv  | bw hv+  |
|------|--------|--------|--------|--------|
| bw+ hv+ | bw+ bw+ hv+ hv+ | bw+ bw hv+ hv | bw+ bw+ hv hv+ | bw+ bw hv hv   |
| bw hv   | bw+ bw hv+ hv | bw bw hv hv | bw+ bw hv+ hv | bw bw hv+ hv   |
| bw+ hv  | bw+ bw+ hv hv+ | bw+ bw hv hv | bw+ bw+ hv+ hv | bw+ bw hv+ hv |
| bw hv+  | bw+ bw hv hv+ | bw bw hv+ hv | bw+ bw hv hv+ | bw bw hv hv+ |

From this Punnett square, we can see that there are three possible phenotypes in the offspring:

- 1 brown eye, thin wing veins (bw hv or bw bw hv+)
- 2 red eyes, thin wing veins (bw+ bw+ hv hv+ or bw+ bw hv hv or bw+ bw+ hv hv)
- 1 red eye, heavy wing veins (bw+ bw hv+ hv)

The closest phenotypic ratio listed is B) 1 brown eye, thin wing veins: 2 red eye, thin wing veins: 1 red eye, heavy wing veins, which matches the three possible phenotypes we just determined. Therefore, the best choice is B.

In Drosophila,the Allele Red Eyes (Bw+)is Dominant to the Allele