Question

A geneticist discovers a new mutation in Drosophila melanogaster that causes the flies to shake and quiver. She calls this mutation spastic (sps) and determines that it is due to an autosomal recessive gene. She wants to determine whether the gene encoding spastic is linked to the recessive gene for vestigial wings (vg). She crosses a fly homozygous for spastic and vestigial traits with a fly homozygous for the wild-type traits and then uses the resulting F1 females in a testcross. She obtains the following flies from this testcross.

vg⁺ sps⁺ 230
vg sps 224
vg sps⁺ 97
vg⁺ sps 99

Answer 1

The geneticist's work suggests that the genes for spastic behavior and vestigial wings in Drosophila melanogaster are linked. A testcross between F1 females and a homozygous wild-type fly shows a higher number of parental type offspring compared to recombinant types, indicating linkage.

Step-by-step explanation:

The subject of the question is Biology, specifically involving genetics in Drosophila melanogaster (fruit flies). In the student's scenario, we have a case where a geneticist is attempting to determine if two genes are linked. A recessive autosomal mutation causing flies to shake and quiver (sps) is being tested for linkage to the recessive gene for vestigial wings (vg). A testcross of F1 females with a fly homozygous for the wild-type traits produced the following offspring: vg+ sps+ (230), vg sps (224), vg sps+ (97), and vg+ sps (99). If the genes were unlinked, we would expect the offspring numbers to be equal for these four types due to independent assortment.

However, since the numbers for the parental types (vg+ sps+ and vg sps) are significantly higher than the recombinant types (vg sps+ and vg+ sps), this suggests that the genes for spastic and vestigial wings are linked and lie close to each other on the same chromosome. Recombination during gamete formation in the F1 females has resulted in fewer offspring with the recombinant phenotypes.

The final answer is that the spastic gene and the gene for vestigial wings are indeed linked.