Question

You are mapping the location of two genes in Drosophila, listless land blind b, which are located on the same chromosome. (I* I* b*b) and (I* l b*b) flies are normal, but (l I b b) flies don't move around very much and cannot detect the location of a light source. In your parental generation you mate a true breeding wild-type female with a listless blind male. Then you use the resulting F₁ females to perform a test-cross and get the following F₂ results: listless, sighted: 100 listless, blind: 400 normal activity, sighted 400 normal activity, blind 100 Because your F₁ female flies can see, all of the blind F₂ offspring must have resulted from recombination events.

O True
O False

Answer 1

The question discusses mapping genes in Drosophila using a test-cross and makes an incorrect assumption about blind offspring resulting exclusively from recombination events, which is false. Recombinant offspring are not the only source of inherited traits, as parental genotypes carrying recessive alleles can also contribute to offspring phenotype.

Step-by-step explanation:

The student's question is concerned with mapping the location of two genes, listless (l) and blind (b), on the same chromosome of Drosophila melanogaster using a test-cross. This involves breeding an F1 generation and then crossing those offspring with known genotypes to determine recombination frequencies and gene mapping. Specifically, these genes are not associated with the X chromosome but are instead autosomal. If all blind F2 offspring result solely from recombination events during the test cross, this would indicate that neither the listless nor the blind traits are tightly linked and there is a recombination between the genes. However, the question seems to suggest an incorrect understanding of the genetics involved.

The false statement here could be attributed to assuming that all blind offspring must have resulted from recombination events, which is not necessarily true. Recombination generally equates to genetic diversity, but not all genetically diverse traits must have arisen from recombination. Some could be due to the parental genotypes carrying the recessive alleles. Moreover, if the listless and blind traits were perfectly linked (no recombination), you would expect equal numbers of listless blind and normal sighted offspring, not the observed numbers.

Answer 2

The claim that all blind F2 offspring from a genetic cross in Drosophila result from recombination events is false, as the frequency of phenotypes indicates that blindness is linked to another trait.

Step-by-step explanation:

The question revolves around the genetic mapping of two genes in Drosophila (fruit flies) and whether all blind F2 offspring are the result of recombination events. According to the F2 results presented, the statement that all of the blind F2 offspring must have resulted from recombination events is False.

The numbers indicate that the most common phenotypes in the F2 generation are listless, blind and normal activity, sighted, suggesting that these traits are linked and non-recombinant.

The phenotypes listless, sighted and normal activity, blind occur less frequently, indicating that they are the result of recombinant events. When mapping genes, it's crucial to consider the linkage between them, as linked genes do not assort independently and are inherited together more frequently than by chance.