In Drosophila, recessive mutations in the fruitless gene (fru) re...

Question

In Drosophila, recessive mutations in the fruitless gene (fru) result in males courting other males; and recessive mutations in the Antennapedia gene (Ant⁻) lead to defects in the body plan, specifically in the thoracic region of the body, where mutants fail to develop legs. The two genes map 15 cM apart on chromosome 3. You have isolated a new dominant Antdᵈ mutant allele that you induced by treating your flies with X-rays. Your new mutant has legs developing instead of antennae on the head of the fly. You cross your newly induced dominant Antᵈ mutant (a pure-breeding line) with a homozygous recessive fru mutant (which is homozygous wild type at the Ant⁺ locus), as diagrammed below:

Your cross results in the following phenotypic proportions:

Legs on head, normal courting behavior 75
Normal head, abnormal courting behavior 25
Legs on head, abnormal courting behavior 0
Normal head, normal courting behavior 0

Provide a genetic explanation for these results and describe a test for your hypothesis

Accepted Answer

Hello, everyone. Let's look at our next question. It says which of the following can result from a homeo gene mutation. Andrea choice, a absence of the anterior structures, choice B, loss of contiguous body segments. Choice C displaced body parts or choice D all of the above. When we talk about the hoo genes, we're talking about the genes that direct the development of specific anatomical structures. So they kick in after we've had the segmentation of our embryo and then the perro genes have come in and we have our embryo divided into 14 segments with polarity established. So since they direct the development of those anatomical structures like legs and antenna and wings, a mutation in one of those genes will result in choice B or excuse me, choice C displaced body parts in choice A, it says absence of the anterior structures. If you're missing everything in the interior of the dys Sophal, you're talking about a mutation in the gene that establishes that whole an interior region. That's one of the maternal effects genes, uh specifically the bio gene. So that would be a mutation to the bi coid gene if you've lost all of the interior structures. Uh because again, the hoo genes develop specific anatomical structures, not this whole an interior region. So that's why choice A isn't correct choice B loss of contiguous body segments, this would be loss of a whole group, a contiguous or neighboring. So neighboring body segments. And so when we think about what controls the development of a group of neighboring body segments, we're going to talk about a mutation to one of the gap genes. And indeed, that's why they're called gap genes because the mutation in those genes results in a gap in the development of the embryo since you've got a whole uh group of segments that are missing. So that's why choice B isn't our correct answer. And then choice D all the above obviously is not correct since we have only one correct answer here. So again, what results from a mutation in one of the homeo genes and Sophal choice C displaced body parts? See you in the next video.

Key Concepts

Gene Interaction and Epistasis

Dominance and Recessiveness

Phenotypic Ratios and Genetic Crosses

Watch next