In Drosophila, the X-linked recessive mutation vermilion (v) causes bright red eyes, in contrast to the brick-red eyes of wild type. A separate autosomal recessive mutation, suppressor of vermilion (su-v), causes flies homozygous or hemizygous for v to have wild-type eyes. In the absence of vermilion alleles, su-v has no effect on eye color. Determine the F₁ and F₂ phenotypic ratios from a cross between a female with wild-type alleles at the vermilion locus, but who is homozygous for su-v, with a vermilion male who has wild-type alleles at the su-v locus.

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Hi everyone welcome back. Here's our next problem. It says joseph Emma's white eye Is a sex linked recessive trait. What characteristics are present in the F- one generation of a cross between a male with dominant red eyes and a white eyed female. So let's think about what the genotype sar the parents that were crossing the male if he has red eyes well he only has one X. Chromosome. So that will be X. Subscript R. Why is his genotype? But the white eyed female since she shows the recessive trait and has two X chromosomes, her genotype would be X. W. X. W. So let's think about what the outcome would be of this cross in the F one generation micro little punnett square here. So we've got our mail up here. X. Ry are female over here X. W. X. W. And let's look at the outcome of our offspring. So we see we got two females X. W. X. R. And as for the males they can only inherit next chromosome from their mother. And yes if a female shows a recessive excellent trait all of her sons will show that trait because she can only pass on that recessive trait with the X. And these sons only inherit a single X from their mother. So the result of this will have all of the females will be hetero sickness and therefore show the dominant trait. So the females will have red eyes. But the males with their single X chromosome inherited from their mother showing the recessive trait. We'll all have white eyes. So let's go look over at our answer choices and we see that choice C. Is indeed. All the females were red eyed and all the males white eyed. We can see our other answer choices are incorrect. Choice A. Says all females and all males were white eyed. But again the females inherit the red alil from their father and since that's dominant they show the dominant trait choice B. 50% of males and 50% of females white eyed. Um Well again the females are heterocyclic so they show the dominant red eyed trait. The males only have a single X. Inherited from the mother who has two recessive values so they will all have the recessive trait. So that's not our answer. And finally Choice D all females and all males were red eyed. But again the males can only inherit a wide eyed gene um from their mother since they do not inherit an X. From their father. So choice is also incorrect. The outcome of this cross of red eyed male with white eyed female and the F one generation is choice. See all females were red eyed and all males white. I'd see you in the next video

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Key Concepts

X-linked Recessive Inheritance

Autosomal Recessive Suppressor Mutation

Genetic Crosses and Phenotypic Ratios