While vermilion is X-linked in Drosophila and causes ...

Question

While vermilion is X-linked in Drosophila and causes the eye color to be bright red, brown is an autosomal recessive mutation that causes the eye to be brown. Flies carrying both mutations lose all pigmentation and are white-eyed. Predict the F₁ and F₂ results of the following crosses:
vermilion females x brown males

vermilion females x brown males

Accepted Answer

Welcome back. Let's look at our next question. It says the ratio of red and white eyed Drosophila. When a white eyed recessive male and red eyed dominant female is crossed in the F two generation is, and we have a choice of four different ratios. So we have two generations. So let's start with our original parents of the F. One generation. We have a white eyed male. Well let's recall from our content video that the eye color gene is X. Linked. So a white eyed male, it's going to have to call this X. Usually X. With the subscript either W. Or R. So this males white eyed. He has only one X. Chromosome. With a gene for white eyes. And then the Y. And we're gonna cross him with a red eyed female. Um We're not told she's headed this. And since this is our original generation, we're going to assume she's homesickness for the red eyed gene. So X. R. X. R. So we can go ahead and look at that pen it square. But remembering that our answer is asking about the F. two generation. So we don't want to forget that. So let's put up a little punnett square for that cross Remembering that we call this f. one. So here's our mail, X. W. Y. There's his gametes and the female gametes here, X. R. And X. Are so the offspring in the F. One generation here. And we have to remember that our question is going to ask us about phenotype, not genotype since it's asking about eye color. So the F one generation um are the female offspring will all be hetero zegas. So 100% of them. Hetero sickness. And therefore with red eyes, the males of the among the offspring will all have red eyes. And of course they only have one um X. Chromosome. So they only have the one gene for red eyes. Now let's go on to our f. two generation looking at this cross. So we'll put up another pundit square right here. So let's put our males from the F. One generation which are X. R. Y. And then our hair grow six females from from that F one generation here X. R. X. W. And now we look at this offspring In the F two generation. So we fill in the square and we see that we have all the females will show red eyes. They're not Jenna typically all the same half the females are homesickness for the red eye gene. Half of them are head shots. But since that red eye gene is dominant, they will all have red eyes. Of the males. Half of them have a red eye gene and half of them have a white eyed gene. So they will be half red eyed and half white eyed. So the end result is we have a ratio of 3-1 red eyed, two white eyed In the F two generation. So let's look over here And that we have answer choice c. 3-1. So what the ratio of red and white eyed Drosophila when a white eyed male and red eyed female is crossed in the F. Two generation is choice C. 3 to 1. See you in the next video.

Key Concepts

X-linked Inheritance

Autosomal Recessive Inheritance

Epistasis and Interaction of Multiple Genes

Watch next