In humans, albinism is caused by loss-of-function mutations in genes involved in the synthesis of melanin, the dark pigment in skin. Only people homozygous for a loss-of-function allele (genotype aa) have the albino phenotype. In Americans of northern European ancestry, albino individuals are present at a frequency of about 1 in 10,000 (or 0.0001). Assuming that genotypes are in Hardy–Weinberg equilibrium, what is the predicted frequency of Caucasians in the United States who carry a single allele for albinism?

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Accepted Answer

Welcome back. Let's look through our next problem. It says the flower color and a plant is coded by a single gene. And the alleles F. W. And F. Are for the same are co dominant. White flowers are homos. I guess for the L E L. F. W. Red flowers are homos I guess for the L E L. F. R. If both alleles are present together, the flowers will be pink. The white flowers are present at a frequency of one in 100. What is the predicted frequency of pink flowers? If gina types are in hardy Weinberg equilibrium. So a lot of stuff to sort through here. When we think about hardy Weinberg equilibrium, let's recall from our content video that we have two equations that go with that we usually think of it in terms of a dominant and recessive alleles but it will work with a co dominant allele. Again, co dominant means you don't have one masking the other in your phenotype. Rather when you haven't had, it expresses the phenotype in between the phenotype of the two alleles. So in hardy Weinberg. In our usual format, we'd say the frequency of valuable big A. We say that equals P. And the frequency of ali a little A. Is Q. Then we know that P plus Q. Must equal one because there's only two alleles of this gene. So in terms of the whole population, the frequency, you know everything has to be either one or the other. The frequencies of the appeal and I will acute must equal one. So that's the frequency of the aliens themselves. We have a second equation where we say that the frequency in this case homocide is dominant, I want to call that P squared. The frequency of the homicide is recessive, it's Q. Squared. And then the frequency of the head rose. I get it, It's two p. q. And then again because the offspring their genotype. So this is the frequency of the alleles appear. Then now I'm dealing with the frequency of the jena types. And again, because there's only three possible Jenna types. All these frequencies P squared plus Q squared plus two PQ must also equal one. So those are hardy Weinberg equations. Now we can easily adapt it to a co dominant situation because we have just two alleles. So in this case we have a frequency of F. W. That's the white a leo. And we have a frequency of our red alley but we don't actually know the frequency of the aliens yet. Because what we're given is the frequency of white flowers. So we're looking actually from what I give us our problem at the frequency of the Jenna types. So again, our white flowers, we know are homos, I guess for the white allele. So frequency of white flowers is going to be frequency of F. W. F. W. The homos. I guess for the white gene and we know that that's one in Which equals .01. Well that frequency we're gonna call it P squared. We're going to compare it to big a big A. So then the frequency of so then P. Here P squared is 0.1. P must equal 0.1. Well, going back to this guy over here, P plus Q equals one. We know that Q. Which will be the frequency oops frequency of the red Must equal 1 -0.1 equals 0.9. So now we have F. W. Which we know is P. 0.1 frequency of the red, a little 0.9. So now we have our P. And our Q. So with that in mind this is analogous to the situation. We want the frequency of the heterocyclic because our pink flower Is hetero cigarettes, one copy of each gene. So we know the frequency of the Hetero is two PQ. So therefore the frequency of our pink flower F. W. F. R has to equal to P. Q. Equal two times 0.1 times 0.9. And that will equal 0.18. That's going to be the frequency of the hetero zigging and therefore the frequency of the pink flower in the situation. So we look at our answer choices, we see that choice d. is indeed 0.18. So we have our correct answer. See you in the next video

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Key Concepts

Albinism and Melanin Synthesis

Hardy-Weinberg Equilibrium

Carrier Frequency Calculation