Ss 20 sf 12 and ff 18 what are the allele frequencies of s...

SS = 20, SF = 12, and FF = 18. What are the allele frequencies of S and F in this population? What are the allele frequencies of S and F in this population? Based on those allele frequencies, what are the expected genotype frequencies, if this population was in HW equilibrium? Is the number of heterozygotes greater or less than what we would expect for HW equilibrium?

Transcript

00:01 So i'm going to go through this a little bit quickly, just because there's a lot to cover here.

00:04 Let's start by writing down the frequency of our genotypes.

00:08 So we have fast, fast, fast, slow, and then slow, slow.

00:14 And ultimately, the question we're being asked is the number of individuals in these three different genotypes in hardy -weinberg equilibrium.

00:25 Note that the number of individuals in the population conveniently adds up to 100.

00:31 The first big step that we have to do is calculate the proportion of alleles in this population that are f and the proportion that are s.

00:41 So to get the proportion that are f, you start by basically counting.

00:48 So we have 32 individuals that are homozygous for f, so that we say 32 times.

00:56 Two because each of them has two f big f alleles.

01:00 And then we say we also have 46 individuals who have just one f and if you add that up that means we have a hundred and ten big f alleles in the population.

01:15 Remember that there are 200 individuals but that means that there's 200 alleles in the population.

01:26 So a hundred and ten of the total number of alleles in the population is big f.

01:32 And so 110 out of 200 or f.

01:36 And that gives us our frequency, which is 0 .55.

01:49 And we can do the same thing for s.

01:51 So the number of s, i forgot to write my f there, is going to be figured out the same way.

01:58 46 of the individuals have one s allele.

02:02 22 individuals have two copies of the s allele.

02:08 That works out to be 90 individuals, so 90 us out of 200 alleles in the population, and so that's 0 .45.

02:22 So we'll make this value p, the frequency of the big f is 0 .55, which is p, and we'll make 0 .45, and we'll make 0 .45, 4 or 5 q.

02:35 All right.

02:36 So again, we're trying to figure out if this population is in hardy -weinberg equilibrium.

02:41 We now know the frequency of p of the f and s allele.

02:44 We have our p's and q's.

02:46 If the population is in hardy -wineberg equilibrium, then we should be able to use the hardy -winberg formula.

02:53 And so what you do is you calculate p squared plus 2pq plus q squared.

03:02 And that should give us the expected number of individuals that have these different genotypes.

03:12 So, p squared is 0 .55 squared...

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