5. The dry type of ear cerumen ("wax") is due to...

5. The dry type of ear cerumen ("wax") is due to homozygosity for a simple Mendelian recessive. Among American Indians the frequency of dry-cerumen individual is 60 percent. What is the frequency of the recessive allele? Assume Hardy-Weinberg equilibrium. 6. The allele for wet cerumen is the dominant allele and this trait is expressed in both homozygous dominant and heterozygotes. Among individuals with the wet type of cerumen, what is the frequency of heterozygotes and homozygotes?

Transcript

0:00 Into this question.

00:01 So let's call the recessive allele for the dry earwax little d.

00:14 So little d is going to indicate dry wax and then big d will indicate the wet wax.

00:28 Okay? and our given says that the frequency of the dry earwax, the homozygous recessive frequency, so little d little d, right? that is found in 60 % of individuals.

00:55 So little d little d, we can also represent 60 % as 0 .60.

01:05 It's a frequency.

01:08 And little d little d, the homozygous recessive, can also be represented as equal to q squared, right? the homozygous recessive, right? so it's a frequency of that.

01:23 And since that is a simple mendelian trait, we can just say that the frequency of this recessive little d allele, so this, the frequency of this, okay? the frequency of little d, we can just say that is equal to just q, right? and the frequency of the dominant allele can be represented.

01:49 We're going to say frequency of big d can be represented as just...

01:55 So we have an equation for this to solve for it and that is a hardy -weinberg equation to determine the frequencies of these.

02:06 So this is the equation p squared plus 2pq plus q squared is equal to 1, right? so since we know that q squared represents the frequency of the homozygous recessive and that p squared represents the frequency of the homozygous dominant individuals, the wet ear, we can solve for these different components, right? and we want the frequency of the heterozygous and homozygous individuals among the wet serum individuals.

02:44 So we can rearrange the equation for what we need.

02:49 So let's see.

02:58 So what we can do here is we can solve for q.

03:01 So we can take the square root of q squared, right? taking the square root of 0 .60 and so that will give us q, right? so q is going to now be equal to 0 .77 or also can be represented as 77%.

03:29 So if q is equal to 77%, if that's the frequency of that allele, then we can find the frequency of the p allele by taking 77 % and subtracting it from 100%.

03:50 Okay? so when we do that, then we have 23%.

03:56 So the frequency of the q is 77%, the frequency of the p or dominant allele is 23%.

04:06 Okay, so we're almost there because we have the frequency of q squared or the recessive.

04:18 We have the frequency of each of these single alleles here.

04:27 Now we need to find the frequency of the homozygous dominant.

04:33 So what we're just going to do is take this percent and we're going to solve for p squared...

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