Bio destroyer #255

[gn4]

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The question asks: If 36% of a population has blue eyes, what is the percentage of the recessive allele?

a) 60%
b) 64%
c) 36%
d) 50%
e) 0%

The answer is a, because 36%= q^2, then q=0.6

But I thought to get to the answer, we would have to count the people who are homozygous recessive(q^2) plus the people who are heterozygous(2pq) in order to find out the total percentage of the recessive allele in the population. Please tell me why my reasoning is off. I don't understand.

 

[virajpatel]

When it talks about the allele, you only look for the p or the q value.

 

[gn4]

let's say q represents blue eyes, to find the total, I only look at the people with blue eyes? I wouldn't need to look at the people with brown eyes who also may have the blue allele?

 

[mcdanielcars]

I had the same problem on a different test and couldn't figure it out. In the end I just decided that maybe that number was so small that it was insignificant? But I thought the same thing as you. Just be aware that on the real DAT, everything is straight forward. If you're like me, you have a tendency to think too much and look way past what they're actually trying to test you on... which is bad. haha.🙂

 

[haiKUHN]

They tell you that 36% of the population phenotypically display the recessive trait. To take that down to allelic frequency, you take the square root of 0.36. You don't need to consider the heterozygous fact, 2pq, because they're simply asking you for the allelic percent. The 2pq value tells you what percent of the population displays the dominant trait, even if they're heterozygous. Basically, you'd be using the percent you find (0.6) to figure out how that plays into the amount of individuals who phenotypically display that trait in a population.

Try to think of the "p+q=1" equation in reference to genotypes/allelic frequency, and

"p^2 + 2pq + p^2 = 1" in reference to phenotypic percentages of a population.

 

[gn4]

They tell you that 36% of the population phenotypically display the recessive trait. To take that down to allelic frequency, you take the square root of 0.36. You don't need to consider the heterozygous fact, 2pq, because they're simply asking you for the allelic percent. The 2pq value tells you what percent of the population displays the dominant trait, even if they're heterozygous. Basically, you'd be using the percent you find (0.6) to figure out how that plays into the amount of individuals who phenotypically display that trait in a population.

Try to think of the "p+q=1" equation in reference to genotypes/allelic frequency, and

"p^2 + 2pq + p^2 = 1" in reference to phenotypic percentages of a population.

oh okay. wow. thanks for a great explanation. Appreciate it.

 

[gn4]

I had the same problem on a different test and couldn't figure it out. In the end I just decided that maybe that number was so small that it was insignificant? But I thought the same thing as you. Just be aware that on the real DAT, everything is straight forward. If you're like me, you have a tendency to think too much and look way past what they're actually trying to test you on... which is bad. haha.🙂

haha. yea. most of these questions, I tend to overthink on. I did a practice test the other day and found out that, had I gone with my first instinct answer, I would have scored a lot higher on the sciences. I kept changing my answer. It seems that I should just think it's straightforward. No trying to trick me.