# Hardy-Weinberg Equilibrium Question

I have four questions concerning H-W Equilibrium:

(i) In a population of mice, the presence of black spots is the result of a homozygous recessive condition. If the frequency of the allele for this condition is 0.15, what is the approximate percentage of heterozygous genotypes in this mouse population? (Assume that the population is in Hardy-Weinberg equilibrium.)

I thought this implies that $q=.15$, $p=.85$ and thus the percentage of heterozygous genotypes is $2pq = .255$. Online answers seem to yield a ubiquitous $.72$.

(ii) In a population of giraffes, dark brown spots are the result of a homozygous recessive condition. If the frequency of the allele for this condition is 0.10, what percentage of the individuals in the next generation would be expected to be homozygous dominant?

Is this simply $(1-q)^2 = .81$?

(iii) In a population of monkeys, the allele that causes long hair at the tip of the tail (H) is dominant, while the allele that causes short hair at the tip of the tail (h) is recessive. If 67% of the monkeys have long hair at the tip of their tails, what is the frequency of the dominant allele?

I worked this as $p^2 + 2pq = .67$, so $q^2 = .33$, so $p = 1-\sqrt{q} = .4255$. Again, this seems to come up on the internet as incorrect.

Moreover, in the below picture: It seems to me that the answer should be $(1-G)^2 = (1-.45)^2$, but this does not appear as an answer.

Any help appreciated.

In a population of mice, the presence of black spots is the result of a homozygous recessive condition. If the frequency of the allele for this condition is 0.15, what is the approximate percentage of heterozygous genotypes in this mouse population? (Assume that the population is in Hardy-Weinberg equilibrium.)

We know the frequency of the allele (0.15) and we're looking for the frequency of the heterozygotes. $2\cdot 0.15(1-0.15) = 0.255$.

(ii) In a population of giraffes, dark brown spots are the result of a homozygous recessive condition. If the frequency of the allele for this condition is 0.10, what percentage of the individuals in the next generation would be expected to be homozygous dominant?

Yes, you are right it is 0.81

(iii) In a population of monkeys, the allele that causes long hair at the tip of the tail (H) is dominant, while the allele that causes short hair at the tip of the tail (h) is recessive. If 67% of the monkeys have long hair at the tip of their tails, what is the frequency of the dominant allele?

Although the notation is wrong ($p=1-\sqrt{q}$), the result is correct.

[last question]

As both genotypes GG and Gg are grey, we know that $p^2 + 2pq ≈ 0.45$ (Rather looks 0.48 from the figure though), where $p$ is the frequency of the G allele. From that you can calculate $p$ and $q$ and therefore calculate the frequency of the double homozygous gg

• For the first one, .385 was not an answer choice. – Anthony Peter Aug 31 '15 at 4:51
• Ha ha I somehow misread the question. Sorry about that, it is fixed now. – Remi.b Aug 31 '15 at 5:01