Question

In a population of tree frogs, the allele that causes yellow eyes (Y) is dominant over the allele that causes orange eyes (y). If 85% of the frogs have yellow eyes, what is the frequency of the dominant allele?

Answer 1

I'll assume you know the Hardy-Weinberg Principle:
p is the frequency of Y in the population; q is the frequency of y in the population.

p + q = 1 (1)

p^2 tells us the frequency of homozygous dominants
q^2 tells us the frequency of homozygous recessives
2pq tells us the frequency of heterozygotes

Since 85% of the frogs have yellow eyes, we can make the following expression:

p^2 + 2pq = 0.85 (2)

Now its just a question of solving (1) and (2) simultaneously, which I think involves a quadratic... In any case hope this helps!

Answer 2

Just realised I seriously over complicated how you work this out!

If 85% have yellow eyes, then 15% must have orange eyes...and since only homozygous recessive (yy) have orange eyes, then p^2 = 0.15... so square root that and then use 1=p+q and your done, without having to solve a quadratic!

Sorry for the first reply!