A species of fly has two alleles for the length of their legs. The allele for long legs is dominant and is represented by p. The allele for short legs is recessive and is represented by q. The Hardy-Weinberg equation is shown below. If 33 of 100 organisms have short legs, what is p?

The answer is 0.43

To calculate p we will use one of two formulas of the Hardy-Weinberg principle:

p² + 2pq + q² = 1 and p + q = 1

where:

p - the frequency of the allele for long legs which is a dominant trait.

q - the frequency of the allele for short legs which is a recessive trait.

p² - the frequency of dominant homozygote (with long legs)

2pq - the frequency of heterozygote (with long legs)

q² - the frequency of recessive homozygote (with short legs)

So, 33 of 100 organisms have short legs. The frequency of recessive homozygote is represented by q²:

q² = 33/100 = 0.33

⇒ q = √0.33 = 0.57

Using the formula:

p + q = 1

p = 1 - q = 1 - 0.57 = 0.43

Therefore, p = 0.43