Five percent of quarter horses in the United States are heterozygous for the recessive lethal allele that causes glycogen branching enzyme deficiency (GBED). Assuming that quarter horses are randomly mated, this means that the frequency of this allele is q = 0.025. If the GBED allele is maintained in the population by mutation-selection balance, what is the mutation rate to the disease allele? (Recall that the equilibrium frequency for a recessive allele under mutation-selection balance is q = $\nu$ $\mu$/s, where $\mu$ is the rate of mutation to the disease allele and s is the selection coefficient against that allele. In the case of a lethal allele, s =1.)

Question

Quizplus · Accepted Answer

The equilibrium frequency for a recessive allele under mutation-selection balance is given by $q = \sqrt{\mu/s}$, where $\mu$ is the mutation rate and $s$ is the selection coefficient. For a lethal allele, $s = 1$, so the equation simplifies to $q = \sqrt{\mu}$. Given that $q = 0.025$, we solve for $\mu$ by squaring both sides: $\mu = q^2 = (0.025)^2 = 0.000625$.

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