A leucine-requiring mutant strain of haploid yeast is crossed to a cysteine-requiring mutant strain.Assuming independent assortment,what proportion of the spores produced will be mutant?

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In this scenario, each parent contributes one mutant allele, but for different genes. Assuming independent assortment, the probability that a spore will inherit both mutant alleles (and thus be a mutant) is the sum of the probabilities of inheriting either mutant allele individually, minus the probability of inheriting both (to avoid double counting). Since each allele has a 1/2 chance of being passed on (for each of the two genes), the calculation for getting at least one mutant allele is 1 - the probability of getting neither mutant allele, which is 1 - (1/2 * 1/2) = 1 - 1/4 = 3/4.

A Leucine-Requiring Mutant Strain of Haploid Yeast Is Crossed to a Cysteine-Requiring