Question

You are studying a gene that controls ossicone (horn) length in giraffes. The wild-type long-ossicone allele (L) is dominant to the mutant short-ossicone (l) allele. However the L allele is only 60% penetrant. You cross two heterozygous giraffes. What proportion of offspring would you expect to exhibit the long ossicone phenotype? Assume the penetrance of L applies equally to both homozygotes and heterozygotes.

a) 0.36

b) 0.48

c) 0.60

d) 0.72

Answer 1

When two heterozygous giraffes are crossed, the proportion of offspring expected to exhibit the long ossicone phenotype would be 80%.

Step-by-step explanation:

To determine the proportion of offspring that would exhibit the long ossicone phenotype, we need to consider the dominance and penetrance of the alleles involved. In this case, the wild-type long-ossicone allele (L) is dominant to the mutant short-ossicone (l) allele, but the L allele is only 60% penetrant. When two heterozygous giraffes are crossed, there are three possible genotypes: LL, Ll, and ll. Since the L allele is dominant, both LL and Ll individuals would exhibit the long ossicone phenotype. Therefore, the proportion of offspring expected to exhibit the long ossicone phenotype would be the sum of the proportions of LL and Ll genotypes. Since the L allele is 60% penetrant, the proportion of individuals with the LL genotype that exhibit the long ossicone phenotype would be 100% (1), while the proportion of individuals with the Ll genotype that exhibit the long ossicone phenotype would be 60% (0.6). Therefore, the proportion of offspring expected to exhibit the long ossicone phenotype would be (1/2) + (1/2 * 0.6) = 0.8, or 80%.