Question

in humans, ear wax might be controlled by a single gene showing mendelian inheritance, where the two phenotypes are wet ear wax and dry ear wax, and the wet ear wax trait is dominant to the dry ear wax trait. interested in understanding this trait, you study families and compile the following data. what about this data suggests that ear wax is a mendelian trait governed by a single gene? there are fewer offspring with dominant alleles than with recessive alleles. there are two phenotypes and three genotypes. the data do not suggest that ear wax is governed by a single trait. since no pairs of parents with dry ear wax produced an offspring with wet earwax, this trait is likely to be governed by a single gene.

Explanation:

• Mendelian traits follow specific inheritance patterns. A single - gene trait with a dominant - recessive relationship would show that parents with a recessive phenotype (dry ear wax in this case) cannot produce offspring with the dominant phenotype (wet ear wax) if it is a single - gene trait. Here, parents with dry ear wax (homozygous recessive, assuming the gene for ear wax type is \(W\) for wet (dominant) and \(w\) for dry (recessive), so their genotype is \(ww\)) produce only dry - ear - wax offspring.
• For parents with wet ear wax, if they are heterozygous (\(Ww\)), a cross \(Ww\times Ww\) would give a phenotypic ratio close to \(3:1\) (wet:dry). The ratio of wet to dry offspring for parents with wet ear wax is \(35:12\approx 3:1\).
• For the cross of one wet - ear - wax (assume \(Ww\)) and one dry - ear - wax (\(ww\)) parent, the expected ratio of wet (\(Ww\)) to dry (\(ww\)) offspring is \(1:1\), and the observed ratio \(205:195\approx1:1\)

Answer:

Since no pairs of parents with dry ear wax produced an offspring with wet earwax, this trait is likely to be governed by a single gene.