Question

Ability to roll the tongue is caused by a dominant allele. A woman is a "roller," but one of her parents is not. What is the woman's genotype?

Ability to roll the tongue is caused by a dominant allele. A woman is a "roller," but one of her parents is not. What is the woman's genotype?
a) homozygous dominant
b) heterozygous
c) homozygous recessive
d) cannot be determined from this information

Answer 1

The woman's genotype for the tongue-rolling trait is heterozygous (Rr), as she can roll her tongue which is a dominant trait, but one of her parents cannot roll, indicating she inherited a recessive allele from that parent.

Step-by-step explanation:

If a woman is able to roll her tongue (a dominant trait), but one of her parents cannot, this means that she has received a dominant allele from the parent who can roll their tongue and a recessive allele from the parent who cannot. She must therefore be heterozygous for the tongue-rolling trait, with her genotype being 'Rr' (where 'R' represents the dominant allele for tongue-rolling and 'r' represents the recessive allele).

Since tongue-rolling is a dominant trait, the woman's ability to exhibit this trait means she has at least one dominant allele. However, since she has a parent who cannot roll their tongue, that parent must have the genotype 'rr' (homozygous recessive), passing on a recessive allele to her. The only possibility for her to be a roller yet have a non-roller parent is if she has one dominant and one recessive allele, indicating a heterozygous genotype 'Rr'.

Accordingly, the correct answer to the question, 'What is the woman's genotype?' would be option b) heterozygous.