Final answer:
The woman's genotype is heterozygous (Aa) for the ability to roll the tongue, as she received a dominant allele from one parent and a recessive allele from the other.
Step-by-step explanation:
The ability to roll the tongue is caused by a dominant allele. If a woman can roll her tongue (roller), but one of her parents cannot, this means that she must have received the dominant allele from the parent who can roll the tongue and the recessive allele from the parent who cannot. As she is expressing the trait, she must have at least one dominant allele. Since we know she has one parent who cannot roll the tongue, this means she must have gotten the recessive allele from that parent. Therefore, the woman's genotype must be heterozygous (Aa), where 'A' represents the dominant allele for tongue rolling, and 'a' represents the recessive allele.
A woman who is a roller with one parent not being able to roll their tongue has a genotype of Aa, making her heterozygous for the trait.