In humans, tongue rolling is dominant over non-rolling. A man who can roll his tongue marries a woman who cannot. They have 8 children, of which 6 can roll their tongue. What is the genotype of these 6 children?
A
Rr
B
rr
C
RR
D
6R
The correct answer is A. Rr.
Tongue rolling is determined by a single gene with two alleles - the "rolling" allele (R) and the "non-rolling" allele (r). Since tongue rolling is dominant over non-rolling, individuals with either RR or Rr genotypes will be able to roll their tongue.
The man can roll his tongue, so his genotype must include at least one copy of the rolling allele. We don't know whether he is homozygous (RR) or heterozygous (Rr), but since the question does not specify, we assume he is heterozygous (Rr) as it is the most common scenario.
The woman cannot roll her tongue, so her genotype must be rr.
When these two individuals have children, each child has a 50% chance of inheriting the rolling allele (R) from the father and a 50% chance of inheriting the non-rolling allele (r) from the mother.
Out of the 8 children, 6 can roll their tongue. This means that these 6 children must have at least one rolling allele.
Since the woman cannot contribute the rolling allele (r), all 6 of the children must have inherited the rolling allele (R) from the father.
Therefore, the genotype of the 6 children who can roll their tongue is Rr.