In humans, tongue rolling is a dominant trait; those with the recessive condition cannot roll their tongues. Grant can roll his tongue; but his mother could not: What is Grant’s genotype?
The correct answer and explanation is:
The correct answer is that Grant’s genotype must be heterozygous (Rr).
Explanation:
Tongue rolling is a classic example of a trait determined by a single gene with two alleles, where the ability to roll the tongue (R) is dominant, and the inability to roll the tongue (r) is recessive. A person who can roll their tongue can have either the genotype RR (homozygous dominant) or Rr (heterozygous). A person who cannot roll their tongue must have the genotype rr (homozygous recessive).
In this case, Grant can roll his tongue, so his genotype could be either RR or Rr. However, Grant’s mother cannot roll her tongue, which means she must have the genotype rr.
For Grant to inherit the ability to roll his tongue from a mother who cannot roll hers (rr), Grant must have inherited one recessive allele (r) from his mother. Since Grant can roll his tongue, he must have at least one dominant allele (R) from his father. Therefore, Grant’s genotype must be Rr.
This means Grant carries one dominant allele for tongue rolling and one recessive allele. If Grant were homozygous dominant (RR), he would not carry the recessive allele and it would be impossible for his mother, who is rr, to pass on an r allele to him. Since the mother has two recessive alleles, she can only pass on an r allele, making it impossible for Grant to be RR.
Thus, Grant’s genotype is heterozygous (Rr), explaining how he can roll his tongue while his mother cannot. This classic inheritance pattern illustrates simple Mendelian genetics where dominant and recessive alleles determine observable traits, and carriers of dominant traits can still pass recessive alleles to their offspring.