Ajay and Vijay are siblings. Ajay can roll his tongue while Vijay cannot. What is the genotype of their parents?

Both the parents are heterozygous dominant.

Reason — Tongue rolling is controlled by a single gene: the dominant allele R allows rolling, while the recessive allele r prevents it.

• Ajay can roll his tongue, so he carries at least one dominant allele (R).
• Vijay cannot roll his tongue, so his genotype must be rr.

For Vijay to receive two recessive alleles (rr), each parent must contribute an r. At the same time, because each parent can roll the tongue themselves, they must also carry an R. Therefore, both parents must be heterozygous Rr.