Question

The ability to curl the tongue is a dominant trait. John cannot curl his tongue, but both of his parents can. List the genotypes for all 3 individuals. Be specific on how you came to your conclusion.

Answer 1

John's genotype must be rr as he expresses the recessive trait and cannot curl his tongue. Both of his parents can curl their tongues, which is a dominant trait, so they must be heterozygous (Rr) as they have passed down the recessive allele to John.

Step-by-step explanation:

The ability to curl one's tongue is a dominant trait. If John cannot curl his tongue and both of his parents can, we can determine their genotypes using the principles of Mendelian genetics. Since John exhibits the recessive trait (not being able to curl his tongue), he must be homozygous recessive, meaning his genotype is rr. His parents can curl their tongues, which is a dominant trait, but since they have produced an offspring with the recessive trait, both parents must carry one recessive allele; hence, they are heterozygous for the trait. Their genotypes must be Rr. We come to this conclusion because for John to express the recessive phenotype, he must have inherited a recessive allele from each of his parents.