Complete the following statements by choosing the appropriate option for each blank:
The genotype of a person who cannot roll his tongue is __________.
Topic: Genotype of a non-roller
Try it
Pick an option and check your answer. The full worked answer is below either way.
Answer
(c) rr.
Tongue-rolling is DOMINANT (R) and non-rolling is RECESSIVE (r).
A recessive character shows ONLY in the HOMOZYGOUS RECESSIVE state, because a single dominant allele would mask it. So a non-roller must be rr.
Check the others: RR and Rr both contain at least one R, so both would be ROLLERS — they look identical although their genotypes differ, which is the classic distinction between phenotype and genotype. Option (d) RRr is not a valid genotype at all, since a gene pair has exactly TWO alleles.
THE RULE WORTH CARRYING: whenever someone SHOWS a recessive trait, their genotype is certain — both alleles must be recessive. Someone showing the DOMINANT trait is uncertain: they may be RR or Rr.
rr.