Question

Some humans are able to roll their tongue, while others are not. Two parents (both tongue-rollers) have four children, Some of them are tongue rollers and some of them are not. Which of the following statements hold true regarding this?
(i) The allele for tongue-rolling is dominant
(ii) The probability that their next child will be a tongue-roller is 0.5.
(iii) The probability that their next child will not be a tongue-roller is 0.75.
(iv) Both parents have one allele for tongue-rolling and one allele for non-tongue-rolling.

• A. (i) and (iii) only
• B. (i) and (iv) only
• C. (ii) and (iii) only
• D. (ii) and (iv) only

Answer 1

The correct option is B

(i) and (iv) only

In the given case the parents should be heterozygous, for tongue rolling character with genotype Tt. The probability that their next child will be a tongue roller is 0.75 while the probability of not being a tongue roller is 0.25.

Both the parents are heterozygous for the tongue-rolling character (Tt) hence the possibilities of the offspring being a tongue-roller is given in the image. This shows that children carrying the 'T' allele are tongue-rollers, either homozygous or heterozygous and hence we can say tongue-rolling is dominant. The dominant allele is exhibited by both the parents.