Some humans are able to roll their tongue, while others are not. Two parents (both tongue-rollers) have children where not all are tongue-rollers. Which of the following statements hold true regarding this?

The gene for tongue-rolling is dominant.

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The probability that their child will be a tongue-roller is 0.5.

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The probability that their child will not be a tongue-roller is 0.75.

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Both parents are heterozygous for tongue-rolling.

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Solution

The correct options are
A The gene for tongue-rolling is dominant.
D Both parents are heterozygous for tongue-rolling.

Question states that both the parents are tongue-rollers but not all the offspring are tongue-rollers. So, we can conclude that parents are heterozygous for the character.

So the genotype for parents will be Tt (heterozygous for tongue-rolling) where T is dominant and t is a recessive character.

Out of the 4 possible offsprings, the probability that their child will be a tongue-roller is 0.75 (3/4), while the probability of not being a tongue-roller is 0.25 (1/4).

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Similar questions

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.

Q. Some humans are able to roll their tongue, while others are not. Two parents (both tongue-rollers) have four children, all of whom are not tongue-rollers. 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.

Q. Some people have blue eyes, while others have brown. Two parents both having brown eyes have two children with blue eyes. Which of the following statements hold true regarding this?

In humans, the ability to roll the tongue is a dominant trait. The inability to roll the tongue is a recessive trait. If two individuals homozygous recessive for this trait have a child, what is the chance that the child will be able to roll his tongue?

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