Polydactylism is a dominant trait that results in extra fingers and toes in humans. A polydactyl man marries a woman with 10 fingers and toes. They have a child that has a normal number of digits. The phenotype of the man's father is unknown, but his mother has a normal phenotype. What are the genotypes of the married couple?.

Question

Biology

Malcolm Kaufman

4 January, 10:09

Polydactylism is a dominant trait that results in extra fingers and toes in humans. A polydactyl man marries a woman with 10 fingers and toes. They have a child that has a normal number of digits. The phenotype of the man's father is unknown, but his mother has a normal phenotype. What are the genotypes of the married couple?.

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Answers (1)

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Christensen · Answer 1

The man is heterozygous and the wife must be a homozygous normal individual.

Explanation:

Since the woman is not polydactyl so it is obvious that she does not has the allele for polydactylism on any of the chromosome. Otherwise being dominant, it must have expressed itself.

The man shows polydactylism so it is obvious that he has the allele either on one chromosome or both chromosomes i. e. he may be a homozygous or heterozygous.

But the child does not show polydactylism, this confirms that it does not have the allele on any of the chromosome.

We know that a child recieves half set of fathers chromosomes and half set of mothers chromosome that form the homologous pairs.

For the child to be homozygous, he must not have received the polydactylism allele from either of the parent. This is possible if and only if the father had a non defective allele. So we conclude that father is heterozygous.