Question

How could two people with albinism have a child who has normal skin pigment?

Short answer

Two people with albinism could have a child with normal skin pigmentation if there was a mutation in one of the parent's gametes that changed the recessive albino allele (a) to a dominant normal pigment allele (A). The child could then inherit this A allele and have normal skin pigment.

Step-by-step solution

Understanding the Basics

Albinism is caused by a recessive allele. This means an individual must have two copies of the recessive allele to exhibit the condition. Albinos have the genotype aa, which means both of their alleles are recessive.

Analysis of the Initial Conditions

If two people with albinism (aa) have a child, their offspring can only inherit the a allele from each parent, because the parents only have the a allele to pass on. This would result in a child with the genotype aa, which is albino.

Resolving the Paradox

However, the question suggests that the child has normal skin pigment, which seems contrary to the rules of genetic inheritance. This scenario could only be possible if there has been a mutation, meaning the allele changes from recessive (a) to dominant (A) in the gametes of one or both parents before or during conception.

Concluding the Results

If a mutation occurred in one of the parent's gametes, changing their a allele to a dominant A, the child could inherit this A allele and end up with the genotype Aa, giving them normal skin pigment, despite both their parents having albinism. Such spontaneous mutations are relatively rare and are the result of errors during DNA replication or damage from environmental factors.