Alkaptonuria is an uncommon autosomal recessive condition. Sara and James had never heard of alkaptonuria, and...

Alkaptonuria is an uncommon autosomal recessive condition. Sara and James had never heard of alkaptonuria, and were shocked when their first child was born with the condition. Sara’s sister, Mary, and her husband, Frank, are also planning to have a family. Mary and Frank are concerned about the possibility of alkaptonuria affecting their children. The four adults (Sara, James, Mary, and Frank) seek the advice of a neighbor who is a retired physician. After discussing the family histories, the neighbour says, “I never took genetics, but I know that Sara and James must be carriers of this recessive condition. Since their first child has the condition, there is a very low chance that the next child will have it, because the odds of having two children with a recessive condition are very low. Mary and Frank have no chance of having a child with alkaptonuria, because Frank has no history of the condition.” The two couples each have a baby, and bothbabies have alkaptonuria.

What are the genotypes of the four adults?
What was the incorrect information given to Sara and James, and what is the correct information that they should have been provided?
What was the incorrect information given to Mary and Frank, and what is the correct information that they should have been provided?

Solutions

Expert Solution

a. All 4 adults are carriers of the recessive allele and therefore must be heterozygous for the alleles.

b. Sara and James were told that there is a very low chance of having a second child with the same recessive condition which is entirely wrong. The genotype of the child is totally random and every time there's an equal chance of having a child with a recessive condition.

c. Mary and Frank were told that they have no chance of having a child with alkaptonuria because Frank has no history of the condition. Since, it is a recessive condition, having no history doesn't means complete absence of the condition. It could also mean the individual is a carrier of the condition (has a single recessive allele) which turns out to be true in their condition as they get a child with alkaptonuria.

gladiator answered 1 year ago

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