Question

Alkaptonuria is an infrequent autosomal recessive condition. It is first noticed in newborns when the urine in their diapers turns black upon exposure to air. The condition is caused by the defective transport of the amino acid phenylalanine through the intestinal walls during digestion. About 4 people per 1000 are carriers of alkaptonuria. Sara and James had never heard of alkaptonuria and were shocked to discover that their first child had the condition. Sara's sister Mary and her husband Frank are planning to have a family and are concerned about the possibility of alkaptonuria in one of their children.
The four adults (Sara, James, Mary, and Frank) seek information from a neighbor who is a retired physician.After discussing their family histories, the neighbor says, " I never took genetics, but I know from my many years in practice that Sara and James are both carriers of this recessive condition. Since their first child had the condition, there is a very low chance that the next child will also 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 family history of the condition."The two couples each have babies and both babies have alkaptonuria.

Required:
a. What is the probability that the second child of Mary and Frank will have alkaptonuria?
b. What is the chance that the third child of Sara and James will be free of the condition?
c.The couples are worried that one of their grandchildren will inherit alkaptonuria.
d. What is the chance that a child with alkaptonuria will have an offspring with alkaptonuria if the child's mate has no family history?
e.The couples are worried that one of their grandchildren will inherit alkaptonuria.
f. What is the chance that a child with alkaptonuria will have an offspring with alkaptonuria if the child's mate has no family history?

Answer 1

Answer:

See the answer below

Explanation:

Let the disorder be represented by the allele a.

Since the disease is an autosomal recessive one, affected individuals will have the genotype aa and normal individuals will have the genotype Aa or AA.

Since the four adults are carriers, their genotypes would be Aa.

                    Aa     x     Aa

Progeny:    AA    2Aa    aa

Probability of being affected = 1/4

Probability of being a carrier = 1/2

Probability of not being affected = 3/4

(a) The chance that the child second child of Mary and Frank will have alkaptonuria = 1/2

(b) The chance that  the third child of Sara and James will be free of the condition = 3/4

(c)

(d) If someone has no family history of the disorder, their genotype would be AA.

                 AA     x     aa

                        4 Aa

The chance that a child with alkaptonuria will have an offspring with alkaptonuria if the child's mate has no family history = 0

(e)

(f) The chance that a child with alkaptonuria will have an offspring with alkaptonuria if the child's mate has no family history = 0