Alkaptonuria is a metabolic disorder that results from the autosomal recessive allele a. Individuals who do not have the disease have the dominant allele A.
Nancy, who does not have alkaptonuria, marries Norman, who also does not
have alkaptonuria. Norman’s grandmother (his father’s mother) and Nancy’s
uncle (her mother’s brother) have alkaptonuria. Norman’s grandfather (his
father’s father) does not have the disease and is not a carrier of the alkaptonuria
allele. Neither of Nancy’s maternal grandparents (her mother’s mother and
father) have alkaptonuria. There is no history of alkaptonuria in Norman’s
mother’s family or in Nancy’s father’s family.
a. Draw the pedigree that shows the familial relationships described in the
paragraph above. Use a circle to denote a woman, a square to denote a
man and a filled symbol to show individuals who have the disease
alkaptonuria. In this pedigree, you are attempting to trace the inheritance
of the a allele. Beneath each symbol, show the genotype of each
individual as far as it is known. You may use blanks to indicate that part of
the genotype is unknown, if applicable.
b. What is the probability that Nancy is a carrier of the a allele?
c. What is the probability that Norman is a carrier of the a allele?
d. What is the probability that Nancy and Norman’s first child will have
alkaptonuria?
e. Out of 5 children born to Nancy and Norman, what is the probability that 3
will have alkaptonuria?
f. Out of 4 children born to Nancy and Norman, what is the probability that
at least one will have alkaptonuria?