Chapter 2, Problem 3P

Galactosemia is an autosomal recessive disorder caused by the inability to metabolize galactose, a component of the lactose found in mammalian milk. Galactosemia can be partially managed by eliminating dietary intake of lac-tose and galactose. Amanda is healthy, as are her parents, but her brother Alonzo has galactosemia. Brice has a simi-lar family history. He and his parents are healthy, but his sister Brianna has galactosemia. Amanda and Brice are planning a family and seek genetic counseling. Based on the information provided, complete the following activi-ties and answer the questions.

(a) Draw a pedigree that includes Amanda, Brice, and their siblings and parents. Identify the genotype of each person, using G and g to represent the dominant and recessive alleles, respectively.

(b) What is the probability that Amanda is a carrier of the allele for galactosemia? What is the probability that Brice is a carrier? Explain your reasoning for each answer.

(c) What is the probability that the first child of Amanda and Brice will have galactosemia? Show your work.

(d) If the first child has galactosemia, what is the prob-ability that the second child will have galactosemia? Explain the reasoning for your answer.