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 lactose and galactose. Amanda is healthy, as are her parents, but her brother Alonzo has galactosemia. Brice has a similar 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 activities and answer the questions.

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.

Key Concepts

Autosomal Recessive Inheritance

Autosomal recessive inheritance occurs when a trait or disorder is expressed only when an individual has two copies of the recessive allele, one inherited from each parent. In the case of galactosemia, both parents must be carriers of the recessive allele for their child to be affected. If a child inherits one normal allele and one recessive allele, they will be a carrier but will not show symptoms of the disorder.

Carrier Probability

The probability of being a carrier for a recessive genetic disorder can be calculated using family history and Punnett squares. In this scenario, since Amanda and Brice are healthy but have siblings with galactosemia, they each have a 2 in 3 chance of being carriers. This is because they could either be homozygous dominant (not a carrier), heterozygous (carrier), or homozygous recessive (affected), with the latter being ruled out due to their health.

Genetic Counseling

Genetic counseling provides individuals and families with information about genetic conditions, including risks of inheritance and implications for family planning. In Amanda and Brice's case, genetic counseling will help them understand their carrier status and the likelihood of passing on the allele for galactosemia to their children, guiding their reproductive choices based on their genetic backgrounds.