Question

Imagine that you are a genetic counselor, and a couple planning to start a family comes to you for information. Charles was married once before, and he and his first wife had a child with cystic fibrosis. The brother of his current wife, Elaine, died of cystic fibrosis. What is the probability that Charles and Elaine will have a baby with cystic fibrosis? (Neither Charles nor Elaine has cystic fibrosis.)

Answer 1

The probability of Charles and Elaine having a baby with cystic fibrosis is 25%. The disease is autosomal recessive, meaning both parents must carry a faulty allele. Based on their family history, Charles is a carrier because he had a child with cystic fibrosis, and Elaine has the potential to carry the gene because her brother had the disease.

Step-by-step explanation:

The probability of Charles and Elaine having a baby with cystic fibrosis can be determined by analyzing their family history. Charles had a child with cystic fibrosis in his previous marriage, and Elaine's brother died of cystic fibrosis.

Cystic fibrosis is an autosomal recessive genetic disorder. This means that both parents must carry a faulty allele in order to have a child with the disease. Based on this, Charles is a carrier because he had a child with cystic fibrosis. Elaine, being the sister of an individual who had cystic fibrosis, also has the potential to carry the gene.

To determine the probability, we can use a Punnett square. If both Charles and Elaine are carriers (heterozygous), there is a 25% chance that their child will inherit two recessive alleles and have cystic fibrosis. However, there is a 75% chance that their child will be a carrier without any symptoms of the disease.