Question

A couple is planning to start a family and is concerned about having a child with cystic fibrosis, an autosomal recessive disorder. Both the husband and wife are healthy (do not have cysticfibrosis), but each has a sibling with this disorder. Genetic testing shows that only the wife carries one copy of the cystic fibrosis allele. Should this couple worry about having a child withcystic fibrosis?A.Yes, since the wife can pass down the cystic fibrosis allele, their child can have cystic fibrosis.B.No, since the husband has no cystic fibrosis allele to pass dowm, their child will not have cystic fibrosisC.Yes, since both the husband and wife have siblings with this disorder, their child can have cystic fibrosis.D.No, since this disorder can be passed down only from father to offspring, their child will not have cystic fibrosis.

Answer 1

Cystic Fibrosis

Cystic fibrosis is a genetic disease caused by the presence of two autosomal recessive alleles. It is a disease characterized by increasing the thickness of mucus, causing problems in the respiratory and digestive systems.

As it is a recessive disease, we need to understand that a recessive allele will only be expressed when there are two copies of the allele, that is:

• Dominant disease,: manifests when there are two dominant alleles (AA) or one dominant allele and one recessive allele (Aa)

,

• Recessive disease,: manifests only when both recessive alleles (aa) are present.

Analyzing the exercise, it is possible to notice that in the couple's family, both individuals have cases of cystic fibrosis in the family, but none of them manifested it, so we deduce that the man and the woman have -at least- 1 dominant allele.

The examination showed that only the woman is a carrier of the recessive gene. Therefore, the couple's genotype is:

• Woman: Aa;

,

• Man: AA.

Therefore, we can say that alternative "B" is the answer.