Question

A man with cystic fibrosis of the pancreas wishes to marry a young woman whose family has never had an individual born with the disorder. Cystic fibrosis is an inborn error of metabolism, a recessive condition, in which an enzyme necessary for fat digestion is lacking. Could this couple have a child with cystic fibrosis? Write all of the possible genotypes for the genotypes for the man, the woman, and the children that they may have should they marry.

Answer 1

Cystic fibrosis is a recessive condition; meaning if a dominant condition takes over it will not be seen in the offspring. The man genotype with cystic fibrosis can only be this: cc (when c is equal to the cystic fibrosis and C is equal to not having one). The woman with no history of cystic fibrosis can possibly have either of these two genotypes: Cc or CC.

To see their offspring’s possible genotype, we’ll use a punnett square let’s start with Cc:

                C             c

c              Cc           cc

c              Cc           cc            There is a 50 % chance of the child having cystic fibrosis.

To see their offsprings possible genotype with CC:

                C             C

c              Cc           Cc

c              Cc           Cc           There is no chance that the child will have cystic fibrosis.