Question

Cystic fibrosis is a recessive disorder. Two individuals that are both heterozygous for CF

have children, what percent of their offspring will be affected by the disorder?

Answer 1

Answer: 25%

Explanation: draw out a punnet square. Cross Cc x Cc. (C normal allele) (c Cystic Fibrosis allele). If you draw the punnet square, 1/4 will be cc , 1/4 will be CC, and 1/2 will be Cc. In order for the child to have cystic fibrosis, the genotype must be cc.

Answer 2

For example in cystic fibrosis if both parents are heterozygous, each child has a 25% chance of being born with cystic fibrosis. Some genetic diseases are caused by a dominant gene.