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?

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.

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.