Chapter 11, Problem 20QP

The cystic fibrosis gene encodes a chloride channel protein necessary for normal cellular functions. Let us assume that if at least 5% normal channels are present, the affected individual has mild symptoms of cystic fibrosis. Having less than 5% normal channels produces severe symptoms. At least 50% of the channels must be expressed for the individual to be phenotypically normal. This gene has various mutant recessive alleles:

Predict the percent of functional channels and severity of symptoms for the following genotypes:

1. a. heterozygous for CF100
2. b. homozygous for CF100
3. c. heterozygous, with one copy of CF100 and one of CF3
4. d. heterozygous, with one copy of CF1 and one copy of CF3