Janet is homozygous dominant for the wild type allele of the gene that when mutant causes cystic fibrosis. Her brother Henry is a heterozygote. They both do not have the disease cystic fibrosis.

Question

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Since Janet is homozygous dominant, her genotype is not carrying any mutant allele for the cystic fibrosis gene, and so she does not have the disease. Meanwhile, Henry is heterozygous, which means he carries one dominant wild type allele and one recessive mutant allele. However, this is not sufficient for him to develop the disease as it is an autosomal recessive disorder. Hence, both Janet and Henry do not have cystic fibrosis.

Janet Is Homozygous Dominant for the Wild Type Allele of the Gene