Cystic fibrosis, which is usually lethal before reproductive ages, is a homozygous recessive disease. Why do cases continue to arise, even though people with the disease rarely live to reproduce?
A. Individuals can pass on the alleles in non-genetic ways, including through the sharing of needles.
B. The harmful allele can reside in heterozygous individuals with few to no negative effects.
C. Mosquitoes can transfer the disease from person to person.
D. Cystic fibrosis is a multifactorial disorder, and is probably controlled by the action of many genes.
Answer: B. The harmful allele can reside in heterozygous individuals with few to no negative effects.
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