Cystic fibrosis is the most common fatal genetic disorder in humans. It is caused by recessive mutations in the CFTR gene, which encodes a membrane protein that regulates chloride ion transport. The mutations lead to partial of complete loss-of-function of the membrane protein. About 1 in 23 Caucasians carry a mutant allele. Given the devastating consequences of mutation in the CFTR gene, scientists have wondered why mutant alleles are not more rare. One hypothesis why mutations are relatively frequent is that heterozygotes are more resistant to cholera. If this hypothesis is correct, then mutant alleles at the CFTR gene would show partial dominance. overdominance. negative dominance. incomplete dominance. dominance.
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Cystic fibrosis (CF) is caused by a genetic mutation resulting in defective proteins in secretory cells, mainly in the epithelial lining of the respiratory tract. The one in every 2,000 Caucasian babies who has the disease is homozygous for the recessive mutant. Although medical treatment is becoming more effective, in the past, most children with CF died before their teens. About 20 Caucasian in 2,000 are carriers of the trait, having one mutant and one normal allele, but they do not develop the disease. According to rules of population genetics, the frequency of the homozygous recessive genotype should be rarer than it is. What is one possible explanation for the unusually high frequency of this allele in Caucasian population?
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Cystic fibrosis is a genetic disorder. It is a recessive trait that is determined by two alleles. Suppose two parents each carry at least one recessive allele, but neither of them has cystic fibrosis. Which statement reflects the likelihood of a child of these parents having cystic fibrosis? The child cannot have the disease because only the dominant alleles will be passed on. The child will have the disease because only recessive alleles will be passed on. The child may or may not have the disease because a recessive gene from each parent may be passed on. The child may or may not have the disease because the disease does not depend on the alleles of the parents.
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