Question

A child with cystic fibrosis can be born to two parents who do not have the disease, but both have the heterozygous genotype. This is because the disease _____.
A. Occurs in individuals who received one allele from one or both parents
B. Is caused by having 2 copies of a recessive allele
C. Is caused by a dominant allele
D. requires certain environmental conditions to be expressed

Answer 1

The correct answer is B. Cystic fibrosis is caused by having two copies of a recessive allele, one inherited from each parent. A child with cystic fibrosis can be born to two parents who do not have the disease, but both have the heterozygous genotype. In this case, each parent has one copy of the normal allele and one copy of the recessive allele. They are carriers of the disease but do not have symptoms because the normal allele is dominant. However, when they have children, there is a 25% chance that the child will inherit two copies of the recessive allele and therefore have cystic fibrosis. This is why cystic fibrosis is considered a recessive genetic disorder.

Answer 2

B.

Answer 3

The answer is B.

Answer 4

That's true, However,
People with one CF gene are called carriers. If a parent is a carrier, there's a 50 percent chance they'll pass on the gene with a mutation to their child. If both parents pass on a normal gene, or only one parent passes a gene with a mutation, the child will not have CF.