Question

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.

Explanation:

Cystic fibrosis is a recessive genetic disorder. Parents with at least one recessive allele (genotype likely heterozygous, e.g., Aa) can pass either dominant (A) or recessive (a) alleles. For a child to have the disease, they need two recessive alleles (aa). Each parent can pass a recessive allele, so the child may get two recessives (have disease) or not (if at least one dominant is passed). Option 1 is wrong (recessives can be passed), option 2 is wrong (dominants can be passed), option 4 is wrong (disease depends on alleles). Option 3 correctly explains the likelihood.

Answer:

The child may or may not have the disease because a recessive gene from each parent may be passed on.