Question 10

A child can inherit a genetic disorder from parents who exhibit no symptoms of the disorder because the disorder is caused by a recessive allele, and each parent carries only a single copy of the allele.

A) The disorder is caused by a recessive allele, and each parent carries only a single copy of the allele.

This option is correct because it describes a situation known as carrier status, where both parents possess one copy of a recessive allele for a genetic disorder but do not express the disorder themselves. When two carriers have a child, there is a 25% chance that the child will inherit both recessive alleles and consequently exhibit the disorder.

B) The disorder is caused by a dominant allele, and each parent carries at least one copy of the allele.

This option is incorrect because if the disorder were caused by a dominant allele, at least one parent would show symptoms of the disorder. Dominant alleles typically manifest in the phenotype if present, meaning that if both parents were carriers of a dominant allele, they would both exhibit symptoms of the disorder.

C) The disorder is caused by multiple genes, and both parents acquired mutations in those genes before the child was born.

This option is incorrect as it suggests that the disorder is polygenic, which can lead to complex inheritance patterns. However, this does not explain how a child could inherit a disorder from asymptomatic parents without a known family history of the disorder, as both parents would need to have the specific mutations for the child to inherit the condition.

D) The disorder is caused by a toxin in the environment, and the parents were exposed to the toxin after the child was born.

This option is incorrect because it implies that environmental factors influence the disorder's inheritance. If the disorder is caused by a toxin, it would not be inherited genetically but rather acquired, meaning the parents could not pass it down to their child in the manner described in the question.

Conclusion

The correct answer, option A, accurately reflects the mechanism of inheritance for many recessive genetic disorders, where asymptomatic carriers can pass on the disorder to their offspring. Other options fail to align with the genetic principles of inheritance, as they either require symptomatic parents or misattribute the cause of the disorder to environmental factors rather than genetic ones.