A pregnant female has been told she is a carrier for fragile X syndrome. She asks, "What does that mean?" The health care provider explains that she is heterozygous for fragile X recessive trait, but this will only be a problem if:

Question

A) The expressed pairing becomes homozygous.
B) The expressed pairing switches to a dominant trait.
C) Her mate also is a carrier of the recessive fragile X trait.
D) She does not receive a blood transfusion from a non–fragile X donor prior to pregnancy.

Answer 1

Ans: A
Feedback:
Offspring in whom the two alleles of a given pair are the same are called homozygotes. For example, a plant may have two alleles for wrinkled peas. Heterozygotes have different alleles at a gene locus. All offspring with a dominant allele manifest that trait. In human genetics, a carrier is a person who is heterozygous for a recessive trait and does not manifest the trait. For example, the gene for the genetic disorder cystic fibrosis is recessive. Therefore, only persons with a genotype having two alleles for cystic fibrosis have the disease. In most cases, neither parent manifests the disease; however, both must be carriers. A blood transfusion will not fix the problem.