Question

Which of the following statements is true with reference to X-linked recessive traits in human beings?
A. They express equally in both the sexes.
B. They express more in males than in females
C. They express more in females than in males
D. They express only in males

Answer 1

Hint: X-linked or sex-linked is recessive genetic disorders, which are inherited through a genetic defect on an X chromosome.

Complete answer:
 X-linked inheritance means that the gene causing the trait or the disorder is located on the X chromosome.

Option A: In X-linked recessive inheritance, a mutation in a gene on the X chromosome causes the phenotype to be expressed in males (because they have one X and one Y chromosome).

Option B: In X-linked recessive inheritance, a mutation in a gene on the X chromosome causes the phenotype to be expressed in males (because they have one X and one Y chromosome). Females who are homozygous for the gene mutation. Females have two X chromosomes, while males have one X and one Y chromosome. Carrier females who have only one copy of the mutation do not usually express the phenotype, although differences in X chromosome inactivation can lead to varying degrees of clinical expression in carrier females since some cells will express one X allele and some will express the other.

Option C: X-linked inheritance means that the gene causing the trait or the disorder is located on the X chromosome. Carrier females who have only one copy of the mutation do not usually express the phenotype, although differences in X chromosome inactivation can lead to varying degrees of clinical expression in carrier females since some cells will express one X allele and some will express the other.

Option D: X-linked inheritance causes the phenotype to be expressed more in males. It is commonly expressed in males than in females. It is due to the fact that males possess only a single X chromosome, and therefore require only one mutated X in order to be affected. Women possess two X chromosomes and thus must receive two of the mutated recessive X chromosomes.

Therefore, B is the correct option.

Note: It is to be noted that, X-linked recessive traits tend to skip generations, meaning an affected grandfather will not have an affected son but could have an affected grandson through his daughter.