The right answer is Alleles are passed from the parents’ sex chromosomes to the sex chromosomes in the offspring.
In the case of a so-called X-linked recessive disease, the gene responsible for the disease is on the X chromosome. One of the important consequences of a gene on a sex chromosome is that the disease caused mutation of the gene (definitive transformation of a gene) will affect boys and girls differently. This difference is due to the fact that boys still have only one X chromosome in each cell, which is transmitted to them by their mother, while girls receive an X chromosome from each of their parents and each of their cells involves so two X chromosomes.
