Patti is passing on a mutated gene on her X chromosome. Why is her son more likely to express the mutation in his phenotype than her daughter is?

Males are hemizyguos for X-linked genes and express all the X-linked genes present in their genome.

Explanation:

Human males have one copy of the X chromosome and one copy of the Y chromosome as their sex chromosome. Therefore, a human male expresses all the X-linked alleles present in its X chromosome irrespective of their dominant or recessive nature in females. The absence of a second copy of the X-linked genes in males allows the expression of these genes.

On the other hand, females have two copies of X chromosomes as their sex chromosomes. The presence of one copy of wild type allele may mask the expression of the mutant allele in females. Therefore, males are more likely to express an X-linked mutant gene than females.