Final answer:
A father cannot pass an X-linked gene to his son because he contributes a Y chromosome to male offspring, determining their sex as males. In cases of X-linked recessive inheritance, daughters of Fathers with a normal X chromosome will not be affected, but have a chance to be carriers if their mother also carries the recessive gene.
Step-by-step explanation:
A father cannot pass an X-linked gene to his son. This is because males (XY) only contribute a Y chromosome to their male offspring, which determines the child's sex as male. Fathers do contribute an X chromosome to their daughters, but the question stipulates an X-linked gene, implying a genetic condition. In X-linked recessive inheritance, when the father has a normal X chromosome, his daughters will either be carriers or entirely unaffected, as they can only inherit a recessive gene affecting their X chromosome if their mother contributes the same recessive gene.
For instance, in the pedigree for Color Blindness, which is an X-linked recessive trait, only the mother can pass the recessive allele for the trait to sons. When a female parent is homozygous for a recessive X-linked trait, she will pass the trait on to all of her offspring. Her male offspring must express the trait as they inherit their father's Y chromosome. In contrast, daughters will not be affected unless they inherit an additional recessive gene from their mother, making them unaffected daughters. A pedigree can demonstrate the transmission of such traits and their impact on affected and unaffected individuals across generations.