Final answer:
The inheritance of X-linked traits is shaped by the presence of genes on the sex chromosomes, with males expressing recessive traits with just one copy due to having only one X chromosome, while females require two copies. Recessive X-linked traits are more often seen in males, while females can be unaffected carriers.
Step-by-step explanation:
The inheritance of X-linked traits is distinct from that of other traits due to the unique nature of the sex chromosomes in humans. Sex-linked traits generally refer to traits associated with genes located on the X chromosome. Since females have two X chromosomes (XX) and males have one X and one Y chromosome (XY), the expression of X-linked traits follows different patterns based on one's sex.
For males, there is only one X chromosome, which means they have a single allele for any X-linked gene. Consequently, if a male inherits a recessive X-linked allele for a trait, it will be expressed because there is no dominant allele to mask it. On the other hand, females need to inherit two copies of the recessive allele, one from each parent, to express the recessive trait. This discrepancy explains why X-linked recessive traits are more commonly expressed in males.
X-linked recessive inheritance is notable for the fact that females can be unaffected carriers of a trait, possessing one normal and one mutation-carrying allele, and can pass the latter on to offspring. Thus, if a mother carries an X-linked recessive gene, there is a 50% chance that her sons will be affected and a 50% chance that her daughters will be carriers. Hemophilia, color blindness, and certain forms of muscular dystrophy are examples of conditions inherited in this manner.
Conversely, in the case of X-linked dominant inheritance, female carriers of the dominant X-linked trait will express the condition and can pass the trait to half of their offspring, regardless of sex. The pattern of inheritance depends on whether the affected parent is the mother or the father, and traits can appear in both males and females, albeit differently based on the sex of the progeny and parent.