Final answer:
Males with only one X chromosome are termed hemizygous for X-linked traits, which means a recessive allele on that chromosome will be expressed since there is no corresponding allele on the Y chromosome to mask it.
Step-by-step explanation:
Males are termed hemizygous for X-linked traits since they only have one X chromosome. In human genetics, males have an XY chromosome pair, with the Y chromosome being much shorter and containing many fewer genes than the X chromosome. When a recessive X-linked allele is present, it is always expressed in males because there is no corresponding allele on the Y chromosome that could mask it.
An example of a recessive X-linked trait is red-green color blindness, where affected males are unable to differentiate between the colors red and green. Females, on the other hand, have two X chromosomes, so they must inherit two copies of a recessive allele for the recessive trait to be expressed. They may also be carriers if they inherit one recessive allele and one dominant allele, but they typically do not show symptoms of the trait unless inactivation of the dominant allele occurs.