In the context of inheritance, what does hemizygous mean?

Hemizygous refers to the condition in which an individual has only one allele for a particular gene that exists on a chromosome. This situation often occurs in organisms with sex chromosomes, especially in males of species such as humans, where the X chromosome carries genes not paired with a corresponding gene on the Y chromosome. For example, in humans, males have one X and one Y chromosome; any genes found on the X chromosome are hemizygous because there is no corresponding allele on the Y chromosome. This means that any mutation or variation in a gene on the X chromosome will be expressed, as there is no second allele to potentially mask its effect.

Other options reflect different genetic concepts that do not align with the definition of hemizygous. Having two alleles for every trait describes a diploid organism, having no alleles for a gene refers to cases of gene deletion or absence which is not typical nomenclature in the context of normal inheritance, and having multiple alleles for a gene pertains to the concept of polymorphic genes, where more than two genetic variants exist in a population, not to hemizygosity.