What does the term hemizygous refer to?

The term hemizygous specifically refers to an individual possessing only one allele for a gene, which is particularly relevant when discussing genes on the X chromosome in males. Males typically have one X and one Y chromosome, meaning they have only one copy of any gene located on the X chromosome. Consequently, if a gene is present on the X chromosome, and there is no corresponding allele on the Y chromosome (since the Y chromosome does not carry that gene), the male will be considered hemizygous for that gene. This concept is essential in understanding patterns of inheritance, particularly for sex-linked traits, where males and females exhibit different behaviors due to their chromosomal configurations.

In contrast, the other options do not accurately define hemizygosity:

• Having two identical alleles (the definition of homozygosity) does not apply here, as hemizygous individuals lack a second allele.

• Being completely homozygous indicates having two identical alleles on both homologous chromosomes, which again does not fit the hemizygous scenario.

• Having multiple genes for one trait refers to polygenic inheritance and does not relate to the concept of hemizygosity, which instead focuses on the number of alleles present for a specific