Hemizygote

Hemizygous describes a diploid individual who has only one allele of a gene or chromosome segment rather than the usual two. For organisms where the male is heterogametic, such as humans, it refers in particular to X-linked genes, since males normally possess only one X chromosome. They are hemizygous for (nearly) all genes that are located on the X-chromosome.

A hemizygote therefore refers to a cell or organism whose genome includes only one allele for a given trait.