Definition
noun
A gene in which it has no allelic counterpart or is present as only a single copy instead of the usual two copies in a diploid cell or organism.
Supplement
For example, a gene wherein one of its pair is deleted is a hemizygous gene. In another example, most of the genes of the X chromosome and Y chromosome in human males are hemizygous since males have only one X chromosome (and one Y chromosome) (unlike females that has two X chromosomes).
Word origin: Greek hēmi- half + zygous > zygote.
Dictionary > Hemizygous gene
