1. Having only one copy of a particular gene or allele, typically because it is located on a sex chromosome (such as the X chromosome in males) where there is no corresponding allele on the homologous chromosome.
Usage: genetics; technical

Examples

• Male mammals are hemizygous for genes on the X chromosome because they have only one X chromosome.
• A hemizygous male will express any recessive allele present on his single X chromosome.
• The hemizygous condition in males makes X-linked traits appear more frequently than in females.
• Hemizygous individuals carry only one copy of a gene instead of the typical two copies.
• Color blindness is more common in hemizygous males than in heterozygous females.