What is a hemizygote?

A hemizygote refers to an individual with a single allele for a given gene instead of the typical two alleles. This condition is most commonly observed in males for genes located on the X chromosome because males have one X and one Y chromosome, meaning they will possess only one copy of the genes located on the X. If a mutation occurs in a gene located on the X chromosome in a male, he is said to be hemizygous for that gene, as he has no second allele to complement or mask the mutation.

In the context of the choices given, a hemizygote specifically relates to a male with a mutant allele for a gene on the Y chromosome – as such genes show a difference in expression compared to females, who have two X chromosomes and can therefore potentially have a normal allele to counter a mutation. This distinction highlights the genetic framework where hemizygosity plays a crucial role, particularly in the understanding of X-linked traits and disorders.