(1) Of, or pertaining to an individual (or a condition in a cell or an organism) containing two different alleles for a particular trait.
(2) Having dissimilar alleles that code for the same gene or trait.
Example: a zygote having one dominant allele and one recessive allele, i.e. Aa, for a particular trait.
Word origin: G. héteros the other of two, other, different + zygous, which pertains to a zygote.
Related forms: heterozygosity (noun).
Related phrases: heterozygous recessive, heterozygous dominant.
See also: allele.