Double heterozygote: An individual who is heterozygous at two loci under investigation.
This differs from double heterozygote, which refers to an individual who is heterozygous for mutations at two separate genetic loci, which together manifest disease.
The term proposed by Haldane (1941), by analogy with chemical isomerism, to describe a double heterozygote in coupling phase, that is, with the two dominant factors derived from one parent and the two recessives from the other.
When gametes form in double heterozygotes (for example, a green/yellow–round/wrinkled plant), these genes assort independently, because the two chromosomes that bear them assort independently.
See also: Heterozygote, Sequence, Chromosome, Trans, DNA