If a transgene is incorporated into one chromosome of a pair, how is the animal described?

When a transgene is incorporated into one chromosome of a chromosome pair, the animal is described as hemizygous for that specific transgene. This term indicates that the animal possesses only one copy of a gene (in this case, the transgene) instead of the usual two copies found in a diploid organism. This situation commonly occurs in cases of transgenic animals where the introduced gene is present on one of the two homologous chromosomes, leaving the other chromosome without that particular gene.

Other terms such as homozygous and heterozygous refer to the presence of two identical or two different alleles, respectively, at a locus. Haploid describes cells that contain only one complete set of chromosomes, which is not applicable in this context since we are discussing an animal that typically has two sets of chromosomes. Thus, referring to the animal as hemizygous accurately captures the genetic state where the transgene is present on only one chromosome of the pair.