trisomic

An organism with an extra chromosome in addition to the normal complement, i.e. 2n+1. Trisomy typically arises when a normal gamete (n) fuses with one containing an extra chromosome (n + 1). The extra chromosome may be a simple copy of one of the chromosomes (primary trisomic), an *isochromosome (secondary trisomic), or may include parts of two nonhomologous chromosomes (tertiary trisomic). Trisomics often have abnormal phenotypes and are frequently less fertile than diploids. See aneuploidy.