intersex, in biology, an organism having physical characteristics intermediate between a true male and a true female of its species. The condition usually results from extra chromosomes or a hormonal abnormality during embryological development. The sex mosaic, or gynandromorph, is an intersexual organism that has male parts on one side of the body and female parts on the other. Arthropods, mammals, and birds have been known to be gynandromorphic.