A gynandromorph is an organism that contains both male and female characteristics. The term gynandromorph, from Greek "gyne" female and "andro" male, is mainly used in the field of Lepidopterology (butterfly/moth study) or entomology (all insects). These characteristics can be seen in butterflies, where both male and female characteristics can be seen physically because of sexual dimorphism. Cases of gynandromorphism have also been reported in crustaceans, especially lobsters, sometimes crabs and even in birds.[1][2][3][4] A clear example in birds is the gynandromorphic Zebra Finch. These birds have lateralised brain structures in the face of a common steroid signal, providing strong evidence for a non-hormonal primary sex mechanism regulating brain differentiation.[5]
A gynandromorph can have bilateral asymmetry, one side female and one side male,[6] or they can be mosaic, a case in which the two sexes aren't defined as clearly.
Bilateral gynandromorphy arises very early in development, typically when the organism has between 8 and 64 cells.[7] Later the gynandromorph is mosaic.
The cause of this phenomenon is typically, but not always, an abnormal event in mitosis during early development. While the organism is only a few cells large, one of the dividing cells fails to split its sex chromosomes correctly. This leads to one of the two cells having sex chromosomes that cause male development and the other cell having chromosomes that cause female development. For example, an XY cell undergoing mitosis duplicates its chromosomes, becoming XXYY. Normally this cell would divide into two XY cells, but in rare occasions the cell may divide into an X cell and an XYY cell. If this happens early in development, then a large portion of the cells are X and a large portion are XYY. Since X and XYY dictate different genders, the organism has a chunk of tissue that is female and another chunk that is male. [8]
In his autobiography, Speak, Memory, the writer and lepidopterist Vladimir Nabokov describes a beautiful gynandromorph butterfly, male on one side, female on the other, that he caught as a youth on his family's Russian estate.
Chickens can also be gynandromorphous.[9]