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 entomology. 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. 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.
The cause of this phenomenon is typically, but not always, an event in mitosis during early development. While the organism is only a few cells large, one of the dividing cells does not split its sex chromosomes typically. 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. Usually 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 sexes, the organism has tissue that is female and tissue that is male.
A developmental network theory of how gynandromorphs develop from a single cell based on internetwork links between parental allelic chromosomes is given in. The major types of gynandromorphs, bilateral, polar and oblique are computationally modeled. Many other possible gynandromorph combinations are computationally modeled, including predicted morphologies yet to be discovered. The article relates gynandromorph developmental control networks to how species may form. The models are based on a computational model of bilateral symmetry.
Gynandromorphs occasionally afford a powerful tool in genetic, developmental, and behavioral analyses. In Drosophila melanogaster, for instance, they provided evidence that male courtship behavior originates in the brain, that males can distinguish conspecific females from males by the scent of the posterior, dorsal, integument of females, that the germ cells originate in the posterior-most region of the blastoderm, and that somatic components of the gonads originate in the
mesodermal region of the fourth and fifth abdominal segment.
In his autobiography, Speak, Memory, the writer and lepidopterist Vladimir Nabokov describes a 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.
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- Gouldian finch Erythrura gouldiae Gynandromorph
- Powderhill Banding Fall 2004
- A Gender-bender Colored Cardinal, by Tim Wall, Discovery News, 31 May 2011 
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- Nabokov, Vladimir (1967). Speak, Memory. New York: Alfred A. Knopf. p. 97.
- "Half-cock chicken mystery solved". BBC News. 11 March 2010.
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