Gynandromorphism


Gynandromorphism is the phenomenon that occurs when an individual organism possesses both male and female phenotypes due to genetic chimera of sex chromosomes in cells across the body and is most easily recognized in species that display sexual dimorphism. An individual who displays this characteristic is called a gynandromorph. The term comes from the Greek γυνή 'female', ἀνήρ 'male', and μορφή 'form', and is most commonly documented within the field of entomology. Gynandromorphism is distinct from both intersexuality and hermaphroditism, although the terms are sometimes used interchangeably.

Occurrence

Gynandromorphism has been noted in Lepidoptera since the 1700s. It has also been observed in crustaceans, such as lobsters and crabs, in spiders, ticks, flies, locusts, crickets, dragonflies, ants, termites, bees, lizards, snakes, rodents, and birds. Although it can be seen in a variety of species, gynandromorphism is notably uncommon. Reporting depends on ease of detecting the phenomenon and how well-studied a region or organism is. For example, up until 2023 gynandromorphism had been reported in more than 40 bird species, but the vast majority of these are from the Palearctic and Nearctic; meanwhile, incidents in species from other regions may go underreported due to lack of data collection.

Pattern of distribution of male and female tissues in a single organism

Several patterns of tissue distribution occur amongst observed gynandromorphs. Patch-like patterns may arise, but commonly the phenotype presents in a symmetrical pattern, of which there are three main types: bilateral, oblique, and transverse. Bilateral describes an organism that is split laterally with one side possessing female characteristics and the other having male characteristics. Oblique refers to a diagonal line across the sagittal plane that separates the male and female phenotypes. Lastly, transverse is a separation of male and female phenotypes along an axis that intersects with what would be considered the primary axis for the body of a given organism.
A notable example in birds is the zebra finch. These birds have lateralized brain structures in the face of a common steroid signal, providing strong evidence for a non-hormonal primary sex mechanism regulating brain differentiation.

Causes

The exact cause for gynandromorphism is unknown, and appears to vary by species. One proposed cause for the phenotype in birds is a disruption that occurs in meiosis in female birds -- who possess ZW chromosomes -- in which polar bodies are not forced out of the cell. This is then followed with fertilization by two Z-bearing sperm cells which creates cells in the embryo containing both ZZ and ZW chromosomes. The same phenomenon can be seen in other species, such as Drosophila melanogaster, and creates a genetic mosaic which gives rise to the mixed phenotype.

As a research tool

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 or some other characteristic 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.