Chimera and other fertilization errors

Clin Genet. 2006 Nov;70(5):363-73. doi: 10.1111/j.1399-0004.2006.00689.x.


The finding of a mixture of 46,XX and 46,XY cells in an individual has been rarely reported in literature. It usually results in individuals with ambiguous genitalia. Approximately 10% of true human hermaphrodites show this type of karyotype. However, the underlying mechanisms are poorly understood. It may be the result of mosaicism or chimerism. By definition, a chimera is produced by the fusion of two different zygotes in a single embryo, while a mosaic contains genetically different cells issued from a single zygote. Several mechanisms are involved in the production of chimera. Stricto sensu, chimerism occurs from the post-zygotic fusion of two distinct embryos leading to a tetragametic chimera. In addition, there are other entities, which are also referred to as chimera: parthenogenetic chimera and chimera resulting from fertilization of the second polar body. Furthermore, a particular type of chimera called 'androgenetic chimera' recently described in fetuses with placental mesenchymal dysplasia and in rare patients with Beckwith-Wiedemann syndrome is discussed. Strategies to study mechanisms leading to the production of chimera and mosaics are also proposed.

Publication types

  • Review

MeSH terms

  • Chimera / genetics*
  • Female
  • Fertilization / genetics*
  • Humans
  • Male
  • Models, Genetic
  • Mosaicism
  • Ovotesticular Disorders of Sex Development / genetics
  • Parthenogenesis / genetics
  • Polyploidy
  • Pregnancy
  • Uniparental Disomy