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First scientific record of two cases of partial twinning in the chick embryo, Gallus gallus domesticus
  1. Maryam Farzaneh1,
  2. Seyed Esmaeil Khoshnam2 and
  3. Mohsen Nokhbatolfoghahai3,4
  1. 1Royan Institute, Tehran, Iran
  2. 2Ahvaz Jondishapour University of Medical Sciences, Ahvaz, Khuzestan, Iran
  3. 3Department of Biology, Shiraz University, Shiraz, Iran
  4. 4MVLS, University of Glasgow, Glasgow, UK
  1. Correspondence to Dr Mohsen Nokhbatolfoghahai, nokhbeh{at}


Bicephalia is one of the scarcest malformations reported in birds and needs to be fully investigated in chick embryos. Among 1500 fertilised eggs used to examine the primordial germ cells in 2-day and 5.5-day chick embryos Gallus gallus domesticus, bicephalia was found and the condition of the heads, the heart and other parts of the body was fully described. Each twin had its own head; hearts were not completely separated from each other and the rest of the bodies were externally unique. This investigation urges others including poultry farms to share their data on a bigger scale. It may also encourage the monitoring of abnormalities randomly seen during early chick embryogenesis and consideration of environmental factors when poultry farms are faced with high percentages of unsuccessful hatching. The report can shed some light on developmental processes and may also help to clarify why bicephalia is not more common.

  • malformation
  • fertilized egg
  • Poultry
  • dicephalic
  • chick development
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  • Contributors MF contributed towards the completion of the project and writing a part of the first draft of the manuscript. SEK helped with the microscopic part of the project as well as contributed to writing the first draft of the manuscript.

  • Competing interests None declared.

  • Provenance and peer review Not commissioned; externally peer reviewed.

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