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Gonadal Asymmetry and Sex Determination in Birds

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    Rights statement: Open Access License: This is an Open Access article licensed under the terms of the Creative Commons Attribution-NonCommercial 3.0 Unported license (CC BY-NC) (www.karger.com/OA-license), applicable to the online version of the article only. Distribution permitted for non-commercial purposes only.

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Original languageEnglish
Pages (from-to)227-242
JournalSexual Development
Issue number5
Early online date27 Feb 2014
Publication statusPublished - 2014


Although vertebrates display a superficial bilateral symmetry, most internal organs develop and locate with a consistent left:right asymmetry. There is still considerable debate as to when this process actually begins, but it seems that, at least for some species, the initial steps occur at a very early stage of development. In recent years, a number of model systems, including the chick embryo, have been utilised to increase our understanding of the molecular basis of this complex developmental process. While the basic elements of asymmetry are clearly conserved in chick development, the chick embryo also exhibits an additional unusual asymmetry in terms of the development of the gonads. In the female chick embryo, only 1 gonad and accessory structures fully develop, with the result that the adult hen has only 1 ovary and a single oviduct - both on the left side. With a small number of exceptions, this is a consistent feature of avian development. Here, we describe the morphological development and molecular basis of this unusual asymmetry, consider the implications for avian sex determination, and discuss the possible biological reasons why many birds have adopted a single-ovary system. © 2014 S. Karger AG, Basel.

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