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The Y chromosome is a sex chromosome found in several vertebrates and mammals, including humans. In addition to 22 pairs of autosomes, the human males have one X chromosome and one Y chromosome. In these organisms, the presence or absence of the Y chromosome determines the development of male traits.
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Updated: Apr 27, 2026

Ex vivo Culture of Drosophila Pupal Testis and Single Male Germ-line Cysts: Dissection, Imaging, and Pharmacological Treatment
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Phallus development in the turtle Trachemys scripta.

Christine E Larkins1, Martin J Cohn

  • 1Department of Molecular Genetics and Microbiology, UF Genetics Institute, University of Florida, Gainesville, Fla., USA.

Sexual Development : Genetics, Molecular Biology, Evolution, Endocrinology, Embryology, and Pathology of Sex Determination and Differentiation
|June 28, 2014
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Summary
This summary is machine-generated.

Amniote phallus development in turtles mirrors mammalian development, suggesting homology. Specialized features like the urethral tube evolved from a common amniote phallus developmental plan.

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Area of Science:

  • Evolutionary developmental biology
  • Comparative anatomy
  • Herpetology

Background:

  • Phallus morphology varies across amniotes, fueling debate on structural homology.
  • Mammalian penises have a closed urethral tube, unlike the open urethral groove (sulcus spermaticus) in reptiles and birds.
  • Homology requires a common developmental origin; different origins suggest re-evolution.

Purpose of the Study:

  • To investigate the evolutionary origins and homology of amniote phallus development.
  • To compare turtle phallus development with that of other amniotes, particularly mammals.
  • To understand the developmental basis of external genitalia evolution in amniotes.

Main Methods:

  • Examined phallus development in the turtle Trachemys scripta.
  • Compared turtle development at tissue, cellular, and molecular levels with mammalian models.
  • Analyzed the embryonic origins and differentiation of phallic structures.

Main Results:

  • Turtle phallus development closely resembles mouse development.
  • Shared developmental patterns observed at tissue, cellular, and molecular levels support phallic homology.
  • Specialized amniote traits, like the mammalian urethral tube, represent lineage-specific modifications of a common developmental plan.

Conclusions:

  • The phalluses of turtles and mammals are likely homologous structures.
  • Amniote phallus development follows a conserved embryonic plan.
  • Evolution of amniote external genitalia involves diversification from a shared developmental blueprint.