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An XX/XY sex microchromosome system in a freshwater turtle, Chelodina longicollis (Testudines: Chelidae) with genetic sex determination

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Abstract

Heteromorphic sex chromosomes are rare in turtles, having been described in only four species. Like many turtle species, the Australian freshwater turtle Chelodina longicollis has genetic sex determination, but no distinguishable (heteromorphic) sex chromosomes were identified in a previous karyotyping study. We used comparative genomic hybridization (CGH) to show that C. longicollis has an XX/XY system of chromosomal sex determination, involving a pair of microchromosomes. C-banding and reverse fluorescent staining also distinguished microchromosomes with different banding patterns in males and females in ∼70% cells examined. GTG-banding did not reveal any heteromorphic chromosomes, and no replication asynchrony on the X or Y microchromosomes was observed using replication banding. We conclude that there is a very small sequence difference between X and Y chromosomes in this species, a difference that is consistently detectable only by high-resolution molecular cytogenetic techniques, such as CGH. This is the first time a pair of microchromosomes has been identified as the sex chromosomes in a turtle species.

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Authors and Affiliations

  1. Comparative Genomics Group, Research School of Biological Sciences, The Australian National University, GPO box no. 475, Canberra, ACT 2601, Australia

    Tariq Ezaz, Frank Grützner & Jennifer A. Marshall Graves

  2. Department of Ecology, Evolution, and Organismal Biology, Iowa State University, 239 Bessey Hall, Ames, IA, 50011, USA

    Nicole Valenzuela

  3. Institute for Amphibian Biology, Graduate School of Science, Hiroshima University, 1-1-1 Kagamiyama, Higashi-Hiroshima, Hiroshima, 739-8526, Japan

    Ikuo Miura

  4. Institute for Applied Ecology, University of Canberra, Canberra, ACT 2601, Australia

    Arthur Georges

  5. Department of Biology, Hofstra University, Hempstead, NY, 11549, USA

    Russell L. Burke

Authors
  1. Tariq Ezaz
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  2. Nicole Valenzuela
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  3. Frank Grützner
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  4. Ikuo Miura
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  5. Arthur Georges
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  6. Russell L. Burke
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  7. Jennifer A. Marshall Graves
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Correspondence to Tariq Ezaz.

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Ezaz, T., Valenzuela, N., Grützner, F. et al. An XX/XY sex microchromosome system in a freshwater turtle, Chelodina longicollis (Testudines: Chelidae) with genetic sex determination. Chromosome Res 14, 139–150 (2006). https://doi.org/10.1007/s10577-006-1029-6

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  • DOI: https://doi.org/10.1007/s10577-006-1029-6

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