Chromosome Research

, Volume 14, Issue 2, pp 139–150 | Cite as

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

  • Tariq EzazEmail author
  • Nicole Valenzuela
  • Frank Grützner
  • Ikuo Miura
  • Arthur Georges
  • Russell L. Burke
  • Jennifer A. Marshall Graves


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.

Key words

CGH Chelodina longicollis comparative genomic hybridization eastern snake-necked turtle microchromosomes sex chromosomes 


Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.


  1. Balaresque P, Toupance N, Lluis QM, Crouau-Roy B, Heyer E (2004) Sex-specific selection on the human X chromsosome. Genet Res 83: 169–176.CrossRefPubMedGoogle Scholar
  2. Bickham JW (1975) A cytosystemic study of turtles in the genera Clemys and Sacalia. Herpetologica 31: 198–204.Google Scholar
  3. Barzotti R, Pelliccia F, Rocchi A (2000) Sex chromosome differentiation revealed by genomic in situ hybridization. Chromosom Res 8: 459–464.Google Scholar
  4. Bull JJ, Legler JM (1980) Karyotypes of side-necked turtles (Testudines: Pleurodira). Can J Zool 58: 828–841.Google Scholar
  5. Charlesworth B (1996) The evolution of chromosomal sex determination and dosage compensation. Curr Biol 6: 149–162.PubMedGoogle Scholar
  6. Charlesworth D, Charlesworth B, Marais G (2005) Steps in the evolution of heteromorphic sex chromosomes. Heredity 95: 118–128.Google Scholar
  7. Donnellan SC (1985) The evolution of sex chromosomes in scincid lizards. PhD Thesis, Macquarie University, NSW, Australia.Google Scholar
  8. Ezaz MT, McAndrew BJ, Penman DJ (2004) Spontaneous diploidization of maternal chromosome set in Nile tilapia (Oreochromis niloticus) eggs. Aquac Res 35: 271–277.CrossRefGoogle Scholar
  9. Ezaz T, Quinn AE, Miura I, Sarre SD, Georges A, Graves JAM (2005) The dragon lizard Pogona vitticeps has ZZ/ZW micro-sex chromosomes. Chromosom Res 13: 763–776.Google Scholar
  10. Fitzpatrick MJ (2004) Pleiotropy and the genomic location of sexually selected genes. Am Nat 163: 800–808.CrossRefPubMedGoogle Scholar
  11. Georges A (1988) Sex determination is independent of incubation-temperature in another chelid turtle, Chelodina longicollis. Copeia 1988(1): 248–254.Google Scholar
  12. Gorman GC (1973) The chromosomes of the Reptilia, a cytotaxonomic interpretation. In: Ciarelli AB, Capanna E, eds. Cytotaxonomy and Vertebrate Evolution. London, New York: Academic Press, pp. 349–424.Google Scholar
  13. Graves JAM, Gecz J, Hameister H (2002) Evolution of the human X – a smart and sexy chromosome that controls speciation and development. Cytogenet Genome Res 99: 141–145.Google Scholar
  14. Harlow PS (2001) The ecology of sex-determining mechanisms in Australian agamid lizards. PhD Thesis, School of Biological Sciences. Macquarie University, Sydney.Google Scholar
  15. Janzen FJ, Krenz JG (2004) Phylogenetics: which was first, TSD or GSD? In: Valenzuela N, Lance VA, eds. Temperature Dependent Sex Determination in Vertebrates. Washington DC: Smithsonian Books, pp. 121–130.Google Scholar
  16. Lindholm AK, Brooks R, Breden F (2004) Extreme polymorphism in a Y-linked sexually selected trait. Heredity 92: 156–162.CrossRefPubMedGoogle Scholar
  17. McBee K, Bickham JW, Rhodin AGJ, Mittermeier RA (1985) Karyotypic variation in the genus Platemys (Testudines: Pleurodira). Copeia 1985(2): 445–449.Google Scholar
  18. Miura I (1995) The late replicating banding patterns of chromosomes are highly conserved in the genera Rana, Hyla, and Bufo (Amphibia, Anura). Chromosoma 103: 567–574.PubMedGoogle Scholar
  19. Olmo E (1986) A. Reptilia. In: John B, ed. Animal Cytogenetics 4 Chordata 3. Gebruder Berlin-Stuttgart: Bortraeger.Google Scholar
  20. Olmo E, Cobror O, Morescalchi A, Odierna G (1984) Homomorphic sex chromosomes in lacertid lizard Takydromus sexlineatus. Heredity 53: 457–459.Google Scholar
  21. Olmo E, Signorino G (2005) Chromorep: a reptile chromosomes database. Internet reference retrieved from
  22. Palmer-Allen M, Beynon F, Georges A (1991) Hatchling sex-ratios are independent of temperature in field nests of the long-necked turtle, Chelodina longicollis (Testudinata, Chelidae). Wild Res 18: 225–231.Google Scholar
  23. Ray-Chaudhury SP, Singh L, Sharma T (1971) Evolution of sex chromosomes and formation of W chromatin in snakes. Chromosoma 33: 239–251.Google Scholar
  24. Reeve HK, Pfennig DW (2003) Genetic biases for showy males: Are some genetic systems especially conducive to sexual selection? Proc Natl Acad Sci USA 100:1089–1094.CrossRefPubMedGoogle Scholar
  25. Rice WR (1984) Sex-chromosomes and the evolution of sexual dimorphism. Evolution 38: 735–742.Google Scholar
  26. Sarre SD, Georges A, Quinn A (2004) The ends of a continuum: genetic and temperature-dependent sex determination in reptiles. Bioessays 26: 639–645.CrossRefPubMedGoogle Scholar
  27. Schweizer D (1976) Reverse fluorescent chromosome banding with chromomycin and DAPI. Chromosoma 58: 307–324.CrossRefPubMedGoogle Scholar
  28. Singh L, Purdom IF, Jones KW (1976) Satellite DNA and evolution of sex chromosomes. Chromosoma 76: 137–157.Google Scholar
  29. Sites JW, Bickham JW, Haiduk MW (1979) Derived sex-chromosome in the turtle genus Strurotypus. Science 206: 1410–1412.PubMedGoogle Scholar
  30. Solari AJ (1994) Sex Chromosomes and Sex Determination in Vertebrates, Boca Raton, Florida: CRC Press Inc.Google Scholar
  31. Traut W, Sahara K, Otto TD, Marec F (1999) Molecular differentiation of sex chromosomes probed by comparative genomic hybridization. Chromosoma 108: 173–180.CrossRefPubMedGoogle Scholar
  32. Traut W, Eickhoff U, Schorch J (2001) Identification and analysis of sex chromosomes by comparative genomic hybridization (CGH). Methods Cell Sci 23: 155–161.CrossRefPubMedGoogle Scholar
  33. Uetz P (2005) The EMBL reptile database. Internet references. Retrieved from:, 31 October 2005.Google Scholar
  34. Valenzuela N, Lance VA (2004) Temperature Dependent Sex Determination in Vertebrates. Washington DC: Smithsonian Books.Google Scholar
  35. Valenzuela, N, Adams DC, Janzen FJ (2003) Exactly when is sex environmentally determined? Am Nat 161: 676–683.CrossRefPubMedGoogle Scholar
  36. Verma RS, Babu A (1995) Human Chromosomes: Principles and Techniques. Second Edition. New York: McGraw-Hill, Inc.CrossRefGoogle Scholar
  37. Viets BE, Ewert MA, Talent LG, Nelson CE (1994) Sex determining mechanisms in squamate reptiles. J Exp Zool 270: 45–56.Google Scholar
  38. Witten JG (1983) Some karyotypes of Australian agamids (Reptilia: Lacertilia). Aust J Zoology 31: 533–540.Google Scholar

Copyright information

© Springer 2006

Authors and Affiliations

  • Tariq Ezaz
    • 1
    Email author
  • Nicole Valenzuela
    • 2
  • Frank Grützner
    • 1
  • Ikuo Miura
    • 3
  • Arthur Georges
    • 4
  • Russell L. Burke
    • 5
  • Jennifer A. Marshall Graves
    • 1
  1. 1.Comparative Genomics Group, Research School of Biological SciencesThe Australian National University CanberraAustralia
  2. 2.Department of Ecology, Evolution, and Organismal BiologyIowa State UniversityAmesUSA
  3. 3.Institute for Amphibian Biology, Graduate School of ScienceHiroshima UniversityHiroshimaJapan
  4. 4.Institute for Applied EcologyUniversity of CanberraCanberraAustralia
  5. 5.Department of BiologyHofstra UniversityHempsteadUSA

Personalised recommendations