An XX/XY sex microchromosome system in a freshwater turtle, Chelodina longicollis (Testudines: Chelidae) with genetic sex determination.
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 approximately 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.
Comparative Genomics Group, Research School of Biological Sciences, The Australian National University, GPO box no. 475, Canberra, ACT 2601, Australia. Tariq.Ezaz@anu.edu.au
Tariq
T
Ezaz
Nicole
N
Valenzuela
Frank
F
Grützner
Ikuo
I
Miura
Arthur
A
Georges
Russell L
RL
Burke
Jennifer A Marshall
JA
Graves
D000818:Animals; D002871:Chromosome Banding; D005260:Female; D007621:Karyotyping; D008297:Male; D009693:Nucleic Acid Hybridization; D012730:Sex Chromosomes / Q000235:genetics*; D019849:Sex Determination Processes; D012733:Sex Differentiation; D013194:Staining and Labeling; D014426:Turtles / Q000235:genetics*