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Do sex chromosomes of snakes, monitor lizards, and iguanian lizards result from multiple fission of an “ancestral amniote super-sex chromosome”?


Sex chromosomes in some amniotes share linkage homologies with distantly related taxa in regions orthologous to squamate reptile chromosome 2 (SR2) and the snake W sex chromosome. Thus, the SR2 and W chromosomes may formerly have been part of a larger ancestral amniote super-sex chromosome. Comparison of various sex chromosomal linkage homologies in Toxicofera with those in other amniotes offers an excellent model to assess key cytological differences, to understand the mechanisms of amniote sex chromosome evolution in each lineage and the existence of an ancestral amniote super-sex chromosome. Chromosome maps of four species of Toxicofera were constructed using bacterial artificial chromosomes (BACs) derived from chicken and zebra finch libraries containing amniote sex chromosomal linkages. Different macrochromosome linkage homologies were highly conserved among Toxicofera, and at least two BACs (CH261-125F1 and CH261-40D6) showed partial homology with sex chromosomes of amniotes associated with SR2, which supports the hypothesis of an ancestral super-sex chromosome with overlaps of partial linkage homologies. The present data also suggest a possible multiple fission mechanism of an ancestral super-sex chromosome, which resulted in further development of various sex chromosomal linkages of Toxicofera based on particular properties that favored the role of sex chromosomes.

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Anolis carolinensis


Apalone spinifera


Bacterial artificial chromosomes


Calotes versicolor




Ethylenediaminetetraacetic acid


Elaphe quadrivirgata


Fetal bovine serum


Fluorescent in situ hybridization


Fluorescein isothiocyanate


Gallus gallus


Gekko hokouensis


Glyptemys insculpta


Genotypic sex determination


Homo sapiens


Lacerta agilis


Leiolepis reevesii rubritaeniata


Macropus eugenii


Naja kaouthia


Ornithorhynchus anatinus


Pelodiscus sinensis


Pogona vitticeps


Queen Saovabha Memorial Institute


Siebenrockiella crassicollis


Staurotypus salvinii


Staurotypus triporcatus


Taeniopygia guttata


Temperature sex determination


Takydromus sexlineatus


Varanus komodoensis


Varanus salvator macromaculatus


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We extend grateful thanks to Lawan Chanhome, Tanapong Tawan, Taksa Vasaruchapong, and Panithi Laoungbua (Snake Farm, Queen Saovabha Memorial Institute, Thai Red Cross Society, Thailand) and the Conservation Research and Education Division, Zoological Park Organization, Dusit, Bangkok, Thailand, for help with sample collection and advice on sample preparation.

Availability of data and material

The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.


This study was financially supported by grants from the Center for Advanced Studies in Tropical Natural Resources, National Research University-Kasetsart University (CASTNAR, NRU-KU, Thailand) (nos. 6/2558 and 9/2559) awarded to KS, Thailand Research Fund (TRF) (nos. RSA6180075 and PHD60I0014) awarded to KS and WS, Thailand Research Fund-Newton Fund Ph.D. Placement (no. GA/PhD/scholar/Year5/007) awarded to WS, and the Thailand Research Fund-Newton Fund Placement, Travel Grant for PhD Supervisors (GA/PhD/Sup/Year4/003) awarded to KS. This work was also funded in part by the Biotechnology and Biological Sciences Research Council (BB/K008161/1) to the University of Kent (DKG).

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W.S. and K.S. drafted the manuscript; W.S., B.E.O., D.K.G., and K.S. conceived the ideas and designed methodology; W.S. and K.S. carried out the lab work; W.S. and K.S. participated in data analysis; W.S., S.S., N.M., S.B., C.I., P.D., S.P., B.E.O., D.K.G., and K.S. reviewed the data and the manuscript. All authors gave final approval for publication.

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Correspondence to Kornsorn Srikulnath.

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The authors declare that they have no conflict of interest.

Ethics approval

Animal care and all experimental procedures were approved by the Animal Experiment Committee, Kasetsart University, Thailand (approval nos. ACKU61-SCI-021, ACKU61-SCI-023, and ACKU61-SCI-024) and conducted in accordance with the Regulations on Animal Experiments at Kasetsart University.

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Responsible Editor: Fengtang Yang

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Rebecca E O’Connor, Darren K Griffin, and Kornsorn Srikulnath are joint last authors.

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Singchat, W., Sillapaprayoon, S., Muangmai, N. et al. Do sex chromosomes of snakes, monitor lizards, and iguanian lizards result from multiple fission of an “ancestral amniote super-sex chromosome”?. Chromosome Res 28, 209–228 (2020).

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