Agamid lizards are squamate reptiles which show diverse sex determination systems. As the pivotal agamid model, the bearded dragon (Pogona vitticeps, PVI) exhibits ZZ/ZW micro-sex chromosomes, whereas the sex chromosome system and sex linked genes of several agamids remain unknown. To investigate bearded dragon sex chromosome homology, cross-species BAC-FISH mapping was performed in Calotes versicolor (CVE) and Amphibolurus muricatus (AMU) using three BAC clones containing genes from PVI ZW sex chromosomes. Results showed that two BAC clones 3L7 and 150H19 were localized to regions adjacent to NOR of CVE2q and one pair of CVE microchromosomes, respectively, while all BACs were mapped to the same microchromosomes of AMU. Notably, 3L7 was also located on the region adjacent to NOR AMU2q. This suggests that the presence of microchromosomes in CVE and AMU resulted from chromosomal fission adjacent to NOR near the telomeric site of chromosome 2, and subsequent fusion with a proto microchromosome. These rearrangements collectively support our previous reports on mapping in other dragon lizards that the bearded dragon ZW pair shared common ancestry with squamate reptile chromosome 2, which now shows partial homology with the chicken Z chromosome. This supports our previous hypothesis of existence of an ancestral super-sex chromosome in amniotes.
Agamid lizards are squamate reptiles which show diverse sex determination systems. As the pivotal agamid model, the bearded dragon (Pogona vitticeps, PVI) exhibits ZZ/ZW micro-sex chromosomes, whereas the sex chromosome system and sex linked genes of several agamids remain unknown. To investigate bearded dragon sex chromosome homology, cross-species BAC-FISH mapping was performed in Calotes versicolor (CVE) and Amphibolurus muricatus (AMU) using three BAC clones containing genes from PVI ZW sex chromosomes. Results showed that two BAC clones 3L7 and 150H19 were localized to regions adjacent to NOR of CVE2q and one pair of CVE microchromosomes, respectively, while all BACs were mapped to the same microchromosomes of AMU. Notably, 3L7 was also located on the region adjacent to NOR AMU2q. This suggests that the presence of microchromosomes in CVE and AMU resulted from chromosomal fission adjacent to NOR near the telomeric site of chromosome 2, and subsequent fusion with a proto microchromosome. These rearrangements collectively support our previous reports on mapping in other dragon lizards that the bearded dragon ZW pair shared common ancestry with squamate reptile chromosome 2, which now shows partial homology with the chicken Z chromosome. This supports our previous hypothesis of existence of an ancestral super-sex chromosome in amniotes.
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