Extension, single-locus conversion and physical mapping of sex chromosome sequences identify the Z microchromosome and pseudo-autosomal region in a dragon lizard, Pogona vitticeps

Distribution of temperature-dependent sex determination (TSD) and genotypic sex determination (GSD) across the phylogeny of dragon lizards implies multiple independent origins of at least one, and probably both, modes of sex determination. Female Pogona vitticeps are the heterogametic sex, but ZZ individuals reverse to a female phenotype at high incubation temperatures. We used reiterated genome walking to extend Z and W chromosome-linked amplified fragment length polymorphism (AFLP) markers, and fluorescence in situ hybridization for physical mapping. One extended fragment hybridized to both W and Z microchromosomes, identifying the Z microchromosome for the first time, and a second hybridized to the centromere of all microchromosomes. W-linked sequences were converted to a single-locus PCR sexing assay. P. vitticeps sex chromosome sequences also shared homology with several other Australian dragons. Further physical mapping and isolation of sex-specific bacterial artificial chromosome clones will provide insight into the evolution of sex determination and sex chromosomes in GSD and TSD dragon lizards.