Gene traffic mediated by transposable elements shaped the dynamic evolution of ancient sex chromosomes of varanid lizard.

Lizards usually exhibit frequent turnovers and a much greater diversity of sex determination mechanisms compared to birds and mammals, with the conserved ZW sex chromosomes of anguimorph lizards originating over 115 million years ago a seeming exception. We previously discovered in an anguimorph lizard Varanus acanthurus (Vac) whose entire chrW, but not chrZ is homologous to part of the chr2 by cytogenetic mapping, suggesting its complex history of sex chromosome evolution yet to be elucidated. To address this, we assemble a chromosome-level genome, and provide evidence that the Vac sex chromosome pair has undergone at least two times of recombination loss, producing a pattern of evolutionary strata like that of birds and mammals.

The role of unbalanced segmental duplication in sex chromosome evolution in Australian ridge-tailed goannas.

Varanids are known for conserved sex chromosomes, but there are differences in the size of the W chromosome but not in morphology among species representing varying stages of sex chromosome evolution. We tested for homology of the ZW sex chromosome system with size differences in varanids among four species from two lineages in Australia, the Odatria and the Gouldii. We found that while DNA sequences of the sex chromosomes are conserved in the species we tested, we also identified a homologous region on an enlarged autosomal microchromosome that shares sequences with the W chromosome in some isolated populations of V.

Fixed Allele Differences Associated With the Centromere Reveal Chromosome Morphology and Rearrangements in a Reptile (Varanus acanthurus BOULENGER).

Chromosome rearrangements are often implicated with genomic divergence and are proposed to be associated with species evolution. Rearrangements alter the genomic structure and interfere with homologous recombination by isolating a portion of the genome. Integration of multiplatform next-generation DNA sequencing technologies has enabled putative identification of chromosome rearrangements in many taxa; however, integrating these data sets with cytogenetics is still uncommon beyond model genetic organisms.

Widespread chromosomal rearrangements preceded genetic divergence in a monitor lizard, Varanus acanthurus (Varanidae).

Chromosomal rearrangements are often associated with local adaptation and speciation because they suppress recombination, and as a result, rearrangements have been implicated in disrupting gene flow. Although there is strong evidence to suggest that chromosome rearrangements are a factor in genetic isolation of divergent populations, the underlying mechanism remains elusive. Here, we applied an integrative cytogenetics and genomics approach testing whether chromosomal rearrangements are the initial process, or a consequence, of population divergence in the dwarf goanna, Varanus acanthurus.

Diversity of reptile sex chromosome evolution revealed by cytogenetic and linked-read sequencing.

Reptile sex determination is attracting much attention because the great diversity of sex-determination and dosage compensation mechanisms permits us to approach fundamental questions about mechanisms of sex chromosome turnover. Recent studies have made significant progress in better understanding diversity and conservation of reptile sex chromosomes, with however no reptile master sex determination genes identified. Here we describe an integrated genomics and cytogenetics pipeline, combining probes generated from the microdissected sex chromosomes with transcriptome and genome sequencing to explore the sex chromosome diversity in non-model Australian reptiles.

Gene-enriched draft genome of the cattle tick Rhipicephalus microplus: assembly by the hybrid Pacific Biosciences/Illumina approach enabled analysis of the highly repetitive genome.

The genome of the cattle tick Rhipicephalus microplus, an ectoparasite with global distribution, is estimated to be 7.1Gbp in length and consists of approximately 70% repetitive DNA. We report the draft assembly of a tick genome that utilized a hybrid sequencing and assembly approach to capture the repetitive fractions of the genome.

The Burmese python genome reveals the molecular basis for extreme adaptation in snakes.

Snakes possess many extreme morphological and physiological adaptations. Identification of the molecular basis of these traits can provide novel understanding for vertebrate biology and medicine. Here, we study snake biology using the genome sequence of the Burmese python (Python molurus bivittatus), a model of extreme physiological and metabolic adaptation.

Report from the first snake genomics and integrative biology meeting.

This report summarizes the proceedings of the 1st Snake Genomics and Integrative Biology Meeting held in Vail, CO USA, 5-8 October 2011. The meeting had over twenty registered participants, and was conducted as a single session of presentations. Goals of the meeting included coordination of genomic data collection and fostering collaborative interactions among researchers using snakes as model systems.

Sequencing the genome of the Burmese python (Python molurus bivittatus) as a model for studying extreme adaptations in snakes.

The Consortium for Snake Genomics is in the process of sequencing the genome and creating transcriptomic resources for the Burmese python. Here, we describe how this will be done, what analyses this work will include, and provide a timeline.