Learn More
Reptiles epitomize the variability of reproductive and sex determining modes and mechanisms among amniotes. These modes include gonochorism (separate sexes) and parthenogenesis, oviparity, viviparity, and ovoviviparity, genotypic sex determination (GSD) with male (XX/XY) and female (ZZ/ZW) heterogamety and temperature-dependent sex determination (TSD).(More)
Sex in reptiles is determined by genes on sex chromosomes or by incubation temperature. Previously these two modes were thought to be distinct, yet we show that high incubation temperatures reverse genotypic males (ZZ) to phenotypic females in a lizard with ZZ and ZW sex chromosomes. Thus, the W chromosome is not necessary for female differentiation. Sex(More)
The bearded dragon, Pogona vitticeps (Agamidae: Reptilia) is an agamid lizard endemic to Australia. Like crocodilians and many turtles, temperature-dependent sex determination (TSD) is common in agamid lizards, although many species have genotypic sex determination (GSD). P. vitticeps is reported to have GSD, but no detectable sex chromosomes. Here we used(More)
The peculiar cytology and unique evolution of sex chromosomes raise many fundamental questions. Why and how sex chromosomes evolved has been debated over a century since H.J. Muller suggested that sex chromosome pairs evolved ultimately from a pair of autosomes. This theory was adapted to explain variations in the snake ZW chromosome pair and later the(More)
Sex determination in animals is amazingly plastic. Vertebrates display contrasting strategies ranging from complete genetic control of sex (genotypic sex determination) to environmentally determined sex (for example, temperature-dependent sex determination). Phylogenetic analyses suggest frequent evolutionary transitions between genotypic and(More)
Snake sex chromosomes provided Susumo Ohno with the material on which he based his theory of how sex chromosomes differentiate from autosomal pairs. Like birds, snakes have a ZZ male/ZW female sex chromosome system, in which the snake Z is a macrochromosome much the same size as the bird Z. However, the gene content shows clearly that the snake and bird Z(More)
Reptiles show a diverse array of sex chromosomal systems but, remarkably, the Z sex chromosomes of chicken are homologous to the ZW sex chromosomes of a species of gecko, Gekko hokouensis, suggesting an ancient but common origin. This is in contrast to the ZW sex chromosomes of snakes and a species of soft-shelled turtle, Pelodiscus sinensis, which are(More)
Reptiles, as the sister group to birds and mammals, are particularly valuable for comparative genomic studies among amniotes. The Australian central bearded dragon (Pogona vitticeps) is being developed as a reptilian model for such comparisons, with whole-genome sequencing near completion. The karyotype consists of 6 pairs of macrochromosomes and 10 pairs(More)
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)(More)
Birds have a ubiquitous, female heterogametic, ZW sex chromosome system. The current model suggests that the Z chromosome and its degraded partner, the W chromosome, evolved from an ancestral pair of autosomes independently from the mammalian XY male heteromorphic sex chromosomes--which are similar in size, but not gene content (Graves, 1995; Fridolfsson et(More)