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Ever-Young Sex Chromosomes in European Tree Frogs

Figure 1

Expected gene genealogies under different evolutionary scenarios.

The focal gene is localized either on an autosome (green) or on a sex chromosome (red) in H. arborea (Ha), H. intermedia (Hi), or H. molleri (Hm). Arrows indicate turnovers in sex-determination systems. (a) Reference genealogy for an autosomal or mitochondrial marker. (b) In H. arborea, the marker lies on a proto sex chromosome recently derived from an autosome. Sex linkage is restricted to H. arborea, and genealogy conforms to species genealogy. (c) The marker is on ancestral sex chromosomes and thus sex-linked in all three species, but its genealogy still conforms to species genealogy due to occasional X-Y recombination. (d) The marker is on ancestral sex chromosomes and thus sex-linked in all three species, but due to absence of X-Y recombination, alleles cluster according to gametologs, not species. Within gametologs, gene genealogy conforms to species genealogy. (e) In H. arborea, the marker lies on a proto sex chromosome recently derived from an ancestral sex chromosome (dashed arrow), such that HaY clusters with the ancestral HaX. The marker is sex linked in all three species, but in the sister group of H. arborea, alleles cluster according to gametolog, not species. Note that a similar genealogy would result from local gene conversion (see Figure 1 in [35]).

Figure 1

doi: https://doi.org/10.1371/journal.pbio.1001062.g001