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Parasitology. 2013 Dec;140(14):1822-30. doi: 10.1017/S0031182013001315. Epub 2013 Aug 19.

Parastrongyloides trichosuri suggests that XX/XO sex determination is ancestral in Strongyloididae (Nematoda).

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Department of Evolutionary Biology, Max Planck Institute for Developmental Biology, D-72076 Tübingen, Germany.


The parasitic roundworms Strongyloides stercoralis (in man) and Strongyloides ratti (in rats) employ environmentally controlled XX/XO sex determination with a pair of X chromosomes and two pairs of autosomes. Strongyloides papillosus (in sheep) has only two pairs of chromosomes, one of which combines the genetic material homologous to the S. ratti chromosomes X and I. This species creates males through the elimination of one copy of the portion related to the X chromosome (chromatin diminution). It is not clear which one of these two sex-determining mechanisms is ancestral. We demonstrate that Strongyloides vituli (in cattle) has two pairs of chromosomes like its very close relative S. papillosus whereas Parastrongyloides trichosuri, a closely related out-group to Strongyloides spp. in Australian brushtail possums, has three chromosome pairs and employs XX/XO sex determination. The X chromosome of P. trichosuri is homologous to the X chromosome of S. ratti. Our data strongly suggest that the last common ancestor of Strongyloides spp. and Parastrongyloides spp. had two pairs of autosomes along with two or one X chromosome in females and males, respectively. The situation with two pairs of chromosomes is likely derived and occurred through the fusion of the X chromosome with an autosome.

[Indexed for MEDLINE]

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