The First Sexual Lineage and the Relevance of Facultative Sex |
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Authors: | Joel Dacks Andrew J Roger |
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Institution: | (1) Department of Biochemistry, Dalhousie University, Halifax, N.S., Canada, B3H 4H7, CA |
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Abstract: | Models for the origin of the sex incorporate either obligate or facultative sexual cycles. The relevance of each assumption
to the ancestral sexual population can be examined by surveying the sexual cycles of eukaryotes, and by determining the first
lineage to diverge after sexuality evolved. Two protistan groups, the parabasalids and the oxymonads, have been suggested
to be early-branching sexual lineages. A maximum-likelihood analysis of elongation factor-1α sequences shows that the parabasalids
diverged prior to the oxymonads and thus represent the earliest sexual lineage of eukaryotes. Since both of these protist
lineages and most other eukaryotes are facultatively sexual, it is likely that the common ancestor of all known eukaryotes
was facultatively sexual as well. This finding has important implications for the ``Best-Man hypothesis' and other models
for the origin of sex.
Received: 21 August 1998 / Accepted: 26 December 1998 |
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Keywords: | : Oxymonad — Parabasalid — Eukaryote phylogeny — Melosis — Origin of sex |
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