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Memórias do Instituto Oswaldo Cruz
Fundação Oswaldo Cruz, Fiocruz
ISSN: 1678-8060
EISSN: 1678-8060
Vol. 93, No. 5, 1998, pp. 695-702
Bioline Code: oc98132
Full paper language: English
Document type: Research Article
Document available free of charge

Memórias do Instituto Oswaldo Cruz, Vol. 93, No. 5, 1998, pp. 695-702

 en Selection, Recombination and History in a Parasitic Flatworm (Echinococcus) Inferred from Nucleotide Sequences
KL Haag; AM Araújo; B Gottstein & A Zaha

Abstract

Three species of flatworms from the genus Echinococcus
(E. granulosus, E. multilocularis and E. vogeli)
and four strains of E. granulosus (cattle, horse, pig and
sheep strains) were analysed by the PCR-SSCP method followed by
sequencing, using as targets two non-coding and two coding (one
nuclear and one mitochondrial) genomic regions. The sequencing
data was used to evaluate hypothesis about the parasite breeding
system and the causes of genetic diversification. The calculated
recombination parameters suggested that cross-fertilisation was
rare in the history of the group. However, the relative rates of
substitution in the coding sequences showed that positive
selection (instead of purifying selection) drove the evolution of
an elastase and neutrophil chemotaxis inhibitor gene (AgB/1). The
phylogenetic analyses revealed several ambiguities, indicating
that the taxonomic status of the E. granulosus horse
strain should be revised.

Keywords
Echinococcus - parasites - recombination - SSCP - sequencing - phylogeny

 
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