EXTENSIVE DNA POLYMORPHISM WITHIN AND BETWEEN 2 STRAINS OF TRICHOSTRONGYLUS-COLUBRIFORMIS

The isolation and characterization of a library of short ( < 1 kbp) DN A probes suitable for restriction fragment length polymorphism (RFLP) analysis of Trichostrongylus colubriformis are described. More than 70 % of these probes contained repetitive DNA sequences, implying that re petitive DNA is widely dispersed in the T. colubriformis genome. Analy sis of one laboratory and one field strain for RFLPs using non-repetit ive probes showed that there is extensive genetic heterogeneity within each strain (17 of 21 probe X enzyme combinations detected multiple b ands on genomic Southern blots, consistent with the existence of multi ple alleles) and also considerable polymorphism between strains (18 of the 62 bands detected were strain specific). The laboratory strain wa s not significantly less polymorphic than the field strain, suggesting that a relatively small, restricted population size is sufficient for the maintenance of the polymorphism observed. The possible applicatio ns of these data in the epidemiology and population genetics of the pa rasite are discussed.