Sliding window analysis of two cagA genes. Genes from the Venezuela and Peruvian strains (Peru2) were analyzed. Sliding window analysis of a pairwise cagA alignment was conducted using the DNASP5.0 program , using the Nei and Gojobori  method of calculating Ka/Ks. The alignment was constructed as described in Methods. A sliding window of 100 nucleotides, with a step of 10 was used. Gaps were ignored.