Quantitative assessment of genomic similarity from restriction fragment patterns

A quantitative algorithm for comparing restriction fragment patterns (RFPs) was developed and used to estimate the genomic similarity of 18 isolates of pseudorabies virus of known origin. Variants of this algorithm using either untransformed or square-root-transformed differences between fragment sizes were investigated with regard to their ability to classify RFPs. Multidimensional scaling was used to represent spatially the genomic relatedness among samples, with 3 dimensions producing the most meaningful results. The square-root transformation provided more interpretable dimensions. The first dimension differentiated samples geographically, separating North American from European isolates. The second and third dimensions differentiated isolates with specific gene deletions (gE and gG, respectively) from those not having these deletions. Clusters of isolates were identified that were related either by collection from the same geographic area during a specific time period, or by laboratory intervention to create vaccines. These methods offer increased precision in the determination of genetic relatedness based on RFPs, and thus offer increased diagnostic accuracy for the determination of sources of infection.