Detecting Laterally Transferred Genes

Methods for identifying alien genes in genomes fall into two general classes. Phylogenetic methods examine the distribution of a gene’s homologues among genomes to find those with relationships not consistent with vertical inheritance. These approaches include identifying orphan genes which lack homologues in closely related genomes and genes with unduly high levels of similarity to genes in otherwise unrelated genomes. Rigorous statistical tests are available to place confidence intervals for predicted alien genes. Parametric methods examine the compositional properties of genes within a genome to find those with atypical properties, likely indicating the directional mutational pressures of a donor genome. These methods may compare the properties of genes to genomic averages, properties of genes to each other, or properties of large, multigene regions of the chromosome. Here, we discuss the strengths and weaknesses of each approach.