Species identification in Eutheria using the SPInDel method. (a) Partial overview of the sequence alignment of mitochondrial small and large subunit ribosomal RNA genes from 237 eutherian species (obtained with the Geneious software). The plot displays the identity across all sequences for every position (high and low identity values represented by green and red bars, respectively). SPInDel conserved regions (dark areas in the alignment) are indicated by lettered arrows. (b) Sliding window analysis of nucleotide diversity (100 bp windows with a 1 bp overlap) along aligned rRNA gene sequences showing the abrupt increase and decrease in diversity values resulting from multiple alignment gaps. (c) Homo sapiens 12S rRNA secondary structure retrieved from the Comparative RNA Web Site showing the location of SPInDel conserved regions A to F. (d) Example of standard SPInDel profiles for 10 species: Homo sapiens (Hs), Mus musculus (Mm), Oryctolagus cuniculus (Oc), Equus caballus (Ec), Felis catus (Fc), Canis familiaris (Cf), Bos taurus (Bt), Ovis aries (Oa), Capra hircus (Ch) and Sus scrofa (Ss). (e) Mismatch distribution of pairwise comparisons between 237 profiles revealed that 98.9% diverge by more than four hypervariable regions. (f) Frequency of species-specific alleles (black bars on the right) and the average number of pairwise differences (blue bars on the left) in each hypervariable region.