Basic features of barcodes. (a) Barcode distance distribution among chromosomes from the same organisms, across all prokaryotic and eukaryotic chromosomal genomes. The x-axis is the barcode distance and the y-axis is the frequency of chromosome pairs of the same organism having a particular barcode distance. (b) Genome barcode distances versus sequence similarities among the corresponding 16S rRNAs (based on the multiple sequence alignment given in DeSantis TZ et al. ). The y-axis represents the barcode distance, and the x-axis is the sequence identity axis between two 16S rRNAs grouped into nine bins, where the sequence identity is calculated as the average sequence identity over all 16S pairs in each bin.