Pitfalls of barcodes in the study of worldwide SARSCoV-2 variation and phylodynamics

DEAR EDITOR,Analysis of SARS-CoV-2 genome variation using a minimal number of selected informative sites conforming a genetic barcode presents several drawbacks.We show that purely mathematical procedures for site selection should be supervised by known phylogeny(i)to ensure that solid tree branches are represented instead of mutational hotspots with poor phylogeographic proprieties,and(ii)to avoid phylogenetic redundancy.We propose a procedure that prevents information redundancy in site selection by considering the cumulative informativeness of previously selected sites(as a proxy for phylogenetic-based criteria).This procedure demonstrates that,for short barcodes(e.g.,11 sites),there are thousands of informative site combinations that improve previous proposals.We also show that barcodes based on worldwide databases inevitably prioritize variants located at the basal nodes of the phylogeny,such that most representative genomes in these ancestral nodes are no longer in circulation.Consequently,coronavirus phylodynamics cannot be properly captured by universal genomic barcodes because most SARS-CoV-2 variation is generated in geographically restricted areas by the continuous introduction of domestic variants.

Biogeographical informativeness of Y-STR haplotypes

Research on biogeographical ancestry(BGA)is becoming of growing interest in forensic genetics and in the biomedical literature(1)Thus,for instance,the need to predict ethnicity of an unknown suspect based on DNA profiles found at the crime scene is of maximum interest in criminalistics[2],and several autosomal SNP panels have been designed and tested for BGA investigations[3,4].Most of these panels aim at discriminating three main continental groups(sub-Saharan Africans,Europeans,and Asians)by way of testing a number of ancestry informative markers(AIMs)that run from a few dozens to a few hundred[5](see more background in Supplementary data online).