Chromosome-Specific Centromere Sequences Provide an Estimate of the Ancestral Chromosome 2 Fusion Event in Hominin Genomes

Abstract

Human chromosome 2 is a product of a telomere fusion of two ancestral chromosomes and loss/degeneration of one of the two original centromeres. Genomic signatures of this event are limited to inverted telomeric repeats at the precise site of chromosomal fusion and to the small amount of relic centromeric sequences that remain on 2q21.2. Unlike the site of fusion, which is enriched for sequences that are shared elsewhere in the human genome, the region of the nonfunctioning and degenerate ancestral centromere appears to share limited similarity with other sites in the human genome, thereby providing an opportunity to study this genomic arrangement in short, fragmented ancient DNA genomic datasets. Here, chromosome-assigned satellite DNAs are used to study shared centromere sequence organization in Denisovan and Neandertal genomes. By doing so, one is able to provide evidence for the presence of both active and degenerate centromeric satellite profiles on chromosome 2 in these archaic genomes, supporting the hypothesis that the chromosomal fusion event took place prior to our last common ancestor with Denisovan and Neandertal hominins and presenting a genomic reference for predicting karyotype in ancient genomic datasets.