Abstract
Among all types of mutations, single nucleotide polymorphisms are the most common type of genomic variation. In our study, we explored the counts of single nucleotide polymorphisms in consecutive exons and introns of the human genome based on the data set of 1,222 individuals of Polish origin that comprises 41,836,187 polymorphisms. Chromosomes 1 and 22 were considered to be representatives of two markedly different DNA molecules, since HSA01 represents the longest chromosome and HSA22 is one of the shortest chromosomes. Therefore, the SNP count analysis was based on 1,705,575 variants located within 6,490 genes. The distribution of single nucleotide polymorphisms among introns and exons appeared to be not only highly nonuniform but also exhibited a very consistent pattern. On HSA01, a significant excess of SNPs was observed in the first and last exons, with the first exons always containing fewer SNPs than in the last. The same pattern was also true for HSA22, except for genes represented by 7 and 8 exons. Pairwise comparisons of SNP count between introns also yielded a very consistent pattern. In HSA01 significantly higher numbers of SNPs were harboured by the first intron. On HSA22 the same pattern was observed, although it was less consistent. This observation reflects the distinct functional role of these genomic units.