Length of introns varies from tens to tens of thousands nucleotides. The wide variety of lengths of introns and exons in genomes may be caused by evolutionary factors. To reveal these factors we applied a few techniques of factor analysis. The exon-intron structures of eukaryotes genes are quite different from each other, and studying of the evolution of such structures has no obvious attitude. Our choice was to perform statistical analysis of certain average characteristics of these structures. Comparing those chromosomal and genomic averages, we have selected an appropriate technique of clustering. This technique separates different species, grouping them according to eukaryotes taxonomy. The readers of the book need not have either advanced mathematical skills or deep knowledge of molecular biology. However, they must have a keen interest in evolution, bioinformatics or systematics.