  Background. The large-scale pattern of distribution of genes on the
chromosomes in the known animal genomes is not well characterized. We
hypothesized that individual genes will be distributed on chromosomes in a
mathematically ordered manner across the animal kingdom. Results. Twenty-one
animal genomes reported in the NCBI database were examined. Numerically, there
was a trend towards increasing overall gene content with increasing size of the
genome as reflected by the chromosomal complement. Gene frequency on individual
chromosomes in each animal genome was analyzed and demonstrated uniformity of
proportions within each animal with respect to both average gene frequency on
individual chromosomes and gene distribution across the unique genomes.
Further, average gene distribution across animal species followed a
relationship whereby it was, approximately, inversely proportional to the
square root of the number of chromosomes in the unique animal genomes,
consistent with the notion that there is an ordered increase in gene dispersion
as the complexity of the genome increased. To further corroborate these
findings a derived measure, termed gene spacing on chromosomes correlated with
gene frequency and gene distribution. Conclusion. As animal species have
evolved, the distribution of their genes on individual chromosomes and within
their genomes, when viewed on a large scale is not random, but follows a
mathematically ordered process, such that as the complexity of the organism
increases, the genes become less densely distributed on the chromosomes and
more dispersed across the genome.
