A statistical analysis of nucleotide sequences of introns and exons in human genes

DNA sequences of 56 human genes for which information on both exons andintrons was available were examined. The variance in G+C content amonggenes is estimated and shown to be substantial. There is a high correlationin G+C content between exons and introns within the same gene. Thedinucleotide frequencies of introns are similar to those of intergenicspacer regions and are in reasonable agreement with predictions fromsubstitution rates estimated from pseudogenes, except that the observeddeficiency of TA doublets is not predicted. Duplicated bases also show afrequency greater than the expectation under independence. There is markedvariability among genes in the frequency of the doublet CG relative to itsexpectation under independence. This variation is evolutionarily conservedand is correlated with the G+C content. Pseudogenes behave as if they arein a low -G+C, CG-deficient part of the genome, although the genes fromwhich they arose are variable in these respects.