Some hints on open reading frame statistics - How ORF length depends on selection

Coding sequences of DNA generate Open Reading Frames (ORFs) inside them wit h much higher frequency than random DNA sequences do, especially in the ant isense strand. This is a specific feature of the genetic code. Since coding sequences are selected for their length, the generated ORFs are indirect r esults of this selection and their length is also influenced by selection. That is why ORFs found in any genome, even much longer ones than those spon taneously generated in random DNA sequences, should be considered as two di fferent sets of ORFs: The first one coding for proteins, the second one gen erated by the coding ORFs. Even intergenic sequences possess greater capaci ty for generating ORFs than random DNA sequences of the same nucleotide com position, which seems to be a premise that intergenic sequences were genera ted from coding sequences by recombinational mechanisms.