  The problem of the directionality of genome evolution is studied from the
information-theoretic view. We propose that the function-coding information
quantity of a genome always grows in the course of evolution through sequence
duplication, expansion of code, and gene transfer between genomes. The
function-coding information quantity of a genome consists of two parts,
p-coding information quantity which encodes functional protein and n-coding
information quantity which encodes other functional elements except amino acid
sequence. The relation of the proposed law to the thermodynamic laws is
indicated. The evolutionary trends of DNA sequences revealed by bioinformatics
are investigated which afford further evidences on the evolutionary law. It is
argued that the directionality of genome evolution comes from species
competition adaptive to environment. An expression on the evolutionary rate of
genome is proposed that the rate is a function of Darwin temperature
(describing species competition) and fitness slope (describing adaptive
landscape). Finally, the problem of directly experimental test on the
evolutionary directionality is discussed briefly.
