Genes, Morphogenesis, Evolution: Life and ALife Aspects

Appearance of New Genes via Duplication

A few words concerning appearance of new genes may be in place. Mostly genes originate from duplication of existing gene sequences. Any gene currently functioning in an organism will posses backward genealogy to earlier, ancestral genes. Typical story for origin of any functioning gene includes sequence duplication (i); fixation in the population, through selection or drift (ii); maintenance of function by selection (iii); and sequence evolution under mutation and selection (iiii) (Altenberg, 1995, "Genome growth and the evolution of the genotype-phenotype map", In: Evolution as a Computational Process, Wolfgang Banzhaf and Frank H. Eeckman (eds), Springer-Verlag, 205-259).

1. Thus functionally successful duplication yields apart from given gene pair O + A, their extra-copies O' + A'.
2. At first time, in evolution scale, this pair obviously is silent because of evident functional useless. As a result, in offspring genomes the O' + A' genes have freedom for accumulation of point mutations.
3. On this way, key event is appropriate mutation in coding part of O' gene (probably in the part coding DNA-binding domain) which change DNA recognition specificity. (It was apparently slight change, so that 2 or 3 nucleotide substituted in consensus.) As a result, "fortunate" O' gene will get a chance became B-gene in growing cascade. Features of mechanisms for evolutional change of DNA-protein recognition specificity is very complicated question. An idea of DNA-recognition code for transcription factors becomes attractive (Suzuki and Yagi, 1995; Choo and Klug, 1994). As first approximation we could assume such self-evident fact that the initial change of the recognition specificity is slight alteration of consensus of sites being recognised. This simple assumption agrees with scheme of one to one interaction between amino acids and basics in zinc-finger recognition of DNA (Choo and Klug, 1994). This basic assumption is sufficient to enable the following cascade down-growth via duplications. (The same is true for the A'.)
4. For the purpose of oversimplified but indirect implementation of the driving force, I assume appearance of a "virus". The virus randomly transmitted from "carriers" to health genomes. By definition, the virus successfully transmitted if host genome has in the A-gene O-binding site. I assume it inserts in the A-gene by cutting of the O-binding site and becomes silent. With predetermined probability the virus wakes up and with time gradually decrease host's reproductive potential, finally killing the host, thus eliminating affected genome from evolution.

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