Pleiotropic genes

A gene that is pleiotropic is one that affects more than one expressed character.  Not only is this true but it seems that one gene can affect very widely differing characteristics.  This does not accord with the basic principles of Evolution.  How can one gene affect characteristics which have no relationship to each other?  This is what pleiotropy is really all about.

Apparently there are many pleiotropic genes; in fact the informed opinion is that there are few if any genes that are not pleiotropic (Mayr 1970).  This merely stacks the deck even more against Evolution.

Pleiotropy is invariably species-specific.  That is to say, the characteristics which any gene affects tend to be unique to one species.  In another species that same gene will have an entirely different set of effects.  This again is completely opposite to what we would expect an evolved system to produce.

For example, the mutations in one gene in the domestic chicken affect

• wing development
• hind limb digit (claw) development
• the extent of the downy cover of the skin
• the presence or absence of lungs
• air sacs
• the ureter and kidney.

Another gene in the fowl causes the formation of a crest of feathers, and causes a cerebral hernia (hole) with an upswelling in the skull to accomodate it.  It is difficult to believe that this gene has any homologue in a vertebrate lacking feathers, and yet it is involved in the development of the skull, a feature possessed by all vertebrates!

Pleiotropy also implies that apparently homologous structures are specified by different genes in different species.  In the house mouse, nearly every coat-colour gene has an effect on body size!  14 out of 17 x-ray induced eye colour mutations in the fruit-fly affected the shape of the female sex organs, a characteristic which is not logically associated with eye colour.

How does this chime in with evolution?  The simple answer is that any form or sequential evolution is ruled out.  If not, we are in the almost impossible situation of the production of homologous structures by means of totally different genes in all species.

A related, but even more important, issue is overlapping genes.  To understand this a fairly thorough knowledge of the DNA and RNA function is required, but the effects can be simply stated.  Any single 'run' of DNA was at one time thought to code for one protein.  Every three DNA subunits code for one amino acid which turns up in the final protein.  However by starting the decoding one subunit down the DNA chain an entirely different protein is produced, and by starting two down yet another one appears.

This all sounds perfectly OK, until it is appreciated that almost all proteins are very fussy as to structure, and it would be like trying to make an English sentence from a sequence of letters, from which, by moving one letter along the string, one could turn up another sentence, and, by moving down one more, a third.  Try it.  The problems of creating viable sentences in this way are massively difficult, and the difficulty is at least as great in DNA.  Nevertheless we have found many such DNA sequences.  To claim that this all arose simply by chance alone stretches credulity well beyond breaking point.

References:
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Mayr, E., (1970) 'Population, Species and Evolution' Harvard, p93