Viruses in the genes

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THERE was a recent article in NewScientist suggesting that viruses are the unsung heroes of evolution. Whilst that is somewhat of a sensationalist position, there is a great degree of truth in it. Many anti-evolutionists seem convinced that it is mathematically impossible that genetic variation and mutation can be a sufficient substrate upon which natural selection can act.

What they forget is that whilst a mathematical proof is always the truth, it is a truth that is dependent upon whether the mathematical model accurately reflects the physical problem. Mathematics is limited to the validity of the assumptions that underpin the statement of the problem, thus in the fixing of certain variables it’s important to distinguish between getting the maths right and getting the problem right.

The variation seen in a species, upon which natural selection can act given circumstances that favour one variation over another, is encoded by alleles; this is the name given to different “versions” of the same gene, thus for eye colour, different alleles may be: brown, blue, green etc. Some alleles are dominant, some are recessive; the dominant ones win and get used, the recessive ones lose  and don’t get used. The dominant and recessive alleles are both part of your genetic make up, and this is called your genotype. The dominant alleles result in a physical attributes in the organism, such as brown eyes, and these physical attributes are known as the phenotype.

It is true to say that whilst all phenotype is derived from the genotype, not all genotype results in phenotype. Dominant traits, because they are aspects of the genotype that are reflected in the phenotype, are traits that can be acted upon by natural selection; however recessive traits are effectively hidden from natural selection unless the DNA that codes for the recessive alleles is physically linked to a piece of DNA that results in some other dominant trait that can be selected for or against. This recessivity maintains a store of genetic diversity.
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