Genetic variation and the consequence in phenotype

What makes us who we are?

Popular opinion, fostered by the newspapers and television, took the view that we were determined by our genes. That is to say, everything about us was determined by our genes. Although most scientists did not believe this was not the case, it was not until the completion of the mapping of the genome that science reporters began seriously to latch on to the idea that there really is more to us than just our genes.

Steven Rose puts it this way:

"Humans are not empty organisms, free spirits constrained only by the limits of our imaginations. Nor are we reducible to "nothing but" machines for the replication of our DNA. We are rather, the product of the constant dialectic between "the biological" and "the social" through which humans have evolved, history has been made and we as individuals have been developed."

(1) Lifelines, Biology, Freedom and Determinism, copyright (c) Steven Rose 1997, Allen Lane Penguin Press, ISBN 0-713-99157-7

There are two types of variation within genes

• one sort are code variations for eye colour, skin colour and such which are normal variations within a species.
  (These are called polymorphisms = many shapes, implying that many shapes are possible within a species)
• the other sort are variations which lead to clinical conditions require medical intervention and support.
• one of the problems here is that some variations lead to clinical conditions which affect life style but not the quality of life, and do not require medical intervention.

Of special significance within each Chromosome two kinds of variation:

• STR - Short tandem repeats, These are stretches of DNA that do not code for proteins, but which comprise repeats of base pairs which at a given location differ in the number of repeats from person to person. These are used by forensic scientists to identify DNA as belonging to a particular person.

• The other variations are called SNP (Nothing to do with the Scottish National Party, but standing for Single Nucleotide Polymorphisms - these are genes in which one base varies from one group of people to another group of people. There is considerable interest in these because they may relate to susceptibility to a particular disease, or conversely to a resistance to a particular condition.