Re: Point mutations

Anders Sandberg (
27 Aug 1998 19:37:49 +0200

Damien Broderick <> writes:

> Everyone knows that DNA is prey to mutations, most of them quickly edited
> out by vigilant repair mechanisms, most of the rest neutral or bad news,
> only a few improving the genes they happen to occur within. But by what
> chemical pathway do those mutations come about? I'd always assumed that
> most of them involved gross *deletions* of one or more nucleotide bases,
> the implication being that the least dangerous deletion would knock out
> three adjacent bases in one go (otherwise *all* the subsequent three-letter
> codons are fouled). However, many mutations occur at a single point. The
> classic instance is the change creating sickle cell anaemia, in which
> position 6 in the 146 amino acid chain has valine instead of glutamic acid.
> Presumably this means that an adenine has been changed into a uracil (or,
> in the DNA chain, into a thymine).
> But how the hell does the equivalent of a random impact do that?

Radiation or free radicals mess up single nucleotides, changing them into other molecules, but I think the major contribution is errors in replication. If a single base is damaged (or just unlucky), the enzyme doing the replication might make a wild guess and insert a random nucleotide in the copy.

Just a guess from a computer scientists playing molecular biologist :-)

(But I do run Avida, an artificial life program, in another window)

Anders Sandberg                                      Towards Ascension!                  
GCS/M/S/O d++ -p+ c++++ !l u+ e++ m++ s+/+ n--- h+/* f+ g+ w++ t+ r+ !y