Random mutations

Hi judge,
It also explains the basis of molecular phylogenetics (and indicates a problem that can occur). You can find organisms that share a specific mutation and it is assumed to be due to common descent. However, make a bad pick of gene to analyze i.e. one that is heavily constrained, you will tend to see the same mutation appearing in non-related organisms because it either confers a specific benefit not specific to any organism or it is the only part of the gene allowed to mutate without being immediately selected out (note the mutations happen anywhere but outside of a specific sequence it might be lethal). This would tend to make a false association of the organisms sharing the mutation/allele as they do not share the mutation by common descent. Sorry to make things more complicated. Yes the mutations are random but who survives which mutation is not.