As we are all aware, base composition biases can seriously affect
phylogenetic analyses of DNA sequence data. I have seen many papers in
which such biases are assessed by examining the G+C content of
sequences. If this value is approximately 50% then authors conclude
there is no base composition bias. However, that 50% G+C could break
down further into 45% G, 5% C, 10% A and 40% T - extreme composition
bias. So why the fixation with G+C content? Is it simply a hangover
from the days before DNA sequencing, or did I miss something?