In Article <4hmte8$674 at phelix.umd.edu>, moths at Glue.umd.edu (Andrew Mitchell)
>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?
Yeah, you missed Chargaff's rule. G=C and A=T in double stranded DNA.
Although one strand could have the composition that you describe, no
double-stranded DNA could.
Department of Biological Sciences, University of Alberta
wgallin at gpu.srv.ualberta.ca