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Why look at G+C content?

Warren Gallin wgallin at gpu.srv.ualberta.ca
Thu Mar 7 21:13:23 EST 1996

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.

Warren Gallin,
Department of Biological Sciences, University of Alberta
wgallin at gpu.srv.ualberta.ca

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