Questions: G to A and C to T conversions, a rule ?

[Mike Zwick]

In article <zxiong.47.000BF7DF at arizvm1.ccit.arizona.edu>,
zxiong at arizvm1.ccit.arizona.edu (Zhongguo Xiong) wrote: 
> Let me try to explain it a little better. We have found 16 nucleotide 
> substitutions in about 1500 nucleotide of overlapping sequences. There are 11 
> C to T or T to C substitutions and 5 G to A or A to G substitutions. We have 
> not found any other possible substituions.
> 
> Is there a theory describing the rule  of nucleotide substitution during 
> evolution? I feel very ignorant and hope someone can give me a pointer to how 
> to explain my observation.

What you describe is the oft observed excess of transitions (A-G or C-T
substitutions) over transversions (i.e. A-T, A-C, others).  The pattern
depends upon the type of DNA sequence (coding, non-coding) and other
factors.  A good place to start in getting some background and a basic
introduction to molecular evolution is in:   Fundamentals of Molecular
Evolution by Wen-Hsiung Li and Dan Graur.



-- 
mike zwick
mezwick at ucdavis.edu
Department of Ecology and Evolution
Center for Population Biology