Nc values and positive selection

MArtin John Cann mjcann at med.cornell.edu
Tue Sep 21 10:05:55 EST 1999


I am working on a cluster of genes in the fly that have very high Nc
values (59.12, 59.29, and 58.45).  A selection of "surrounding" genes in
the genome have lowered values of Nc of 34 to 49 reflecting a partial
bias in codon usage.  To what extent can I use these high values of Nc
as evidence for positive selection at the locus?  Values of pi and theta
are lowered compared to the genome average and Tajimas D statisitc is
-ve but not sufficiently so to reject the neutral mutation hypothesis.
Does this add up to reasonable evidence for positive selection?

Any advice would be greatly appreciated.

Martin Cann

mjcann at med.cornell.edu

Department of Pharmacology
Weill Medical College of Cornell University





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