I'm stumped on a question based on dN/dS ratios in genetics. If I have two means, each with a standard error (same units), is there a simple way to approximate the standard error of the ratio?

A specific example.

dN is the average number of nucleotide substitutions per nonsynonymous site when comparing two sequences.

dS is the average number of nucleotide substitutions per synonymous site.

The dN/dS ratio is used as a way of detecting an excess of synonymous/nonsynonymous substitutions in a sequence, and thus protein sequence conservation.

The maths:

N=102.3

S = 35.7

dN=1.2953 +- 0.3006 (Standard error)

dS = 1.3986 +- 0/6759

dN/dS = 0.9262 +- ???

Would really appreciate any help, this is slowing me up!!

Thanks,

Seán