Diapositiva 1

• Widely used method to detect adaptive evolution accelerated rate of d N /d s
– d N = nonsynonymous (protein changing) substitutions rates
– d S = synonymous substitutions rates
d N
ω = dS
ω < 1 → Nonsynonymous mutations are slightly deleterious
ω = 1 → Amino acid changes selectively neutral
ω > 1 → Amino acid changes selectively advantageous
Statistical Methods to Detect Positive Selection
Test whether dN is significantly higher than dS .
Approximate methods
→ Normal approximation applied to dN-dS .
ML method
→ Likelihood-ratio test.
3a: test Z
3b: confronto modelli con un likelihood ratio test
(modello zero:=1)