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Natural Selection on the
Olfactory Receptor Gene
Family in Humans and
Chimpanzee
Chloe Lee
Question
Human have more than 1000 OR genes,
and about 40% have intact (non-mutated)
coding region : functional
 68 to 72% for apes
 Comparing the variations at the OR genes
with at intergenic region (a stretch of DNA
sequences located between clusters of
genes that contain few or no genes)
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Method
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OR genes were obtain from HORDE database
PCR and DNA sequencing
LOTS OF STATISTICAL data analysis
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Diversity level by Watterson’s θw,
Average number of pairwise differences in the sample
Ka/Ks: ratio of non-synonymous to synonymous
Etc
Marginal posterior distribution of the directional selection parameter
on amino acid replacement mutations
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A: Chimpanzee
B: Human
Dotted: pseudognes
straight: functional
the posterior
distributions of γ : 0.
Also 95% std dev of
pseudogene is very
similar for both
species
This data indicates
that amino acid
replacement
mutations in
pseudogenes have
little effect on fitness
Findings
Diversity pattern due to natural selection,
not demography.
 Purifying selection acting on intact OR
genes of chimpanzee
 Positive selection acting on some of intact
OR genes of human
 Most human genes are under no or little
evolutionary constraint, but may evolve
under the positive selection.
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