Revision as of 13:32, 15 September 2018

Citation

Kimura, M. (1968). Evolutionary rate at the molecular level. Nature, 217(5129), 624-626.

Links

• https://www.nature.com/articles/217624a0
• https://scholar.google.com/scholar?cluster=10145631598213248063

Notes

Paragraph Four

Kimura constructs an estimate of the rate of genome-wide nucleotide substitutions based on observed amino acid differences between species.

• Average years between amino acid substitutions in 100 amino acids [math]=28\times10^6[/math] yr (today this would be "a", Latin annus, symbolizing year).
• Genome size estimate [math]=4\times10^9[/math] bp (base pairs).
• Gene size coreesponding to 100 amino acids [math]=300[/math] bp.
• Adjustment to also include an estimated additional 20% synonymous mutations that do not change the amino acid [math]1 + 0.2 = 1.2[/math]

[math]28\times10^6 \div \left( \frac{4\times10^9}{300} \right) \div 1.2 \doteqdot 1.8 {yr}[/math]

The publication (I don't know if this comes from Kimura or the typesetter) uses an obscure symbol, [math]\doteqdot[/math], for approximately equal to, [math]\approx[/math].

Kimura argues that a fixation event every 1.8 years is too high of a rate to be explained by selection. Haldane (1957) referenced here is a useful publication to understand this argument. Essentially, this requires many overlapping simultaneous selective sweeps across the genome (the time from the occurrence of a new mutation to its fixation in the population is many generations).

This appears to assume that the entire genome is protein coding DNA sequence.