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View Full Version : H4 is it unusual or normal in mutation times and 'bushiness'?



Judith
09-21-2016, 08:25 PM
I have used the data from the supplement of Behar [1] to look at the H4 timings
From the median values the differences to the next mutation (following parent clades down) can be calculated and the mean of these mutation times is 2700 years, with an SD of 1700 years and a range of 700 to 5400 years.
This mean difference of 2700 years is uncannily similar to 100 generations if 27 years is chosen as the generation time. Any value between 25 and 30 years is credible for the generation time. Some authors state that above 1000 years the Phylogenetic rate is appropriate but in this example they are the same. Does this imply either no positive selection or purifying selection on H4? Plus is the change-over time to Phylogenetic rates further back in time? Different parts of the molecule mutate and the mutation gets fixed in the population at different rates
In biology there is a concept of purifying selection in which any mutation which is ‘poor’ is filtered out of the population in successive generations. This is the main mechanism which is proposed for the different timescales of pedigree or phylogenetic rates. In the invited review of Ho [2] considerable more detail and further references are provided on the mechanics.
My interest is H4 and particularly H4a1a1a and Loogvali stated in 2004 [3] that the H haplogroup is unusual in that it has so many branches making it unlike other European haplogroups in being so bushy. I wonder whether this is simply the coincidence of the expanding population as the Neolithic revolution progressed and was a lucky coincidence of timing for H or whether the H haplogroup really has had no purifying selection since its formation.
What does everyone else know?
1. A “Copernican” Reassessment of the Human Mitochondrial DNA Tree from its Root
Am J Hum Genet. 2012 May 04; 90(5): 936.
2. “Time-dependent rates of molecular evolution” July 2011
DOI: 10.1111/j.1365-294X.2011.05178.x http://www.robertlanfear.com/publications/assets/Ho_etal_MolEcol_2011.pdf
3 “Disuniting Uniformity etc “ Mol Biol Evol (2004) 21 (11):2012-2021.doi: 10.1093/molbev/msh209
http://mbe.oxfordjournals.org/content/21/11/2012.long