September 16, 2008

Genographic project paper on human mtDNA mutation rates

This is a fairly technical paper which should be of interest for those interested in uniparental markers and their age estimation.

Genetics doi: 10.1534/genetics.108.091116

Maximum Likelihood Estimation of Site-Specific Mutation Rates in Human Mitochondrial DNA from Partial Phylogenetic Classification

Saharon Rosset et al.


The mitochondrial DNA hyper-variable segment I (HVS-I) is widely used in studies of human evolutionary genetics, and therefore accurate estimates of mutation rates among nucleotide sites in this region are essential. We have developed a novel maximum-likelihood methodology for estimating site-specific mutation rates from partial phylogenetic information, such as haplogroup association. The resulting estimation problem is a generalized linear model, with a non-standard link function. We develop inference and bias correction tools for our estimates and a hypothesis testing approach for site independence. We demonstrate our methodology using 16,609 HVS-I samples from the Genographic Project. Our results suggest that mutation rates among nucleotide sites in HVS-I are highly variable. The 16,400--16,500 region exhibits significantly lower rates compared to other regions, suggesting potential functional constraints. Several loci identified in the literature as possible termination associated sequences (TAS) do not yield statistically slower rates than the rest of HVS-I, casting doubt on their functional importance. Our tests do not reject the null hypothesis of independent mutation rates among nucleotide sites, supporting the use of site-independence assumption for analyzing HVS-I. Potential extensions of our methodology include its application to estimation of mutation rates in other genetic regions, like Y-chromosome short tandem repeats.


1 comment:

McG said...

I thought that MtDNA time estimates were better understood than Y STR rates? I don't think its a novel idea to propose that different nucleotides have different rates? I am interested in what they mean by "functional constraints". I believe that Y STR mutations are constrained across the descendants from a common ancestor in some manner???