The apparent enhancement of CpG transversions in primate lineage is a consequence of multiple replacements

Estimating the age of single nucleotide polymorphic sites in humans

BACKGROUND

Determining the ages of polymorphic sites in human genomes needs to be carried out in a careful balance between the degree of complexity of the approach and the desired accuracy.

OBJECTIVE

We provide evidence that a simpler approach where age determination is based upon the degree to which the alternative allele is spread among the population can be competitive with more complex methods.

METHODS

The information contained in the vcf files of Phase 1 of the 1000 Genomes Project combined with the genomic sequences of seven non-human primate species was analyzed. The analyses were supplemented by a computer simulation of the mutational changes in 10,000 model chromosomes with a length of 10,000 nucleotides over a period of 16 million years. The list of the birth dates of the derived alleles of homozygous and heterozygous components of the derived alleles served as a yardstick to estimate the ages of human alternative alleles.

RESULTS

The age of the derived alleles born in Africa before the "Out of Africa" event and not brought to other continents are estimated to be 0.17 Ma, the derived alleles present simultaneously on all continents are estimated to be 1.3 Ma old and the age of alleles arising in Europe or Asia is 0.06 Ma.

CONCLUSION

Our approach functions with polymorphisms that respect the "more frequent means older" principle. However, this shortcoming only leads to disagreement with the Atlas of Variant Age in about 20% of cases.

Epigenetic Inheritance and Its Role in Evolutionary Biology: Re-Evaluation and New Perspectives

Epigenetics increasingly occupies a pivotal position in our understanding of inheritance, natural selection and, perhaps, even evolution. A survey of the PubMed database, however, reveals that the great majority (>93%) of epigenetic papers have an intra-, rather than an inter-generational focus, primarily on mechanisms and disease. Approximately ~1% of epigenetic papers even mention the nexus of epigenetics, natural selection and evolution. Yet, when environments are dynamic (e.g., climate change effects), there may be an “epigenetic advantage” to phenotypic switching by epigenetic inheritance, rather than by gene mutation. An epigenetically-inherited trait can arise simultaneously in many individuals, as opposed to a single individual with a gene mutation. Moreover, a transient epigenetically-modified phenotype can be quickly “sunsetted”, with individuals reverting to the original phenotype. Thus, epigenetic phenotype switching is dynamic and temporary and can help bridge periods of environmental stress. Epigenetic inheritance likely contributes to evolution both directly and indirectly. While there is as yet incomplete evidence of direct permanent incorporation of a complex epigenetic phenotype into the genome, doubtlessly, the presence of epigenetic markers and the phenotypes they create (which may sort quite separately from the genotype within a population) will influence natural selection and, so, drive the collective genotype of a population.