Under the clock dating

30 Jan

In a Bayesian framework, node dating calibrates one or several internal nodes of the tree, each with a prior distribution derived from the fossil record.While total-evidence dating uses the morphological data from the fossil record and morphological and sequence data from extant taxa together to infer the tree and divergence times.The molecular clock is a technique that uses the mutation rate of biomolecules to deduce the time in prehistory when two or more life forms diverged.The biomolecular data used for such calculations are usually nucleotide sequences for DNA or amino acid sequences for proteins.- Clock runs perfectly; case is in perfect condition, no fading and no highline scratches-even at very close inspection; often original box, packing material and documentation included.

In the resulting tree, branches associated with nodes calibrated by fossils showed more dramatic substitution rate variation than branches at nodes lacking calibration.It is sometimes called a gene clock or an evolutionary clock.The notion of the existence of a so-called "molecular clock" was first attributed to Émile Zuckerkandl and Linus Pauling who, in 1962, noticed that the number of amino acid differences in hemoglobin between different lineages changes roughly linearly with time, as estimated from fossil evidence.A birth-death process with species sampling is used to specify a prior for divergence times, which allows easy assessment of the effects of that prior on posterior time estimates.We propose a new approach for specifying calibration points on the phylogeny, which allows the use of arbitrary and flexible statistical distributions to describe uncertainties in fossil dates.