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Posted by / 06-Aug-2017 21:54

Relaxed molecular clock dating

Let there be N individuals, and to keep this calculation simple, let the individuals be haploid (i.e. The probability that this new mutation will become fixed in the population is then 1/N, since each copy of the gene is as good as any other.

Every generation, each individual can have new mutations, so there are new neutral mutations will become fixed.

Instead, they represent alternative alleles that were both present as part of a polymorphism in the common ancestor.

The inclusion of differences that have not yet become fixed leads to a potentially dramatic inflation of the apparent rate of the molecular clock at very short timescales.

The molecular clock was first tested in 1962 on the haemoglobin protein variants of various animals, and is commonly used in molecular evolution to estimate times of speciation or radiation.

In particular, models that take into account rate variation across lineages have been proposed in order to obtain better estimates of divergence times.

These models are called relaxed molecular clocks and are made possible through MCMC techniques that explore a weighted range of tree topologies and simultaneously estimate parameters of the chosen substitution model.

Similarly, all vertebrate cytochrome c should be equally different from the yeast protein." For example, the difference between the cytochrome c of a carp and a frog, turtle, chicken, rabbit, and horse is a very constant 13% to 14%.

Similarly, the difference between the cytochrome c of a bacterium and yeast, wheat, moth, tuna, pigeon, and horse ranges from 64% to 69%.

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But a molecular clock does tell time -- on an epoch scale. Blair Hedges, is a tool used to calculate the timing of evolutionary events.

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