Dr Adequate
Banned
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- Aug 31, 2004
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There you go. They are starting to quantify point substitutions, insertion/deletions, recombination and other mechanisms for evolution. You have about 500,000 generations to account for the differences between the two species. You have to account for at least 35,000,000 single nucleotide changes and five million insertion deletion events...
They are seeking a mutation rate which fits the differences in the genomes of the two species. As genome sequencing improves such that generation by generation sequencing can be done quickly and cheaply, the validity of this assumption made by these authors to determine mutation rates can be tested.
Certainly.
For starters, we should be able to predict how different the genomes should be. The seven million years of evolution in each lineage represents about 350,000 generations in each (assuming 20 years per generation). How many mutations happen per generation? Estimating mutation rates is not easy (at least without assuming common descent): it is hard to find a few changed nucleotides out of 3 billion that have not changed. By studying new cases of genetic diseases, individuals whose parents' do not have the disease, however, it is possible to identify and count new mutations, at least in a small number of genes. Using this technique, it has been estimated[1] that the single-base substitution rate for humans is approximately 1.7 x 10^-8 substitutions/nucleotide/generation, that is, 17 changes per billion nucleotides. That translates into ~100 new mutations for every human birth. (17 x 3, for the 3 billion nucleotides in the genome, x 2 for the two genome copies we each carry). At that rate, in 350,000 generations a copy of the human genome should have accumulated about 18 million mutations, while the chimpanzee genome should have accumulated a similar number.
The evolutionary prediction, then, is that there should be roughly 36 million single-base differences between humans and chimpanzees. The actual number could be determined when both the chimpanzee and human genomes had been completely sequenced. When the two genomes were compared[2], thirty-five million substitutions were found, in remarkably good agreement with the evolutionary expectation. Fortuitously good agreement, in fact: the uncertainty on most of the numbers used in the estimate is large enough that it took luck to come that close.
There you go.
You can move the goalposts how you like --- we can still put the ball through them.
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