Molecular Anthropology - Causes of Errors

Causes of Errors

The molecular phylogenetics is based on quantification substitutions and then comparing sequence with other species, there are several points in the process which create errors. The first and greatest challenge is finding "anchors" that allow the research to calibrate the system. In this example, there are 10 mutations between chimp and humans, but the researcher has no known fossils that are agreeably ancestral to both but not ancestral to the next species in the tree, gorilla. However, there are fossils believed to be ancestral to Orangutans and Humans, from about 14 million years ago. So that the researcher can use Orangutan and Human comparison and comes up with a difference of 24. Using this he can estimate (24/(14*2, the "2" is for the length of the branch to Human (14my) and the branch to Orangutan (14 my) from their last common ancestor (LCA). The mutation rate at 0.857 for a stretch of sequence. Mutation rates are given, however, as rate per nucleotide(nt)-site, so if the sequence were say 100 nt in length that rate would be 0.00857/nt per million years. Ten mutations*100nt/(0.00857*2) = 5.8 million years.