Evolution Can Occur Much Faster Than Previously Thought (ox.ac.uk)

An anonymous reader writes: An Oxford study on chickens discovered that evolution can make significant changes to a genome in as little as 15 years. "For a long time scientists have believed that the rate of change in the mitochondrial genome was never faster than about 2% per million years. The identification of these mutations shows that the rate of evolution in this pedigree is in fact 15 times faster." Professor Greger Larson, senior author on the study, said, "Our observations reveal that evolution is always moving quickly but we tend not to see it because we typically measure it over longer time periods."

Comments

Re:Not a huge surprise

[Michael Woodhams]

Let me see if I understand. By measuring over a long period, we're measuring the long term rate of mutation survival after applying selection pressure, and that could be noticeably different than the raw rate of mutation. Is that a correct summary?

Yes, that is correct. The technical term for 'mutation survival' is 'fixation'. A mutation is 'fixed' once the entire population carries it. It is 'extinct' (unsurprisingly) when it no longer exists in the population. When it exists in part of the population it is 'segregating'.

There are huge amounts of DNA that have no known purpose and appear to be junk. This is over 98% in humans, but varies a lot between organisms. The junkness of this is under debate. My feeling is that much of it really is junk, but some of it has a function we don't yet understand. (Also, sometimes the function is simply "we need a certain amount of space between these two bits of non-junk". This has a clear purpose, but is 'junk' in that the DNA letters don't matter.)

This particular experiment is about mitochondrial DNA which has very little 'junk', and that which it does have probably at minimum has something like 'need this amount of space' function.

Yes, scientists do like using 'junk' DNA for phylogeny (making family trees of organisms) because it is (we think) not subject to selection. On the other hand, you need to find the corresponding junk regions in all your critters and sequence them. It is easier to identify corresponding genes, and often someone else (who cared about the genes themselves) has done the sequencing work for you. Often the choice is doing phylogeny on genes using only a computer, when phylogeny on junk DNA requires samples and a molecular biology lab. Another issue is time scale: the junk DNA mutates faster, so it is good for closely related species (e.g. 'apes') but for distantly related species (e.g. 'vertebrates') you need highly conserved sequences (genes). The junk DNA will have mutated so much that it is all noise, no signal.

Is there a way to measure the mutation rates for different sites in the overall genome of a given organism, so that: (a) we can determine if some regions are actually junk because mutations to them do not affect organism fitness

Yes, if we have diverse organisms and a good alignment of their DNA, we can look for 'junk' regions by how much mutation occurs where. (Actually it tends to be the other way around - we see islands of conserved sequence, and deduce therefore that they have a function. This isn't how genes are detected, as there are more sensitive gene-specific ways of doing this.)

and (b) can distinguish between the rate of mutation and the rate of mutation survival?

Only I think by comparing mutation rates over pedigree time scales (a few generations) with mutation rates over long time scales - which is what this paper addresses.