Mr_Wilford
Member
Bernhard.visscher said:
I know of examples, just not enough to claim any are "bigger" than the others.
How about new traits being passed down through generations?
See, there's a very simple process by which new, novel genes can be added to the genome. It's called Gene Duplication
Basically, let's take one gene, called TTAC. During replication, mutational errors known as duplications can take place. So now, instead of TTAC, we have TTACTTAC. Two copies of the same gene. Usually this is harmless, as this only causes the organism to produce more of whatever the gene encodes for.
Now, lets say we get a point mutation. Now the genes are TTAGTTAC
The mutation makes the first copy broken. If this was the only copy, the organism would be harmed. But this individual has two copies, so it is not harmed.
Now, lets have a different point mutation take place: TTAATTAC
Now, with that mutation, the gene can produce functional proteins. But it has a different code, so now, we have a copy of the original gene, and a NEW variant as well. This time, it will code for a new version of the protein the organism did not posses before the duplication event. New "information", if you will.
Examples of this happening? Here's one: http://www.umich.edu/~zhanglab/clubPaper/11_02_2012.pdf
This paper describes how gene duplication can add not just one new gene variant, but over 32 novel gene variants in about 3000 generations. Here's what they did:
First the researchers got a bacteria (Salmonella enterica in this case)
with a particular gene, called HisA. This gene gave the bacteria a weak ability to survive without the amino acids histidine and tryptophan. The gene produced an enzyme that could (again, weakly) catalyze the production of both amino acids.
This was determined to be the case by placing the bacteria in a medium that lacked both histidine and tryptophan and then seeing if they were able to survive, grow, and reproduce. Which the bacteria did. Averaging about 5 hours between cell divisions. However, if they placed some histidine in the growth medium, then the cell division time dropped to 2.6 hours. If there was tryptophan and no histidine, the cells divided every 2.9 hours. If both amino acids were present, the cell doubling time dropped to 1.5 hours.
So, the strains that were in the no histidine/no tryptophan growth medium were stressed. They could survive and grow, but they weren’t good at it (as shown by the increased reproduction time).
In the case of this lab experiment, the end result was that evolution not only produced genes that were good at producing histidine and tryptophan, it also resulted in bacterial species with multiple genes.
The original gene was duplicated. That’s simply it, there was a mutation whose result was two copies of the same gene.
Now, things really get interesting. Most of the time, if you have two genes producing a catalyst, then you get more catalyst. That happened, but you also have the ability to radically mutate one of the copies of the gene without harming the organism.
And that’s the real benefit to gene duplication events. Because a mutation that would kill the bacteria could happen in one gene, but the other gene is still there, still functional and the organism lives. But again, selection takes over and there are many cases of what are called “potentiating mutations”. These mutations may be neutral or even harmful, but they are required for a future mutation that results in massive increases in functionality.
So, after 3000 generations of bacteria (that’s about two years) what were the results? Oh this is really good. You’re gonna love this.
There wasn’t one population with two genes.
There were over 32 unique populations with different types of genes. Some of them had two genes, one that did histidine production and one that did tryptophan production. Some of them had a single gene that did both really well. And there wasn’t just one version of each of the three. There were over 11 unique alleles for these genes present in the various lineages and populations.
In two years (roughly, that’s an estimate from the 3000 generations and the average generation time), there was a massive divergence in the bacterial populations. Some of the versions of the gene had a 20-fold improvement in catalytic activity.
11 new alleles. That's 11 New, Novel variants of the duplicated genes that did not exist before the experiment was run
If that isn't the production of new information by mutational mechanisms, I don't know what is. And it's a change in heritable traits over time.
