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Current mood:  geeky Category: Life
Howdy. I'm writing a blog about mutations because I have found it a common misconception that all mutations are bad. In reality, most mutations don't do anything, then there are those that do bad things, and those that do good things. The ones that do good things are the ones that will usually help that organism survive.
Genetic mutations are basically copying errors in DNA. (DNA is the stuff that controls how the organism behaves and looks.) Just like when you write out a sentence a few times, some of them are going to have one or more errors. Genetic mutations can happen when DNA is copied , when it is exposed to radiation, chemicals, or viruses. It can happen in other places too (meiosis or hypermutation), but I won't go into that here.This is one example of a copying error:I don't want to make this blog too complicated, but other types of copying errors can include addition, deletion, duplication, breakages and realignments of DNA segments, among other things.I think it's important to point out that mutations don't try to obtain what the organism 'needs' to survive. They occur randomly.In animals that are made up of more than one cell, you can get somantic mutations and germ line mutations. Germ line mutations are the ones that are passed on to an organism's offspring because they happen in sex cells, somantic mutations happen elsewhere.So the only mutations that matter to evolution are germ line mutations (the ones that occur in sex cells).A phenotype is the effect DNA and the environment has on an organism.A single germ line mutation can have a range of effects: - No change occurs in phenotype
Junk DNA is DNA that doesn't seem to do anything. Mutations in junk DNA get passed on to offspring, but as far as we know, have no obvious effect on the phenotype. - Small change occurs in phenotype
A single mutation caused this cat's ears to curl backwards slightly. - Big change occurs in phenotype
Some really important phenotypic changes, like pesticide resistance in insects are sometimes caused by single mutations. A single mutation can also have strong negative effects for the organism. Mutations that cause the death of an organism are called lethals. It doesn't get more negative than that.
Some changes are way too improbable to be caused my a mutation. Too improbable that is, because the change is so large. These guys, for example:
I've already showed some beneficial mutations (the cat ears could catch more sound, and the pesticide resitence) but here are a few more, for some of you lovely skeptics.
- Kenneth Miller (1999) described a series of experiments by Barry Hall in which he deleted an important gene in a bacterium that allowed them to use sugar as a food source. As we have seen, this can happen in nature.
- There is a bacteria that has been discovered that can digest materials found in factories that produce nylon. These are synthetic materials that have been invented by people in the 1940's. The enzymes must have arisen since the time nylon was invented. It would appear this happened by new mutations in that time period. Go here for more info.
Lactose intolerance in adult mammals (including peopls) has a clear evolutionary explanation; lactose intolerance makes it easy to wean the young. Human beings, however, have taken up the habit of eating milk products. This is something that originated in cultures that kept cattle and goats. In these cultures, lactose tolerance was favoured by natural selection and so became more widespread. In the modern world there is a strong correlation between lactose tolerance and having ancestors who lived in cultures that exploited milk as a food. It should be understood that it was a matter of chance that the lactose tolerance mutation appeared in a group where it was advantageous. It might have been established first by genetic drift within a group which then discovered that they could use milk.
It should also be pointed out that an organism with a beneficial phenotype will usually be more likely to survive into maturity (and therefore reproduce, passing on that mutated gene) than other organisms of the same species without that mutation. Eventually, the mutated gene should become abundant in the species as the organisms with the mutation will be more likely to reproduce than ones without it. And there you have it, evolution. References: Talk originsNylon bugs Examples of beneficial mutationsWiki article about mutations
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