Wednesday, October 26, 2011

It's not the genes that seperate us from the monkeys

The difference between humans and chimpanzees is even smaller than originally thought. New genetic research indicates that there is no difference in the genes that we possess, compared to chimps. That is peculiar, because genes function as a blueprint for all the proteins, enzymes and other building blocks that we need to form life. Instead, differences are found in the so-called 'junk DNA', parts of our genome that do not code for genes. While the name of this part of the genome hints at useless pieces of code, there is evidence that sequences in junk DNA is important for regulating gene transcription. Nevertheless, this is another striking example in how the building plans between humans and monkeys are almost identical.

According to the researchers from Georgia Tech that discovered the differences, parts of DNA in between genes affect the way they are turned on or off, possibly explaining why we differ from chimps. Elements in the junk DNA called retrotransposons seem to be the underlying factor for gene control differences between man and chimp. These elements are much like viruses: they consist of a specific piece of genetic code, and are able to jump around in the genome, while amplifying themselves. Our DNA has lots of it, but it was long thought that these jumpers did not have any function.

In their study, the scientists found that there are differences in the activity of retrotransposons between humans and chimps, and correlated their findings to differences in gene expression. Therefore, it seems that retrotransposons have a bigger role in determining our development than we previously thought. It also highlights that it is not the genes themselves, but the regulation of them that accounts for the differences between humans and chimps. While we knew it only took small changes in the genetic code to make a human instead of a monkey, it seems that the actual differences are even smaller than what we thought.

The biggest part of our genome does not code for genes. Scientists have dubbed it 'junk DNA' because it was thought that these genetic sequences had no function in the body, being remnants of billions of years of evolution, before humans were finally created. Retrotransposons, the virus-like jumping parts of the code, make up 42 percent of our genome. It is likely that we have so much of them because they were allowed to reproduce during evolution, and were consequently given a 'job' in the regulation of gene activity.

It is now known that the junk DNA possesses pieces of code that are dubbed promotors. There, the cellular machinery can be attached, to start 'reading' the gene that lies a bit further downstream. It is an example of how a piece of non-coding DNA can have an effect on genes that lie close to it.
Humans and monkeys, not so different after all.

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