#pseudogene

Using pseudogene expression profiles to classify tumours & predict cancer prognosis.

Pseudogenes are genes that have accumulated so many mutations that they can't code for proteins any more.

(Short URL for linking: http://goo.gl/uzEqm )

The human genome has around 3 billion base pairs of which about 23,000 are used to code for the proteins. The rest, well, a lot of them are non-coding. One of the reasons is pseudogenes. These are genes that are basically broken as a result of a mutation.

The human genome has rather a lot of them. Zhu et al. (2007) [1] identify around 72 human pseudogenes. 27 of these are olfactory related. (We still have lots of olfactory receptors but can't use them as a result of these pseudogenes).

35 pseudogenes have been confirmed as definite human losses. This includes the Gulonolactane (L-) oxidase gene or GULO pseudogene. What this means is that unlike most other mammals (there are some exceptions, which we'll go into a bit later) is that we can't synthesise Vitamin C. We need to compensate for that with our diet, otherwise we get scurvy and die.

Now, the very interesting thing about the GULO pseudogene is that it's a smoking gun for human evolution. The reason is the exact same GULO pseudogene is also found in chimps (& other great apes). This particular mutation is only found in one cluster of animals.

What makes it a smoking gun, is that the odds of the exact same mutation (leading to the GULO pseudogene) happening independently in several species is astronomically unlikely. There are 3 bn  base pairs in the human genome. And if it was random, it would be appearing all over the mammal world, and not just a branch of primates. So this pseudogene establishes we have a common ancestor with chimps, gorillas and orangutans.

Now, some creationists try to point out that guinea pigs also have a GULO pseudogene. The problem here is simply it's a different mutation [2]. It's not the same mutation. (As an aside, there are many other pseudogenes shared by primates that are unique, so it's not all dependent on this GULO pseudogene).

The more obvious reason is there is no creationist explanation for this pseudogene. What possible reason is there to destroy our ability to synthesise Vitamin C? The actual consequence of this, if we don't have Vitamin C in our diet, we'll get scurvy and die. It's pretty hard seeing how this is a symptom of the intelligent design of a loving, benevolent God.

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[1] Zhu, J., Sanborn, Z., Diekhans, M., Lowe, C.B., Pringle, T.H. & Haussler, D. (2007). Comparative Genomics Search for Loss of Long-Eastablished Genes on the Human Lineage. PLoS Computational Biology, 3(12): 2498-2509.