Vexen Crabtree <VexenCrabtree>

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Genetic Diseases and Heterozygote Advantage: How nature hides some terrible genes behind good ones203 weeks ago
I've been writing a little on genetic diseases, here is an excerpt:

The way genetics works, some genes that have terrible effect only when inherited from both parents. This means, the gene can be successful and get passed on from generation to generation, but, it occasionally wrecks havoc on a baby or child. It is very unfortunate that this type of gene exists, but, thankfully the march of evolution means that most dysfunctional genes are eventually removed from the gene pool because they reduce the average viability of offspring. If would be so much better if evolution could see what it was doing, because there is an unfortunate twist to the way that proteins are produced from the haphazard order that genes are thrown together in. Some of these terrible diseases, which only strike families occasionally, have an advantage> when they're not showing their ugly side. This is known as "heterozygote advantage". Examples of this type of disease include sickle-cell anaemia. This disease is spread because in its hidden, harmless form it gives an advantage against malaria. Likewise, cystic fibrosis is believed to give protection against cholera, and the terrible neurodegenerative tay-sachs disease linked with protection against tuberculosis.

?Sickle cell [...] exhibits the phenomenon known as "heterozygote advantage." Heterozygotes have only one copy of a mutant gene. Since sickle cell is a recessive disorder, heterozygous people carry the sickle cell trait but do not usually get sick. It is now known that the mutation that causes sickle cell arose several thousand years ago in parts of Africa where the parasite that causes malaria had recently made its appearance. Over time, the mutation became widely disseminated in those populations, because, even though people who inherited two copies of the gene often died, those with just one copy, the heterozygotes, had significantly improved resistance to malaria.[...] Heterozygote advantage explains why some harmful mutations persist and proliferate.?
Prof. Ronald M. Green (2007)

If I was an evil architect who wanted to create a species that would suffer needlessly, then, I would design evolution in such a way that terrible diseases were hidden by genes that conferred an advantage and therefore spread well in the population. If I was a good designer, I wouldn't create genetic diseases at all. Which way does the evidence point? The existence of genetic diseases with heterozygous advantage is evidence that, if there is a creator, or a designer of evolution, such a being is either malevolent or a very poor geneticist.

Anyway, the rest of the this text is on along with much more detail on evolution in general, and some of its other quirks and inefficiencies.
 posted by Vexen Crabtree 

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