Genetic hitchhiking is thought to be an inevitable result of strong positive selection in a population. The basic idea is that if a particular gene is strongly selected for (as opposed to selected against), then the chunk of the genome that carries that gene will become very common in the population. The result is a local loss of genetic diversity: all (or nearly all) of the individuals in the population will have that same chunk of genetic information, whereas before the selection process acted, there might have been a lot of variation in that chunk throughout the population. And this means that areas of the human genome that are less variable between people are suspected sites of recent positive selection. Within that chunk, there are potentially many genes and genetic elements that became more common in the population by virtue of their placement near the gene that was actually selected for. Those other genes are the hitchhikers. And it's likely that some hitchhikers are bad news - they're harmful mutations that would normally become rare or extinct in the population, but instead have become common by hitchhiking.
In the last few years, large amounts of genetic information have become available that have enabled biologists to look for evidence of such phenomena in the human genome. Specifically, two major projects have collected genetic data for the purpose of analyzing genetic variation among humans. One project, the International HapMap Project, mapped and quantified sites in the human genome that are known to vary among humans by a single genetic letter. These sites are called single nucleotide polymorphisms, or SNPs (pronounced "snips"). The project has mapped millions of these sites in a group of 270 humans representing various lineages. Another project that has made the news recently is the 1000 Genomes Project, which also seeks to provide a picture of human genetic variation using more people (more than 1000 at present) and slightly different technology. Efforts like these have taken analysis of the human genome to a new level. No longer do we merely wonder what "the" human genome is like - we can begin to learn about how genetic differences give rise to biological differences such as susceptibility to particular diseases.
And we begin to look for evidence of positive selection in the human genome.
Read a primer on hitchhiking, then read the rest of the story about harmful mutations in the human genome, at Quintessence of Dust.How harmful mutations hitchhike in the human genome
Genetic hitchhiking is thought to be an inevitable result of strong positive selection in a population. The basic idea is that if a particular gene is strongly selected for (as opposed to selected against), then the chunk of the genome that carries that gene will become very common in the population. The result is a local loss of genetic diversity: all (or nearly all) of the individuals in the population will have that same chunk of genetic information, whereas before the selection process acted, there might have been a lot of variation in that chunk throughout the population. And this means that areas of the human genome that are less variable between people are suspected sites of recent positive selection. Within that chunk, there are potentially many genes and genetic elements that became more common in the population by virtue of their placement near the gene that was actually selected for. Those other genes are the hitchhikers. And it's likely that some hitchhikers are bad news - they're harmful mutations that would normally become rare or extinct in the population, but instead have become common by hitchhiking.
In the last few years, large amounts of genetic information have become available that have enabled biologists to look for evidence of such phenomena in the human genome. Specifically, two major projects have collected genetic data for the purpose of analyzing genetic variation among humans. One project, the International HapMap Project, mapped and quantified sites in the human genome that are known to vary among humans by a single genetic letter. These sites are called single nucleotide polymorphisms, or SNPs (pronounced "snips"). The project has mapped millions of these sites in a group of 270 humans representing various lineages. Another project that has made the news recently is the 1000 Genomes Project, which also seeks to provide a picture of human genetic variation using more people (more than 1000 at present) and slightly different technology. Efforts like these have taken analysis of the human genome to a new level. No longer do we merely wonder what "the" human genome is like - we can begin to learn about how genetic differences give rise to biological differences such as susceptibility to particular diseases.
And we begin to look for evidence of positive selection in the human genome.
Read a primer on hitchhiking, then read the rest of the story about harmful mutations in the human genome, at Quintessence of Dust.
18 Comments
Atheistoclast · 23 September 2011
DS · 23 September 2011
Right. Linkage is something that evolutionary biology isn't comfortable with. What a joker.
Ban this fool now Steve. Even the bathroom wall is too good for him.
Steve Matheson · 23 September 2011
Ban? Nah. Then the terrorists have won. But send further quote mining to the BW? Faster than a neutrino.
DS · 23 September 2011
Thanks.
ksplawn · 23 September 2011
harold · 23 September 2011
Those crazy "Darwinists". Not only are they "uncomfortable with linkage", LOL, they also deny "limits to biological change".
What a bunch of nuts. They must think that any imaginable type of life can be poofed into existence magically or something.
DS · 23 September 2011
Great reference. Thanks Steve. It shows the power of modern comparative genomics. I can only think how thrilled many classical geneticists would have been if they had lived long enough to see data like this. The paper also demonstrates how complex selection can be. Of course it has limitations, but it is important to remember the power of selection as well.
This is also a great example of another type of information that can be found in the genome, evidence of selective sweeps. Once again, it did not take any intelligence to create this information, it just takes intelligence to detect and interpret it.
Atheistoclast · 23 September 2011
DS · 23 September 2011
Atheistoclast · 23 September 2011
Henry J · 23 September 2011
Of course there are limits to what known biological processes can do, but that's not the question.
The question is whether or not known life exceeds those limits.
(Of course, if it turned out that it does, the next question would be what about processes that aren't known at present.)
Henry
DS · 23 September 2011
jlesow · 24 September 2011
The inference of common descent is largely based on the limits of known biological processes.
Genetically engineered organisms lie outside what is known to be possible without intervention.
Rolf · 24 September 2011
So evolution is not directed, has no goal? Just random and selective within natural constraints? Who'd have thought.
amphiox · 24 September 2011
It is precisely because there are limits to what known biological processes can do, and all observed life is confined within limits, that we know that life evolved through limited, unguided, imperfect biological processes, and was not created by some omnipotent and omniscient designer.
John · 2 October 2011
Atheistoclast · 11 October 2011
This comment has been moved to The Bathroom Wall.
DS · 11 October 2011