30 June 2010

Yet Another Source of Human Genetic Variability

The genetic difference between individuals and between groups of related individuals, just keeps getting larger. Wikipedia lists 7 types of genetic variation, but of course there are more. Probably many more.

The latest type of genetic variation to be acknowledged comes as a startling revelation that roughly half of the human genome is made up of "transposons", or jumping genes.
Transposons, or "jumping genes," make up roughly half of the human genome. Geneticists previously estimated that they replicate and insert themselves into new locations roughly one in every 20 live births.
New results suggest that every newborn is likely to have a new transposon somewhere in his or her genome.

...Transposons resemble e-mail spam: short repeated sequences that have no obvious function other than making more of themselves. The full name for the type of transposon that is most abundant in the human genome is retrotransposon.

The "retro" term comes from how they replicate: first, the DNA is transcribed into RNA, and the RNA is reverse-transcribed into DNA again. This process normally only happens during very early in development, when the cells that will become eggs and sperm have not turned down a separate path of differentiation.

...While working in Devine's lab as a graduate student, first author Rebecca Iskow, Ph.D. devised a technique for "amplifying" the stretches of individual genomes that border transposons and reading thousands of the junctions with advanced sequencing techniques, then comparing them to the reference human genome.

"The basic problem was that a new insertion can be anywhere within three billion base pairs – how do you find it compared to all the other ones?" Devine says.

Ninety-seven percent of genomes the team surveyed had at least one rare insertion of the L1 variety of transposon that was present in only a single human in the study, and some genomes had several. Since the study surveyed 76 genomes, "rare" insertions could still be shared by large groups consisting of thousands of people. Rare insertions corresponded to the most recent transposons, which are less likely to have their jumping abilities impaired by other types of mutations.

Devine's team also showed that transposons frequently jump to new locations during the process of tumor formation. Surveying 20 lung tumors and comparing their genomes against the normal tissues they came from, the team found that six tumors had new transposons insertions that were not present in the normal adjacent tissues.

"This indicates that transposons are jumping in tumors and are generating a new kind of genomic instability," Devine says.

Transposons can inactivate tumor suppressor genes and can facilitate rearrangements that involve large stretches of chromosomes. Geneticists have already identified many transposons that interrupt genes and cause human diseases, including neurofibromatosis, hemophilia and breast cancer.

...The research was initiated at Emory University School of Medicine, where Devine was in the Department of Biochemistry. Iskow, (now a postdoctoral fellow at Brigham & Women's Hospital in Boston) was a graduate student at Emory. The findings were published in the June 25, 2010 issue of Cell. Two other papers on human transposons appear in the same issue of Cell. _ScientificComputing

More at Eurekalert.

Wikipedia lists these forms of human genetic variation:
2 Measures of variation
The transposon variation would need to be added to the list, perhaps at this year's meeting of the Human Genome Variation Society in November.

There is a reason why clans and tribes spring up so easily, and can maintain their identities for such long periods of time. Behaviour arises to a large extent from the genes. It is easier to understand -- and therefore trust -- someone who may tend to act and react in similar ways to oneself. Such tribal societies tend to marry and keep the wealth within the tribe.

Multicultural countries such as the US are attempting to accomplish on a national scale what has generally only been successful in large polyglot trading centers and imperial capitals, in the past. The low-trust interfaces found within ethnic, cultural, and religious heterogeneity can lead to higher rates of crime and vandalism.

Leftist postmodern multiculturalists tend to take exactly the wrong approach in this situation, by accentuating the differences in cultures and religions -- and trying to mould the law around these differences. In fact the opposite should be done. Each culture and / or religion must be forced to adhere to the same set of laws if a multicultural society is to be successful. That is one reason that Kagan and Sotomayor were such abysmally bad choices -- reflecting badly upon Obama's judgment. Both Kagan and Sotomayor are likely to pursue the leftist postmodern multiculturalist approach, which will result in deeper societal schisms, reduced trust, and increased violence.


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Anonymous Anonymous said...

Yes, marrying your cousin these days seems the best thing to do, especially if the "outside world" is full of morons. The Royals, Rothchilds, and other powerful families seem to keep the wealth and power within the tribe, and whether it's via 1rst, 2nd, or 3rd cousins, or some other relation through marriage or contacts it doesn't matter. Like chooses like.

Wednesday, 30 June, 2010  
Blogger Unknown said...

You misunderstood the Wikipedia list and you have equated measures of variation with forms of variation. For instance Haplotypes are a way of detecting certain common single nucleotide polymorphisms.

This is mostly a comment about technical accuracy. I don't think it invalidates your point that Geneticists are finding evidence of new kinds of human genetic variation and that a surprising amount of this correlates with traditional ethnic/racial groupings.

An example that amazed me is the gene difference in two genes, ASPM and Microcephalin found in speakers of tonal languages. Mandarin isn't just difficult for Indo-European speakers to learn, you probably lack the genetic basis to pronounce it properly. Now there's a barrier to trust: You can't really learn to speak my language.

Wednesday, 30 June, 2010  
Blogger al fin said...

Nathan: Interesting point. But I am not promoting a return to tribalism, but rather a greater awareness of how our genes influence our behaviours and our predispositions.

Tim: Thanks for pointing out the mismatch between my short description and the Wikipedia list.

In reality, the true list of types of genetic variability has not been written yet -- it is in the earliest stages of being written.

Wednesday, 30 June, 2010  

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