Nature Goes Bucknutty for Copy Number Polymorphism

There's an old paradigm in human population genetics that we each differ from each other by less than one percent at the DNA sequence level. While that may be true for our DNA sequences, recent work indicates that there's also quite a bit of variation amongst individuals in the actual content of their genomes. Such variation is known as copy number variation (CNV) or copy number polymorphism (CNP). What it means is that some people may have one copy of a genomic region, other may have two, and even others may have none.

Nature thinks this research on CNV is quite important, as there are five recent articles in Nature journals on this topic:

• An article in Nature by Redon et al (a collaboration between Stephen Scherer's group and Matthew Hurles's group) reporting a map of CNV in human populations based on 270 individuals. The found 1,447 regions that varied in copy number (CNVRs) which make up 360 megabases or 12% of the human genome. Many of these regions contain functional genes, which has implications for evolution and disease.

• Nature has also published a news item on this research.

• And Nature has a News and Views article on this research.

• And Nature has a Key Contributors piece on how some of the research was carried out.

• Not to be left out, Nature Genetics will be publishing an article that compares the two human genome project sequences (that of Celera and the one from the public project). The comparisons are used to identify structural differences between the two sequences, such as CNVs, inversions, insertions, and deletions.

While DNA sequence differences or single nucleotide polymorphisms (SNPs) may explain some of the variation within populations and differences between them, structural variations are responsible for a great deal of the phenotypic polymorphism in human populations. And while some reports are selling this research as revolutionary and groundbreaking (the one I linked to isn't that bad), keep in mind what Susumo Ohno wrote in 1970:

Had evolution been entirely dependent on natural selection, from a bacterium only numerous forms of bacteria would have emerged. The creation of metazoans, vertebrates and finally mammals from unicellular organisms would have been quite impossible, for such big leaps in evolution required the creation of new gene loci with previous nonexistent functions.

Any good evolutionary biologist realizes that all differences between taxa were, at some point, polymorphism within populations. The reason these recent papers are important is not because they shift paradigms, but because they represent technological achievements. It's because of our new-found sequencing and computing powers, along with dedicated lab work, that we can study this important feature of genome evolution at a population genetic level.

But these catalogues of structural polymorphisms are only the first step in understanding the how CNV affects evolution. Many more projects need to be completed to determine the phenotypic affects important CNPs (such as effects of a polymorphic inversion on fecundity). Some of these may represent disease loci. Others will play a role in differences between individuals. And some may even explain differences between human populations.