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We’re more genetically diverse than thought: study

Nov. 23, 2006
Special to World Science  

New re­search has found that at least 10 per­cent of genes in the hu­man pop­u­la­tion can vary in the num­ber of cop­ies of cer­tain DNA se­quences. 

The find­ings un­der­mine a pop­u­lar view that the DNA of any two hu­mans is 99.9 per­cent alike, re­search­ers said. That idea is wide­spread; sci­en­tists still some­times cite it as ev­i­dence that there are no sig­nif­i­cant dif­fer­ences among rac­es, al­though re­cent re­search has cast doubt on both no­tions.

Courtesy nyc.gov
The new find­ings, from ge­net­i­cist Ste­phen W. Sche­rer of the Uni­ver­si­ty of To­ron­to and its af­fi­li­a­ted Hos­p­i­tal for Sick Chil­dren, could al­so re­shape think­ing on ge­net­ic dis­eases and ev­o­lu­tion, sci­en­t­ists say.

Genes usu­al­ly oc­cur in two cop­ies, one in­her­it­ed from each pa­r­ent. Sche­rer and col­leagues found some 2,900 genes—more than 10 per­cent of those in the ge­nome—with vari­a­tions in the num­ber of cop­ies of spe­cif­ic DNA seg­ments. 

These dif­fer­ences can af­fect gene ac­tiv­i­ty and bi­o­lo­gi­cal func­tions, the group said.

To un­der­stand the im­pli­ca­tions for hu­man ev­o­lu­tion and dis­ease, Scher­er’s team com­pared DNA from 270 peo­ple of Asian, Af­ri­can, or Eu­ro­pe­an an­ces­try. The in­ves­ti­ga­tors mapped the num­ber of du­pli­cat­ed or de­let­ed genes, which they call copy num­ber vari­a­tions. They re­ported the find­ings in the Nov. 23 is­sue of the re­search jour­nal Na­ture. 

The re­search­ers searched for the vari­a­tions us­ing mi­croar­rays, a ge­nome scan­ning tech­nol­o­gy that can find changes at least 1,000 nu­cleotides, or “let­ters” of ge­net­ic code, in length. They found an av­er­age of 70 of these re­gions, av­er­ag­ing 250,000 nu­cleotides long, in each sam­ple. In all, the group iden­ti­fied 1,447 dif­fer­ent copy num­ber vari­a­tions col­lec­tive­ly cov­er­ing about 12 per­cent of the ge­nome and six to 19 per­cent of any giv­en chro­mo­some.

Not on­ly were the changes com­mon, they al­so were large, Scherer said. “We’d find mis­sing pieces of DNA, some a mil­lion or so nu­cleotides long,” he added. “We used to think that if you had big changes like this, then they must be in­volved in dis­ease. But we are show­ing that we can all have these changes.”

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New research has found that at least 10 percent of genes in the human population can vary in the number of copies of certain DNA sequences. The findings undermine a popular view that the DNA of any two humans is 99.9 percent similar, researchers said. That idea is still widespread even among scientists, who sometimes cite it as evidence that there are no significant differences among races, although recent research has cast doubt on both notions. This new findings, from geneticist Stephen W. Scherer of the Hospital for Sick Children and the University of Toronto, could also reshape thinking on genetic diseases and evolution, scientists say. Genes usually occur in two copies, one inherited from each parent. Scherer and colleagues found about 2,900 genes—more than 10 percent of those in the human genome—with variations in the number of copies of specific DNA segments. These differences can influence gene activity and ultimately an organism’s function, the group said. To understand the implications for human evolution and disease, Scherer’s team compared DNA from 270 people of Asian, African, or European ancestry. The investigators mapped the number of duplicated or deleted genes, which they call copy number variations. They reported the findings in the Nov. 23 issue of the research journal Nature. The researchers searched for the variations using microarrays, a genome scanning technology that can find changes at least 1,000 nucleotides, or “letters” of genetic code, in length. They found an average of 70 of these regions, averaging 250,000 nucleotides long, in each sample. In all, the group identified 1,447 different copy number variations collectively covering about 12 percent of the genome and six to 19 percent of any given chromosome—far more widespread than previously thought, he said. Not only were the changes common, they also were large, he added. “We’d find missing pieces of DNA, some a million or so nucleotides long,” Scherer said. “We used to think that if you had big changes like this, then they must be involved in disease. But we are showing that we can all have these changes.”