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Sunday, July 7, 2013

genetically diverse than thought: study

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.

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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