Genetic variation in humans greater than previously thought

Tom Spears:

New Canadian research shows that at least 10 per cent of genes in the human population can vary in the number of copies of DNA sequences they contain — challenging current thinking that the DNA of any two humans is 99.9 per cent similar.

For years, geneticists have been teaching that even people of different races are identical in all but a tiny fraction of one per cent of their DNA.

Now Stephen Scherer, a geneticist at the Hospital for Sick Children and the University of Toronto, says there are massive chunks of DNA that show up differently from one person to another, even within the same racial group.

The genes from two people make look the same, he says, except that one person may have an extra copy of a long section of DNA — like a book with one page printed twice. Some people’s DNA also has such “pages” missing completely.

Scherer and colleagues found approximately 2,900 genes — more than 10 per cent of all the genes that humans have — with variations in the number of copies of specific DNA chunks. These, he says, may make the gene function differently.

His findings are reported today in Nature, a major science journal.

His team compared DNA from 270 people with Asian, African, or European ancestry, looking for variations at least 1,000 bases (nucleotides) long. A base, or nucleotide, is the smallest piece of DNA. They found 1,447 sections capable of these huge variations, about 70 per person, on average.

"We'd find missing pieces of DNA, some a million or so nucleotides long," Scherer says in a written announcement of his findings. "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" without necessarily being sick.

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