Are we really 99.9 percent identical? No.

I’ve often read that we share almost the same genetic makeup with other people (and even animals). For example, an ABC News story reported:

People share 99.9 percent of the same genes…

On the other hand, I just saw this story: One man’s genes show DNA is still a mystery

Initial study of genome entrepreneur Craig Venter’s own DNA map shows 4.1 million places where his genetic code is different from the basic “reference” human genome.

This is many more than had been expected, including big differences that extend far beyond the single-letter changes that account for much of the variation seen so far.

“I think the biggest surprise is we are lot more different from one another than we thought,” Venter said in a telephone interview.

I asked Mickey for his view. Here’s what he said:

The 99.9% number that you hear about is bogus. The human genome has about 2 or 3 billion DNA base pairs. That is indeed about 99.9% similarity at the level of DNA base pairs, but if all of our DNA consisted of our ~20,000 genes and associated regulatory areas, the differences observed would average about 200 differences per gene. In practice, many genetic differences are outside coding areas, and many differences in proteins are relatively or completely silent when translated into proteins, but still the notion of sharing 99.9% of our genes is totally bogus.
Sharing 99.9% of DNA base pairs is very different from sharing 99.9% of genes. It would be interesting if the paper actually runs the numbers of the number of genes that are identical at the amino acid level (this controls for redundancies in the genetic code).

This probably comes as no surprise to most folks, who know that kids tend to look like their biological parents. But it will be a surprise to many people.

September 4, 2007

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