Sharedifferences
The architecture of our genomes is anything but basic By Tina Hesman Saey
Whether you like it or not,
you’re a little different. If
it makes you feel any better, so is everybody else.
In fact, everybody is far more different
than anybody had imagined.
Scientists are only beginning to discover just how different humans are
from each other at the genetic level and
what those personal genetic attributes
mean for health, history and the human
evolutionary future.
It’s true that people are 99.9 percent
alike, if only minor spelling variations in
the genetic instruction book are taken
into account. In each person, about one
in every 1,000 DNA bases — the chemical
letters of the genetic alphabet — differs
from the generic human construction
and operating manual. So, on average,
one person will differ from another at
about 3 million of the 3 billion letters
in the human genome. Researchers
have recently mapped many of these
single letter variations, called single
nucleotide polymorphisms or SNPs,
looking for variants that might play a
role in complex diseases such as heart
disease, diabetes and high blood pressure (SN: 6/21/08, p. 20).
So far, SNPs have been associated with
many diseases, but SNPs can also be protective. And those little spelling differences may contain information about a
person’s geographic ancestry — just as
whether people write color or colour is
a clue about whether they hail from the
United States or Great Britain.
But SNPs aren’t the whole story of
human-to-human distinctions. Scientists now know that a different type of
variation, previously thought to be rare,
is surprisingly widespread.
New research shows that the human
genome has undergone extensive editing, much more sweeping than the minor
letter differences or spelling variations.
Entire pages may be torn from, or even
stuffed into, an individual’s genome.
Paragraphs can be duplicated multiple
times, swapped with other passages,
written backward, deleted, truncated
or otherwise altered in myriad ways.
These differences are known collectively
as structural variation, and as little as
5 percent or as much as 18 percent of the
human genome may be affected.
