Another chromosome down, more to go

In the fast and furious race to decode the human genome, the smallest entrant—human chromosome 21—is second to cross the finish line. The result could eventually be a big victory for people with Down’s syndrome, scientists say.

Down’s syndrome is the most common genetic disorder; 1 in every 700 babies is born with it. It’s caused by an extra copy of chromosome 21, so the disorder is also known as trisomy 21.