Down’s syndrome — also known as trisomy 21 — is a genetic disorder caused by an additional third chromosome 21. Although this genetic abnormality is found in one out of 700 births, only 20% of fetuses with trisomy 21 reach full term. But how do they manage to survive the first trimester of pregnancy despite this serious handicap? Researchers have found that children born with Down syndrome have an excellent genome in many ways — better, in fact, than the average genome of people without the genetic abnormality.