My friend has a baby who was just born. They are worried that he doesn't have enough chromosomes, and his hand only has 1 line on it. What could it b?

Geneticist can help. Parents in consultation with the OB and peds doctors may choose to keep private what they discuss and learn. In general, if a newborn has appearance that is unusual, a test or tests will be done for chromosomes and genetic information, and, if available, a pediatric geneticist will be called. Even if the baby is given a tentative diagnosis, family and friends should wait for final test results.
See a Doctor. Your friend should have their child evaluated by a physician if they are concerned. The "one line" on the hand you speak of may be a simian crease which is actually associated with too many chromosomes; trisomy 21 or commonly known as down syndrome. There is really not enough information to make a determination, but genetic testing and other symptoms may shed some light on their concern.