DNA might just look like squiggly rubbish. But to a scientist, DNA is like a bar code. The only people that do have the same DNA are identical twins. They look the same, and their DNA is the same. Everyone else's is unique.
Horses have DNA too.
Every living thing has DNA - everything with cells. Which means every plant, every animal, even bacteria, is made up of cells, so they've all got DNA inside them. At the moment they don't know how to change it, but they'd love to be able to. Their DNA is telling their body to make them sick. So if we can figure out what's wrong, we can change the DNA and then that disease doesn't have to exist any more.