Question: Is it possible that there are many mutations of DNA that we don't know about, as they haven't caused any diseases as of yet? Are there any mutations that have positive effects?

Lilian Hunt answered on 13 Mar 2014:

There are loads of mutations in our DNA that we haven’t found yet, I’m finding new ones every day! Not all mutations are harmful, many go unnoticed and don’t even affect us. There are also loads of diseases that we know are caused by mutations in our DNA but we haven’t found the mutations that cause them yet either!

And mutations with positive effects is exactly how things evolve 🙂 A random mutation will occur in an animal that makes it better at something in its life. Then it survives longer or breeds more and it can pass that mutation onto the next generation. The better the mutation is for the animal, the more likely it will be kept and passed onto to all its offspring. Then the offspring with the good mutation survive better and breed more too. Eventually, after many years and lots of generations of offspring, almost all of the animals in that species will have that mutation with its positive effect and the species will have evolved a bit. An example in humans is our ability to drink milk. Many East Asians are lactose intolerant – they can’t drink milk without getting a bit poorly. But a lot less Europeans are lactose intolerant because many years ago, our ancestors got a mutation that allowed us to break down milk. Now pretty much everyone in Europe can! So some mutations can have positive effects too.