How can the number of genes increase through evolution?

Question

I am aware of the basics of evolutionary theory, however I don't understand how mutations can add genes over time. Am I correct in thinking that creatures within the same species who mutate to have an additional gene in their genome would normally be infertile? Or am I misunderstanding that? Can someone explain the process of the creation of genetic material through evolution? Citation to a decent academic paper or book on the matter would be appreciated too.

Answer 1

A gene mutation is possibly a new gene. More than 99.99% of mutations are either lethal or ant-competitive, however even if the chance of a good mutation is .0000000001 % genes are changed every hour and over a 100,000 year period it is possible that some new genes provide an evolutionary advantage. In fact, without this assumption evolution would not be possible.