The field of genetics is relatively young. Gregor Mendel carried out work in the 19th century that still forms the basis of modern genetics, but his work was largely ignored until the late 19th/early 20th century. Coupled with Darwin's evolutionary theories, research began into the inheritance of characteristics. At the time, the field was usually called eugenics - unsurprisingly, this somewhat fell out of fashion after World War II. The discovery of DNA by Crick and Watson led to an understanding of the molecular nature of genetics, and since then the field has grown massively. Modern techniques allow for genes to be examined in great detail, altered, and even moved between different organisms. This has obvious uses for all sorts of fields, most notable agriculture and healthcare, although biotechnology is likely to become applicable to many other subjects.
At the same time, population genetics continues to examine the pressures involved in selection thus giving us a better idea of just what is going on in evolution both now and over the past couple of billion years. The breadth of genetics is quite astonishing, as is much of the knowledge that has been obtained.