http://www.pnas.org/content/early/2011/05/17/1013486108.full.pdf+html Assuming that goes over most peoples heads I'll explain. In Sub-Saharan Africa there is a disease called Trypanosomiasis. They have
cattle (N'Dama) that are resistant to the organisms that cause the disease (
Trypanosoma congolense), however these cattle are not very productive. They would prefer to have zebu which make better draft animals and produce more meat off of the available forage in the heat. In order to get the trait they want they took N'Dama cattle and they looked at what genes were turned on in infected cows that weren't in uninfected cows. Then they bred N'Dama with Zebu (in the normal fashion) for two generations to get a whole bunch of F2 cattle. Then they looked as the F2 cattle and discarded the ones that had the Zebu versions of the genes implicated. They seem to have stopped there, rather than continuing on with the breeding program, probably ran out of money, but it looks like we are really close to geting a breed of cattle that is both well suited to the environment and capable of handling the Tse-tse flies with out dying and with out the expense of a massively huge breeding program.
