There is a very good explanation of the issues surrounding selective breeding here.
Very simple to follow and very clear

http://www.beesource.com/resources/u...imal-breeding/
http://www.beesource.com/resources/u...and-variation/
http://www.beesource.com/resources/u...-bee-breeding/
http://www.beesource.com/resources/u...d-hybrid-bees/
http://www.beesource.com/resources/u...hybrid-queens/