Selective breeding is the process of choosing a breeding stock of an animal based on specific traits that a breeder wants to reproduce in the offspring. There are two types of selective breeding or artificial selection.
Selective breeding may involve the traditional breeder's approach, which involves breeders examining the chosen trait that they want to move on to their offspring and selecting breeds that exhibit a higher amount or extreme values of that trait.
The second type of selective breeding is known as controlled natural selection. In controlled natural selection, the breeder doesn't choose which individuals reproduce but instead put the animals or plants in a controlled environment and allow them to breed more naturally.
A third approach, known as selection experiments, is conducted to determine how strong natural selection is in the wild, but this is used purely for observation and not for experimentation.
There are many reasons for selective breeding. For example, according to HowStuffWorks.com, Allerca used selective breeding to create hypoallergenic cats. What the company did was mate the animals who only possessed the traits that they found desirable for offspring. By using the selective breeding mating process, not only did Allerca create cats with specific desired traits but also they made cats that had no undesirable traits.