Selective breeding is used to change the genetic profile of plant and animal species to either create characteristics that are required in them or to enhance the characteristics if they are already present.
Farmers regularly use plant breeding to enhance the yield of crops, make them more resistant to pests and allow their growth in unfavorable conditions. To accomplish this, different species of the same crops are studied and those that have the required characteristic are used to create offspring that may have all the required characteristics. This requires several rounds of breeding and all the resulting offspring have to be analyzed to find those that have the required characteristics. The suitable offspring are then inbred and their seed used.
An example of this is a hybrid created from two type of peas. One that is resistant to mildew but has a low yield and the other that has a high yield but is not resistant to mildew. By using the two species to create offspring, farmers have been able to create a new species that has a high yield and is resistant to mildew as well.
Selective breeding is when a breeder selects the animals or plants that will mate. Another term for this is artifical selection.
An example of selective breeding can be seen in the different dog breeds. By selecting the mating pair, dog breeders have been able to create many different breeds of dogs.