Because of selective breeding, future generations of selectively bred plants and animals will all share very similar genes which will reduce variation. Genes and their different alleles within a population are known as its gene pool. Inbreeding can lead to a reduced gene pool, making it more difficult to produce new varieties in the future. This also makes organisms prone to certain diseases or inherited defects.
Benefits of selective breeding include:
new varieties may be economically important, by producing more or better quality food
animals can be selected that cannot cause harm, for example cattle without horns
Risks of selective breeding include:
reduced genetic variation which can lead to attack by specific insects or disease and could be extremely destructive
rare disease genes being unknowingly selected as part of a positive trait, leading to problems with specific organisms, eg a high percentage of Dalmatian dogs are deaf
the creation of physical problems in specific organisms, eg large dogs can have faulty hips due to not being formed correctly