Selective breeding can be seen as a way of breeding out unwanted alleles from a population, restricting genetic variation. Some people see this as an advantage as the unwanted allele is no longer present; however the disadvantage of this is the reduction of genetic diversity. Breeding animals and plants to have desired traits will benefit the plant/animal in their current environment. However breeding for their desired traits runs the risk of losing other genetic characteristics from the gene pool of the population which is an irreversible effect of selective breeding.
Another disadvantage/advantage of selective breeding is in-breeding depression. In-breeding depression is when an undesirable gene is phased out in the selectively breed organism due to the exclusivity of the desired gene. This can be an advantage for the population as this gene is no longer present however the reverse can also
References: [1]http://www.direwolfproject.com/selective-breeding.html [2]https://docs.google.com/viewer?a=v&q=cache:frQa3g2twcQJ:www.ksw.org.uk/files/biology_l6/disadvantages%2520of%2520selective%2520breeding.doc+&hl=en&gl=ie&pid=bl&srcid=ADGEESibzs26SXItEJclUK65WKY9RedpG20okOBv4kNKWNDv1C6iTxiHorxJy4XtEH58LAbHznb1wmaR02yi8LsFSXWTzc3nP3wO1Q9hNFxHz5_RbhMEcaMu0uzPpU-wboCsQ5_ZA86A&sig=AHIEtbT3I3PSNu8Ycw3tFc1GSpSe5kgm6g [3] http://bigcatrescue.org/abuse-issues/issues/white-tigers/ [4]http://images.mediastorehouse.net/172/644697_450_450_0_0_fit_0_cc88090c6bacd2f5bae4070641cdeeba.jpg