Genetics then and now: breeding the best and biotechnology.

In the past, domesticated animals were genetically improved by identifying meritorious individuals, mating animals displaying desired traits, continued breeding of related animals to perpetuate their superior traits and crossbreeding when inbreeding depression became evident. Today, assisted reproduction and biotechnology allow breeders to design and direct the reproductive course, disseminate desired traits and hasten genetic improvement. Generation interval can be greatly reduced by combining artificial insemination, which is the oldest and most widely used assisted reproductive technology, with the more recent techniques, such as oestrus synchronization, superovulation, ovum pick up from immature females even out of breeding season, and in vitro embryo production and transfer. Furthermore, the sex and genetic make-up of the offspring can be selected by using sex-sorted sperm for insemination, marker-assisted selection, functional deletion or addition of specific genes to the offspring's genome, or somatic cell nuclear transfer for cloning. However, the poor success rates with some of these procedures have delayed their large-scale application which, in turn, has hindered the proper evaluation of their genetic impact. The potential genetic consequences of some of these approaches merit the same degree of diligent evaluation that is currently extended to the procedures used for overcoming their 'technical' inefficiencies.