Notter D R
Department of Animal and Poultry Sciences, Virginia Polytechnic Institute and State University, Blacksburg 24061-0306, USA.
J Anim Sci. 1999 Jan;77(1):61-9. doi: 10.2527/1999.77161x.
Farm animal genetic diversity is required to meet current production needs in various environments, to allow sustained genetic improvement, and to facilitate rapid adaptation to changing breeding objectives. Production efficiency in pastoral species is closely tied to the use of diverse genetic types, but greater genetic uniformity has evolved in intensively raised species. In poultry, breeding decisions are directed by a few multinational companies and involve intense selection, the use of distinct production lines, and very large populations. In dairy cattle, the Holstein breed dominates production. Intensive sire selection is leading to relatively rapid inbreeding rates and raises questions about long-term effects of genetic drift. Key questions in management of farm animal genetic diversity involve the distribution of potentially useful quantitative trait locus alleles among global livestock breeds. Experiments with tomato, maize, and mice suggest that favorable alleles can exist in otherwise lowly productive stocks; this cryptic variation may potentially contribute to future selection response. Genetic improvement under relatively intense unidirectional selection may involve both increases in the frequency of favorable additive alleles as well as the progressive breakdown of homeostatic regulatory mechanisms established under the stabilizing selection that is characteristic of natural populations. Recombination among closely linked regulatory loci and new, potentially favorable mutations are possible sources of long-term genetic variation. A greater understanding of the potential that these alternative mechanisms have for supporting long-term genetic improvement and of genetic relationships among global livestock populations are priorities for managing farm animal genetic diversity.
家畜遗传多样性对于满足当前在各种环境下的生产需求、实现持续的遗传改良以及促进对不断变化的育种目标的快速适应至关重要。草食动物的生产效率与多种遗传类型的利用密切相关，但在集约化养殖的物种中，遗传一致性却有所增加。在家禽方面，育种决策由少数跨国公司主导，涉及高强度选择、使用不同的生产线以及庞大的种群规模。在奶牛养殖中，荷斯坦品种占据主导地位。对公畜的高强度选择导致近亲繁殖率相对较快上升，并引发了关于遗传漂变长期影响的问题。家畜遗传多样性管理中的关键问题涉及潜在有用的数量性状位点等位基因在全球家畜品种间的分布。对番茄、玉米和小鼠的实验表明，有利等位基因可能存在于原本生产力较低的种群中；这种隐藏的变异可能会对未来的选择反应产生潜在贡献。在相对强烈的单向选择下的遗传改良可能既包括有利加性等位基因频率的增加，也包括在自然种群特有的稳定选择下建立的稳态调节机制的逐步瓦解。紧密连锁的调控位点之间的重组以及新的、潜在有利的突变是长期遗传变异的可能来源。更深入了解这些替代机制支持长期遗传改良的潜力以及全球家畜种群之间的遗传关系，是家畜遗传多样性管理的优先事项。
