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Quantitative Genetic Engineering of More Efficient Animal Production¹

U.S. Department of Agriculture, Lincoln, NE 68583-0908 and Iowa State University, Ames 50010

Abstract

Recent progress in quantitative genetics has contributed to more efficient animal production through better understanding of the underlying genetic model, genetic parameters, breeding objectives selection methods and breeding systems necessary to engineer useful genetic changes in animal performance. Biochemical genetics research affirms fewel cistron units but a higher proportion segregating than expected, with frequent recombination within units and reason for important roles of linkage and pleiotropy. Production system simulation has emphasized that relative economic importance of improved reproductive rate, growth and body composition differs greatly between animal species, production-marketing environments and breed roles. Theory, simulation and selection experiments with laboratory and domestic species have demonstrated: 1) the large effective number of genes controlling quantitative traits; 2) importance of adverse pleiotropic or epistatic effects on reproductive fitness from extreme selection for metric traits, suggesting overdominance for combined natural and imposed selection in semi-plateaued populations and across varied environments; 3) potential loss in response with relaxed selection from either adverse maternal effects or epistatic recombination and natural selection and 4) importance of large size and optimum structure of population, information on relatives, accurate economic weights and genetic parameters to maximize response and minimize sampling error. Breed evaluation and crossbreeding theory, simulation and experiments have suggested optimum use of breed and heterosis effects to maximize life-cycle efficiency under varying production-marketing systems, and suggested approaches in conservation of breed resources.

Key Words: Quantitative Genetics • Animal Production • Breeding Objectives • Genetic Engineering • Selection Response • Breed Utilization

¹ The authors are indebted to Drs. G. E. Bradford, L. V. Cundiff and D. L. Harris for critical review of the manuscript and many helpful suggestions

² Roman L. Hruska U.S. Meat Anim. Res. Center, ARS, USDA, 225 Marvel Baker Hall, Univ. of Nebraska, Lincoln.

³ Dept. of Anim. Sci., Iowa State Univ., Ames.