Applying genetic markers in practical swine breeding

摘要

Over the past decade several papers have been published related to the benefits from the use of genetic markers in animal breeding. In many cases several assumptions were made to allow the simulation of molecular (marker-aided) breeding schemes. Sincemuch of the progress made in animal populations is centered on the selection of animals within outbred populations, the most common application of marker technologies studied has been marker-assisted selection (MAS). The first assumption in these simulations is usually the presence of a number of quantitative trait loci (QTL) that control a significant proportion of genetic variation for one or more traits of economic significance. Other assumptions usually include access to relatively well-spaced marker maps and access to large resource populations suitable for discovery of QTL. The general theory indicates that genetic markers located relatively near QTL can be effectively used to practice selection more efficiently than the reliance on trait phenotypes alone. Although some QTL can have sizable effects, e.g. the RN locus effect on meat quality in pigs (5), it is expected that the majority of QTL will have moderate to small effects on economic traits of interest. It is usually assumed that only QTLof large to moderate effect will be identified using markers and used in MAS schemes and the remainder of QTL of small effect will be lumped together as the 'polygenic component' and selected upon using traditional Best Linear Unbiased Prediction (BLUP)techniques. In addition to the assumptions above, it is also important to consider several trait parameters to accurately predict the relative value of genetic markers compared to traditional selection alone. These parameters include trait heritability,age at which phenotypes are expressed, sex-linked traits and the relative cost and difficulty of phenotyping versus genotyping. Since a few swine breeding companies are now actively pursuing molecular breeding programs, it is of interest to consider howrealistic these underlying assumptions are and to examine the benefits of genetic markers in practical swine breeding programs.