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Title: GENETIC VARIANCE AND COVARIANCE PATTERNS FOR BODY WEIGHT AND ENERGY BALANCE TRAITS IN AN ADVANCED INTERCROSS POPULATION OF MICE

Author
item LEAMY, LARRY - NORTH CAROLINA STATE UNIV
item ELO, KARI - UNIV. OF NEBR-LINCOLN
item NIELSEN, MERLYN - UNIV. OF NEBR-LINCOLN
item Van Vleck, Lloyd
item POMP, DANIEL - UNIV. OF NEBR-LINCOLN

Submitted to: Genetic Selection Evolution
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/9/2004
Publication Date: 2/1/2005
Citation: Leamy, L.J., Elo, K., Nielsen, M., Van Vleck, L.D., Pomp, D. 2005. Genetic variance and covariance patterns for body weight and energy balance traits in an advanced intercross population of mice. Genetic Selection Evolution 37:151-173.

Interpretive Summary: Genes can affect more than one trait. That association is often quantified by genetic correlations. The overall polygenic genetic correlation is generally difficult to estimate with confidence. The genetic correlations between effects of individual quantitative trait loci (QTL) in two traits would be a way to partition the overall genetic correlation. A population suitable for such studies would have traits with overall heritabilities and genetic correlations which would be representative. A representative population might be constructed by crossing lines selected in different directions and then mated randomly for several generations. The logistics would be possible with mice as a model but would be prohibitive with most livestock. Analyses of such a mouse model might point to where livestock analyses should concentrate. The mouse population in this study was the result of fixing genes in lines successfully selected for high and low heat loss by full sib mating for 7 generations before crossing the lines which was followed by 11 generations of random mating. Analyses of 15 representative traits such as body weights, fatness, heat loss, feed intake, and bone and organ weights resulted in estimates of heritability as a fraction of total variation due to genetic effects that averaged 0.38 and estimates of genetic correlations that ranged from -0.71 to 0.98. Many of those estimates of genetic parameters are the first for some important complex traits and will help to discover the genetic mechanisms underlying variation due to genetic effects and how genetic effects co-vary for different traits. The conclusion was that this advanced intercross population will be ideal for discovery of QTL which regulates mammalian weight and composition traits.

Technical Abstract: Multiple-trait derivative-free restricted maximum-likelihood procedures were used to estimate heritabilities and genetic correlations for a suite of 15 characters (body weight at three different ages, four measures of adiposity, energy expenditure (measured as heat loss), energy intake, three bone characters, and three organ weights) for an advanced intercross population of over 2000 mice. This population was derived from a cross of inbred lines originally selected for high (MH) and low (ML) heat loss. Selection had resulted in a large divergence in heat loss with the MH mice losing more heat and consuming more feed, but having less body fat, than the ML mice. Estimate of heritability were significant for all measured characters (mean = 0.38), and generally were consistent with estimates derived in previous studies. Estimates of genetic correlations varied from -0.71 to +-.98 with their absolute average being 0.31. Estimates tended to be higher for characters not adjusted for weight at sacrifice. These correlations generally conformed to a priori expectations, being positive in sign for energy expenditure and consumption but negative in sign for energy expenditure and adiposity. Phenotypic correlations averaged somewhat less (absolute mean = 0.19) than genetic correlations but both sets of correlations showed high congruence in their matrix correlation (+0.87) and in the correlations of principal components. Many of the genetic parameters reported are the first of their kind for a variety of important complex phenotypes, and will aid in dissection of their genetic architectures. The results indicate that this advanced intercross population is ideal for comprehensive discovery of genes controlling regulation of mammalian body weight and composition.