Genetic parameters for canalisation analysis of litter size and litter weight traits at birth in mice

Abstract

-The aim of this research was to explore the genetic parameters associated with environmental variability for litter size (LS), litter weight (LW) and mean individual birth weight (IW) in mice before canalisation. The analyses were conducted on an experimental mice population designed to reduce environmental variability for LS. The analysed database included 1976 records for LW and IW and 4129 records for LS. The total number of individuals included in the analysed pedigree was 3997. Heritabilities estimated for the traits under an initial exploratory approach varied from 0.099 to 0.101 for LS, from 0.112 to 0.148 for LW and from 0.028 to 0.033 for IW. The means of the posterior distribution of the heritability under a Bayesian approach were the following: 0.10 (LS), 0.13 (LW) and 0.03 (IW). In general, the heritabilities estimated under the initial exploratory approach for the environmental variability of the analysed traits were low. Genetic correlations estimated between the trait and its variability reached values of -0.929 (LS), -0.815 (LW) and 0.969 (IW). The results presented here for the first time in mice may suggest a genetic basis for variability of the evaluated traits, thus opening the possibility to be implemented in selection schemes.canalisation / variability / mice / litter size / litter weight

Genetic analysis of environmental variation

“…Some published studies using both REML and Bayesian methods on the same data have given similar estimates of genetic variance in V E (Ro¨nnega˚rd et al, 2010 ;Wolc et al, 2009) and others quite different estimates (Gutierrez et al, 2006). A more formal comparison on simulated and on real data using crossvalidation is recommended for repeated observations on the same individual or with large family groups.…”

“…Table 3 updates that of Mulder et al (2007) and shows estimates of heritability (h v 2 ), genetic coefficient of variation (GCV E ; note also that GCV 2 E s 2 A v , exp ) based on the linear model and genetic correlations (r A mv ) between the additive genetic effects for mean and V E . With one exception (Gutierrez et al, 2006, for body weight in mice), estimates of h v 2 range between 0 . 0 and 0 .…”

Genetic parameters related to environmental variability of weight traits in a selection experiment for weight gain in mice; signs of correlated canalised response

“…This Bayesian approach has previously been used in a mice population closely related to that analysed here [14]. Under this Bayesian approach two models were fitted: -The homoscedastic model (Model HO) is the classical additive genetic model, which assumes homogeneity of environmental variation:…”

“…This model has been applied to estimate genetic parameters of variability in different species and traits: litter size in sheep [30], weight at birth in pigs [1,16,17] and in rabbits [8]. Recently, Sorensen and Waagepetersen [33] described a Bayesian implementation of this model that has been applied to analyse litter size in pigs [33], adult growth in snails [27], litter size in mice [14] and uterine capacity in rabbits [19].…”

“…Some selection experiments involving livestock species have been designed and are being carried out [2] to reach this goal, but, in order to reduce the generation interval, selection experiments with laboratory mammals are necessary [14].…”