Published online by Cambridge University Press: 23 November 2017
In classical quantitative genetic models, phenotypic value depends on genotype, but phenotypic variation among individuals of the same genotype is assumed to be the same for all genotypes. ANOVA and other statistical tests are underpinned by the assumption of a multivariate normal distribution with homogenous variances and independent normally distributed deviations. Heterogeneity of phenotypic or environmental variance has been estimated in dairy cattle (Brotherstone and Hill, 1986). Models and analyses developed by SanChristobal et al. (1998) and Sorenson and Waagepeterson (2003) provide strong evidence for litter size in pigs of heterogeneity of residual variance under genetic control. Environmental sensitivity dependent upon genotype has implications for livestock production, and may explain phenomena such as plasticity and canalisation. The aim was to calculate variability in within family variance among large half sib broiler families, in order to test for the presence of and quantify heterogeneity in residual variation amongst genotypes.
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