Genetic heterogeneity of residual variance in broiler chickens

Suzanne J Rowe,Ian MS White,William G Hill,Santiago Avendaño

doi:10.1186/1297-9686-38-6-617

Suzanne J Rowe, Ian MS White + Show 2 more

Open Access

https://doi.org/10.1186/1297-9686-38-6-617

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Abstract

Aims were to estimate the extent of genetic heterogeneity in environmental variance. Data comprised 99 535 records of 35-day body weights from broiler chickens reared in a controlled environment. Residual variance within dam families was estimated using ASREML, after fitting fixed effects such as genetic groups and hatches, for each of 377 genetically contemporary sires with a large number of progeny (> 100 males or females each). Residual variance was computed separately for male and female offspring, and after correction for sampling, strong evidence for heterogeneity was found, the standard deviation between sires in within variance amounting to 15–18% of its mean. Reanalysis using log-transformed data gave similar results, and elimination of 2–3% of outlier data reduced the heterogeneity but it was still over 10%. The correlation between estimates for males and females was low, however. The correlation between sire effects on progeny mean and residual variance for body weight was small and negative (-0.1). Using a data set bigger than any yet presented and on a trait measurable in both sexes, this study has shown evidence for heterogeneity in the residual variance, which could not be explained by segregation of major genes unless very few determined the trait.

Highlights

In the simplest terms, phenotypic value is the sum of the genotypic value and a residual error contributed by random environmental or other non-genetic influences, such as developmental noise
There is evidence to suggest that residual heterogeneity is under genetic control, based on analysis of data on fecundity of sheep by SanCristobal-Gaudy et al [23], who used a log linear model to test the significance of additive genetic influence on the residual variance
Progeny born in a particular hatch from a particular mating group come from contemporaneous parents and shared the same environment

Summary

Introduction

Phenotypic value is the sum of the genotypic value and a residual error contributed by random environmental or other non-genetic influences, such as developmental noise. As environmental variance cannot usually be estimated directly, but only from the variation within families, genetic and non-genetic causes are confounded. Foulley and Quaas [4] discuss the estimation of source and magnitude of effect of heterogeneous variances within linear mixed models. There is evidence to suggest that residual heterogeneity is under genetic control, based on analysis of data on fecundity of sheep by SanCristobal-Gaudy et al [23], who used a log linear model to test the significance of additive genetic influence on the residual variance. Earlier and more direct evidence for genetically structured adaptation or environmental sensitivity is found in studies of genetic assimilation [27] canalisation [18] and environmental plasticity [26]

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