5.12 Key issues of genetic models (2024)

The phenotype is determined by the genotype and the environment.

The environment consists of any influence that occurred between conception and the moment of phenotype recording.

In breeding we are only interested in the additive genetic effect because they are transmitted to the offspring.

The variation in phenotype can be expressed as phenotypic variance.

The phenotypic variance consists of additive genetic variance and error variance.

The error variance consists of variance due to environmental effects, but it is also a waste bin containing dominance and epistatic effects, errors in the phenotypic measurements, etc.

The breeding value of the offspring consists of half the breeding value of the sire and half of the dam.

The Mendelian sampling term indicates the part of the additive genetic component in the offspring that cannot be predicted: which half of the sire was transmitted to the offspring and which half of the dam? Genomics offers the possibility to assess which alleles originate from the sire and which from the dam.

The heritability indicates what proportion of the phenotypic variance is due to additive genetic variance in the population. It is indicated with h^2.

The common environmental variance is the variance due to the fact that animals shared a common environment during (part of) their development. For example they were raised in the same litter or pen. The proportion of the phenotypic variance that is due to common environment is indicated with c².

The maternal effect is the effect of the environment created by the mother on the development of the offspring. Part of this maternal effect can be due to genetics of the mother.

An indirect genetic or social genetic effect is the effect that others have on the performance of an individual.