Environmental factors affecting phenotype may be divided further into known and unknown effects. We can make adjustments for known factors such as age of dam in calculating an adjusted 205-day weight. Nonadditive value is related to the hybrid vigor or heterosis effect observed from crossing unrelated lines or breeds of cattle. Because genes from the sire and dam are combined strictly by chance, the nonadditive value portion of genotype cannot be passed on from parent to offspring. The breeding value additive portion of genotype is what a parent transmits to its offspring.
Some genes have a negative effect, while others have a positive effect.
The different sizes of bricks represent the various effects that genes have. Figure 2 shows 10 gene pairs, or 20 genes, for each breeding value. The brick walls above and below the base line represent herd average. Figure 2 Classification of EBVs EBVs may be classified as either direct or maternal. The differences between direct and maternal EBVs relate to the sources of data used in their calculation.