If an imported sire is evaluated in its home population, why might its breeding value be misaligned in the new population?

• A. Gene frequencies differ between populations
• B. Environment differences cause the misalignment
• C. Breeding value is universal
• D. The sire's phenotype will always match in any population

Answer: (B)

The key idea is that genotype-by-environment interaction can make a breeding value not portable across populations. A sire’s breeding value is an additive genetic merit estimate based on how its genes perform in the environment where it was evaluated. If you move that sire to a new population with different climate, nutrition, management, disease pressures, or other environmental factors, the way its genes express can change. Because performance is the result of both genetics and environment, the correlation between the sire’s estimated breeding value in the home environment and its actual merit in the new environment is not perfect, leading to a misalignment of its breeding value. Differences in gene frequencies between populations influence average performance but don’t directly make the sire’s additive value misaligned; breeding values aren’t perfectly universal across environments, and the phenotype won’t always match independent of environment.