Crossbreeding often results in heterosis. What does heterosis refer to in animal production?

• A. Inbreeding depression
• B. Reduced heterozygosity in offspring
• C. Environmental effects on phenotype
• D. Hybrid vigor, resulting in improved performance in offspring

Answer: (D)

Heterosis, or hybrid vigor, is the idea that crossbred offspring tend to perform better than their parents on important production traits. In animal production this often shows up as faster growth, greater size, improved feed efficiency, higher fertility, or stronger disease resistance. The boost comes from combining diverse genetics from two different populations, increasing heterozygosity and enabling favorable gene combinations to expressing more robustly.

That’s why the description “hybrid vigor, resulting in improved performance in offspring” best fits. The other ideas don’t capture the same idea: inbreeding depression is a decline in fitness from mating related animals; reduced heterozygosity describes what happens with inbreeding, not crossbreeding; environmental effects influence phenotype but heterosis is a genetic advantage from crossing diverse breeds.