Hybrid vigor occurs most clearly when crossing which types?

• A. Same breed across generations
• B. Different breeds
• C. Affects only males
• D. Is achieved through cloning

Answer: (B)

Hybrid vigor, or heterosis, occurs when the genetic diversity from two different breeds is combined in the offspring. Crossing different breeds brings together distinct sets of alleles, increasing heterozygosity and allowing interactions among alleles that boost performance. This often shows up as faster growth, better fertility, stronger disease resistance, and overall vigor in the first generation. Crossing within the same breed across generations keeps the gene pools similar, so the extra heterozygosity—and thus the vigor—diminishes. This phenomenon isn’t about male-only effects, and cloning doesn’t create new allele combinations, so it doesn’t produce hybrid vigor.