What is a selection index in animal breeding?

• A. A numerical value that combines multiple traits with weights to rank animals for selection
• B. A single trait measured for performance
• C. A qualitative assessment of animal appearance
• D. A random score used for marketing

Answer: (A)

This question tests understanding of selection indexes. A selection index is a single numerical value that combines information from multiple traits into a weighted sum to rank animals for selection. Each trait is multiplied by a weight that reflects its relative importance, often tied to economic value or breeding objectives. This approach lets breeders consider overall genetic merit and balance trade-offs between traits, rather than focusing on one trait at a time. In practice, estimated breeding values for each trait feed into the index, producing a ranking that guides which animals to select. The other descriptions don’t fit: a single trait measured for performance isn’t an index; a qualitative assessment of appearance is subjective and not numeric; a random score used for marketing has no basis in genetics or economics.