In animal breeding, migration is defined as

• A. Bringing in alleles from outside the population into the herd
• B. Removing alleles from the population
• C. Random mating within the population
• D. Mutation within the population

Answer: (A)

Migration in animal breeding refers to gene flow—the movement of alleles between populations through the arrival of individuals or their gametes. Bringing in breeding stock or animals from outside the herd introduces new genetic material, which changes allele frequencies and can increase genetic diversity within the population.

This is why the statement describing bringing in alleles from outside fits best. Removing alleles from the population describes emigration or loss of alleles, not input from outside. Random mating within the population is simply panmixia, with no new alleles entering from outside. Mutation within the population adds new alleles but originates inside the population, not from outside.