Which is NOT a method used in line breeding?

The correct response indicates that mating entirely different breeds is not a method used in line breeding. Line breeding is a selective breeding practice aimed at maintaining or increasing desirable traits within a specific breed by mating closely related individuals, such as siblings, cousins, or uncle-niece pairings. This method leverages genetic similarities to enhance specific characteristics while trying to minimize the dilution of these traits that occurs when introducing unrelated genetics.

On the other hand, introducing entirely different breeds leads to crossbreeding, which can result in a blend of traits from both breeds and is typically not the objective of line breeding. Line breeding focuses on reinforcing established genetic lines within a breed rather than venturing outside its genetic boundaries.