What method of breeding is used to develop specialized "lines" of animals?

The method of breeding that is used to develop specialized "lines" of animals is inbreeding. Inbreeding involves mating closely related individuals, which can help to fix desirable traits within a population. By continuously breeding from a small gene pool, specific characteristics, such as size, color, behavior, or production traits, can be enhanced and maintained within that line of animals. This method is instrumental in creating uniformity and distinct lines that often exhibit strong traits consistently, which is valuable in livestock production for specific markets.

In contrast, crossbreeding involves mating animals from different breeds to produce offspring that potentially inherit the best characteristics from both parents. While this can lead to hybrid vigor, it may not consistently create specialized lines, as the resulting offspring can show a mix of traits.

Pure breeding refers to breeding animals of the same breed over generations, which can help maintain the characteristics of that breed but does not focus on the development of specialized lines to the same degree as inbreeding.

Multi-breeding involves crossbreeding among multiple breeds to enhance genetic diversity and can help in producing varied traits, but it does not focus on developing concentrated specialized lines in the same way that inbreeding does.

Thus, inbreeding is the most effective method