Breed

• A breed is a group of animals of a certain species that through generations of selective breeding has become uniform in performance, appearance, and selection history.
• A species is the largest group of animals that are capable of interbreeding and producing fertile offspring.

Animal breeding in the 20th century

• The statistician R. A. Fisher (1890 – 1962) showed that the diversity of expression of a trait could depend on the involvement of a large number of so-called Mendelian factors (genes).
• He published a lot related to statistics and animal breeding, but his keynote paper came out in 1918. Fisher, together with Sewall Wright (1889 – 1988) and J.B.S. Haldane, were the founders of theoretical population genetics.
• Thomas Hunt Morgan (1866-1945) and coworkers connected the chromosome theory of inheritance to the work by Mendel and created a theory where the chromosomes of cells were believed to carry the actual hereditary material.