The First Black 6: C57BL/6J

As a boy, Clarence Cook Little kept mice as pets, but his hobby became serious inquiry when he began studying Mendelian inheritance of mouse coat color under William Castle at Harvard University. Wilhelm Johannsen, the Danish botanist who coined the term "gene," showed the value of inbreeding to fix characteristics, and Little applied that idea to mice. In 1909, he produced the first inbred mouse strain, DBA, from repeatedly mating brother-sister pairs. Against a "fixed" genetic background, Little sought to sort a trait far more complex than coat color: cancer susceptibility. DBA, however, showed certain frailties from inbreeding that compromised its usefulness when more resilient strains came along.