The First Black 6: C57BL/6J

The black 6 mouse, above, was developed around 1920 by Clarence Cook Little (1881-1971), below. Credit: COURTESY OF THE JACKSON LABORATORY ARCHIVES 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 Univer

By | January 1, 2007

<figcaption>The black 6 mouse, above, was developed around 1920 by Clarence Cook Little (1881-1971), below. Credit: COURTESY OF THE JACKSON LABORATORY ARCHIVES</figcaption>
The black 6 mouse, above, was developed around 1920 by Clarence Cook Little (1881-1971), below. Credit: COURTESY OF THE JACKSON LABORATORY ARCHIVES

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.

Sometime around 1914, Little obtained a female mouse, code numbered 57, and a male, numbered 52, which he inbred through at least twenty generations (3-4 generations a year). He named the resulting strain C57BL/6 (a J was added later to indicate the Jackson Laboratory, which Little founded in 1929).1 The upper-case C may have distinguished this black-coated mouse from the lower-case c for a recessive albino strain. The number 6 referred to one of multiple lines within the strain, among others that did not survive inbreeding pressure. Though C57BL/6J or "black six" had some inherited weaknesses, it was a good breeder, and showed delayed senescence of its hematopoietic system compared to DBA. Eventually, it became the most widely used strain of inbred mouse for the study of mammalian genetics, and it was the first nonhuman mammal to be sequenced in 2002.2

tsharrer@the-scientist.com

<figcaption> Credit: COURTESY OF THE JACKSON LABORATORY ARCHIVES</figcaption>
Credit: COURTESY OF THE JACKSON LABORATORY ARCHIVES

References

1. Strain info: http://jaxmice.jax.org/strain/000664.html 2. R.H. Waterston et al., (Mouse Genome Sequencing Consortium), "Initial sequencing and comparative analysis of the mouse genome," Nature, 420:520-62, 2002.

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