This article is from the WSSF 2012 AFRMA Rat & Mouse Tales news-magazine.

By Karen Robbins

The photo above shows the size difference between a full grown male rat vs. a full grown large male show mouse. It also shows how the Russian Blue rat color is the same as the Blue mouse color. You can read more about the blue gene in rats, a.k.a. Russian Blue, in these research articles:

1. An independent recurrence of the blue mutation in the Norway rat and a blue-black mosaic. Curtis, M. R.; Dunning, W. F. Journal of Heredity, 1940 Vol. 31 pp. 219–222.
2. Shorter Articles and Discussion, Linkage Studies in the Rat. E. Roberts and J. H. Quisenberry. The American Naturalist, Vol. 70, No. 729, Jul.–Aug. 1936, pp. 395–399.
3. And on the difference between the dilute (d) and leaden (ln) gene in mice in the book The Coat Colors of Mice

Russian Blue Self Standard rat and Blue Self Standard mouse (mouse is leaden gene ln, mouse dd and ln look identical), both owned and bred by Karen Robbins.