As someone who works with animal models, it is important to know your mouse strains and substrains and to make sure you are using them appropriately. I've seen experiments ruined when you get substrain contamination that convolutes the genetics that you are studying. A more devastating mistake is using a mouse on a mixed background when you thought it was pure or you get contamination from a completely different strain of mice. Often, I have seen people accidentally breed in C57BL/6N into their C57BL/6J lines and vice versa. The following paper in Genome Biology delves deeper into the differences between the two substrains. Enjoy.
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