Inbred mice

At Nobel Intent, Jonathan Gitlin writes about the diversity of lab mice:

Now, scientists don't use just any mice; you couldn't trap one in your attic and then bring it to work. Instead, there are hundreds of inbred strains that are used. Creating such a strain involves mating sibling mice for at least 20 generations. By this point, almost all the genetic loci will be homozygous, that is, each of the two copies of each gene will be identical.
...
[A]ll of the inbred strains, and even the four wild-derived strains, are much closer genetically than previously thought. The study identified 8.27 million different single nucleotide polymorphisms (SNPs). These SNPs are distributed along the genome, but those that are near each other are likely to be inherited together as a group. By creating a map of these groups, or haplotypes, the researchers were able to look at the contributions of each of the four wild-derived strains to the 11 inbred strains, to attribute ancestry. They found that M. m. domesticus contributed the largest part of the 'HapMap,' with 68 percent. The other three wild strains each were responsible for between three and ten percent, with another ten percent of unknown origin, presumably coming from populations of wild mice not represented in the four wild-derived strains.

The whole post is interesting, tracing the development of mouse strains back through breeder Abbie Lathrop to their origins in wild mouse subspecies.

The original research is by Kelly Frazer and colleagues in Nature and Hyuna Yang et al. in Nature Genetics.