Genetic crosses between the two species of Peromyscus mice reveal that the derived burrows of oldfield mice are dominant and evolved through the addition of multiple genetic changes. Quantitative trait locus analysis indicates that tunnel length segregates as a complex trait, affected by at least three independent genetic regions, whereas the presence of an escape tunnel is associated with only a single locus.

http://www.ncbi.nlm.nih.gov/pubmed/23325221

Jesse N. Weber, Brant K. Peterson, Hopi E. Hoekstra; Nature, 2013; 493:402-406 [DOI:10.1038/nature11816]

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