The disease known as Septoria nodorum blotch, or SNB, is caused by a fungal pathogen that infects wheat plants and can cause substantial losses in grain yield. When a specific protein known as Tox1 is produced by the fungus and it is recognized by the wheat gene named Snn1, there is a compatible interaction that leads to disease in the wheat plant. Here, researchers conducted genetic, genomic, and bioinformatic analyses to determine how the Snn1 gene evolved, characterize the level of genetic diversity among wheat lines that carry the Snn1 gene, determine how the Snn1 gene functions to recognize the fungal SnTox1 protein, and to develop molecular markers that can be used by wheat breeders to track the Snn1 gene. The researchers found that some wheat lines carry two copies of Snn1, and the second copy resulted from a relatively recent genetic duplication of the first copy. Specific features in the DNA of the Snn1 genes were identified that dictate whether Snn1 can recognize SnTox1 thereby making the wheat plant either resistant or susceptible to SNB. These features were targeted for the development of several molecular markers that can be used in efficient DNA assays to determine if the Snn1 gene is present, and therefore if a given wheat plant will be resistant or susceptible to SNB. These marker assays will serve as useful tools to wheat breeders for the efficient development of SNB-resistant wheat varieties.