Allele Frequencies. Allele frequencies of the 23- and 12-bp insertion/deletion polymorphisms in UK Holstein, German Holstein, German Brown and German Fleckvieh BSE affected (red) and control (light-blue) animals. "1" and "2" above the columns represent the deletion and insertion alleles, respectively. The horizontal black lines indicate the expected proportions of cases and controls in each class. The thickness of the columns is proportional to the allele frequency. Asterisks indicate the level of significance: * < 0.05, ** < 0.01, *** < 0.001.