The hereditary ataxias are categorized by mode of inheritance and causative gene or chromosomal locus. The variation in sensitivity is determined by two common alleles at the TAS2R38 locus. Lactase is encoded by a single genetic locus on chromosome 2. The precise identity of the gene at the "Orange" locus is unknown. Underdominance of the locus is another possibility of phenotypic expression. Cross hybridizations indicate the phenotypes are produced by isoalleles at a single locus. See also the definition of a genetic locus. Degeneration is also present in brainstem nuclei like the locus coeruleus. Opioids inhibit the firing of neurons in the locus coeruleus. Changes in the electrophysiological properties of cells in the locus ceruleus were shown. This theory approaches two methods of inquiry including locus of causality and stability. Haploid yeast switch mating type by replacing the information present at the "MAT" locus. The outer curved boundary is the "spectral locus", with wavelengths shown in nanometers. This property is inherited by the connectedness locus of real cubic polynomials. CTCF is present in both the chicken formula 1-globin locus and human formula 1-globin locus.