Figure 2.—

Symmetric cline. Allele frequency varies monotonically with altitude, as might be expected in a species in which individuals disperse or migrate along a mountain slope. Phenotype frequency varies to a greater extent, as might be expected, for example, if altitude produces selective pressure in favor of one particular phenotype. The genotype curve is a constant plus an asymmetric function, and the phenotype curve is a constant plus a symmetric function. In this example, with a sampling scheme symmetric around the mountain peak, no spurious associations will occur.