Figure 1.—

Asymmetric cline. Allele frequency varies monotonically with latitude, as might be expected in a species in which individuals disperse or migrate along a latitudinal gradient. Phenotype frequency varies to a greater extent, as might be expected, for example, if temperature, represented by the shading, produces selective pressure in favor of one particular phenotype. The genotype and phenotype curves are constants plus functions asymmetric around the center of the range of latitudes. In this example, with uniform sampling by latitude, spurious associations will occur.