In
population genetics,
directional selection is a mode of
natural selection in which an extreme
phenotype is favored over other phenotypes, causing the
allele frequency to shift over time in the direction of that phenotype. Under directional selection, the advantageous allele increases as a consequence of differences in survival and reproduction among different phenotypes. The increases are independent of the dominance of the allele, and even if the allele is
recessive, it will eventually become
fixed.