directional selection Natural selection that favours the establishment of one particular advantageous mutation within a population, resulting in a change in phenotype in that direction. An example of directional selection is the increase in darker forms of the peppered moth (Biston betularia) that occurred in industrial areas, where the moths with darker wing coloration are better camouflaged than those with lighter wings against polluted tree trunks (see industrial melanism). Compare disruptive selection; stabilizing selection.

directional selection A selection that operates on the range of phenotypes for a particular characteristic existing in a population, by moving the mean phenotype towards one phenotypic extreme. Directional selection usually occurs in response to a steady change in environmental conditions, with a consequent shift in selection pressure such that the frequency of particular alleles will change in a constant direction. It is often used in agriculture and horticulture to produce a shift in the population mean of a trait derived by humans. For example, the breeder might select for cows that yield more milk or plants that fruit only in a particular season. Compare disruptive selection and stabilizing selection.

directional selection A selection that operates on the range of phenotypes for a particular characteristic existing in a population, by moving the mean phenotype towards one phenotypic extreme. Directional selection usually occurs in response to a steady change in environmental conditions, with a consequent shift in selection pressure such that the frequency of particular alleles will change in a constant direction. It is often used in agriculture and horticulture to produce a shift in the population mean of a trait derived by humans. For example, the breeder might select for plants that fruit only in a particular season. Compare DISRUPTIVE SELECTION.

directional selection Selection that changes the frequency of an allele in a particular, constant direction, either towards or away from fixation of that allele. It is often used in agriculture and horticulture to produce a shift in the population mean of a trait desired by humans. For example, the breeder might select for cows that yield more milk. Compare DISRUPTIVE SELECTION; STABILIZING SELECTION.