What is the best definition of directional selection
The Correct Answer and Explanation is:
Directional selection is a type of natural selection that occurs when an environmental or ecological change favors one extreme phenotype over others within a population. Over time, this leads to a shift in the population’s trait distribution, moving it in the direction of the favored trait.
In directional selection, the allele frequencies shift toward the beneficial extreme trait. This often happens when an environmental change, such as climate or availability of food, favors one side of the trait spectrum. For instance, in a population of birds, if larger beaks allow individuals to access a new food source, birds with larger beaks may have better survival rates. Over many generations, the population would then shift toward having larger beaks as the trait becomes more common in the population.
Directional selection is commonly seen during periods of environmental change or when a new selective pressure arises, such as a change in the climate or introduction of a new predator. For example, when a new predator arrives in an area, individuals who can run faster or have better camouflage may be more likely to survive and reproduce. This advantage leads to the increase in frequency of traits associated with speed or camouflage over generations.
It’s important to note that directional selection doesn’t always result in the elimination of other traits. Rather, it shifts the population towards a more favorable phenotype. However, it may reduce genetic variation within a population, as the trait being selected for becomes dominant over time.
An example of directional selection in action is the evolution of antibiotic resistance in bacteria. When exposed to antibiotics, bacteria with resistance genes are more likely to survive and reproduce, leading to an increase in antibiotic-resistant strains over time.
