TYPES OF NATURAL SELECTION

In the previous blog, I explained what natural selection is about. Today, I will delve into the different ways in which it is classified.

SELECTION BASED EFFECT ON A TRAIT

1. Stabilizing selection: This acts in such a way that the trait is held at a stable optimum. For example, tall plants in a forest are susceptible to being blow down by the wind; short plants are susceptible to competition for sunlight; so that compromise leads to the development of medium height plants.

2. Directional selection: This acts during transitional periods when the current mode of the trait is sub-optimal, and alters the trait towards a single new optimum. For example, the shortage of food at ground level made it difficult for the giraffe with short necks to survive. The development of long necks

3. Disruptive selection: This acts during transitional periods when the current mode is sub-optimal, but alters the trait in more than one direction. Example: If there are three types of plants in an area, tall, medium, and short, that are pollinated by three individuals. If the pollinator of the medium plant is no more there, the medium plant's population will decrease while that of the short and tall will remain. 

SELECTION BASED ON EFFECT ON ALLELE FREQUENCY

1. Positive selection: This effect leads to an increase frequency of an allele.

2. Negative selection: This effect leads to a decrease in the frequency of an allele.

SELECTION BASED ON EFFECT ON GENETIC DIVERSITY

1. Purifying selection: This acts to remove the genetic variation in a population.

2. Balancing selection: This acts to maintain the genetic variation in a population.