Types of Selection

• What is selection?


  The process by which organisms that are better adapted to their environment tend to survive and breed.
• What is directional selection?


  Selection that favours phenotypes that vary in one direction from the mean of the population, producing a gradual change in allele frequency.
• What is stabilising selection?

  Selection that favours average phenotypes and preserves the characteristics and alleles of a population.
• What is more than one gene called?

  Polygene.
• What do different characteristics favour?


  Different characteristics in the population.
• What are most characteristics influenced by?

  More than one gene.
• What are characteristics influenced by more than one gene more influenced by?

  The environment.
• What does the effect of the environment have on polygenes?

  It produces individuals in a population that vary about the mean.
• What graph can we plot to show the variation between individuals effected by the environment?

  A normal distribution curve.
• What is a phenotype?


  The observer physical and biochemical characteristics of an organism.
• What does it mean in directional selection if the individuals fall to either the left or right of the mean?

  They will possess a phenotype more suited to the new conditions and will be more likely to survive and breed, contributing more offspring and their alleles.
• What are selection pressures?

  Environmental factors that affect the chance of survival of an organism.
• What is an example of a selection pressure?

  High competition for food between predators.
• What is an example of directional selection?


  Antibiotic-resistant bacteria strains becoming more common.
• What is an example of stabilising selection?

  Very low and very high birth weight in humans are selected against leading to the maintenance of the intermediate weight.
• What adaptations may natural selection result in?

  Anatomical, physiological, and behavioural.