9.4 Types of selection

Question 1

What is selection?

Answer 1

The process by which organisms that are better adapted to their environment tend to survive and breed, while those that are less well adapted tend not to.

Question 2

What is directional selection?

Answer 2

selection which favors individuals from one side of the mean of the population, and changes the characteristics of the population.

Question 3

What is stabilizing selection?

Answer 3

selection which favors average individuals, preserving the characteristics of a population.

Question 4

What are phenotypes?

Answer 4

the observable physical and biochemical characteristics of an organism.

Question 5

Describe the process of directional selection.

Answer 5

• during environmental change, the phenotype best suited to the new conditions are most likely to survive. - some individuals which fall towards one side of the mean will possess this phenotype
• these individuals will be more likely to survive and breed.
• they will produce more offspring
• the mean will move in the direction of those individuals.

Question 6

Describe the process of Stabilising selection.

Answer 6

• of environmental conditions remain stable, individuals with phenotypes closest to the mean are most likely to survive.
• they are more likely to pass on their alleles
• individuals at either end of the mean are less likely to pass on their alleles
• stabilising selection eliminates phenotypes at the extremes.

Question 7

Describe the three types of adaptation resulting from natural selection.

Answer 7

ANATOMICAL- such as shorter ears and thicker fur in arctic foxes compared to normal foxes
PHYSIOLOGICAL- such as oxidising of fat rather than carbohydrate in kangaroo rats to produce additional water in desert environments
BEHAVIOURAL- such as the autumn migration of swallows from the UK to Africa to avoid food shortages in the UK winter.