Question

Define the three types of selection and provide an example of each. (please type for easier read)

Answer 1

Selection/ Natural selection :-
• This is mechanism of evolution.
• "More adaptated organisms have more chances to survive.

Types -
There are three types of selection - Stabilizing selection, Directional selection and Disruptive selection.

Stabilizing selection :-
• Intermediate phenotypes are more fit, adaptated and have more chances of survival then extreme phenotypes.
• It favours the normal phenotype and eliminates the extreme phenotypes.
Example - Mortality in human babies.
• The optimum birth weight favoured by stabilizing selection is 7.3 pounds, newborns less then 5.5 pounds and more then 10 pounds birth weight have less chances of survival and have high mortality rate.

Directional selection :-
• One extreme phenotype has more chances of survival then other extreme and mean phenotype.
• One extreme phenotype is favoured and other extreme and mean phenotypes are eliminated.
Example - DDT resistant in pests.
• Pests which are resistant to DDT are selected and sensitive pests are eliminated from population.

Disruptive selection :-
• In this type of selection, members of both extreme phenotypes are selected and mean or intermediate phenotype members are eliminated.
• Both extreme phenotypes are more fit then intermediate phenotype.
• After selection, two peaks are formed.
Example - In a environment with white and black rocks, white and black rabbits will selected and grey rabbits will eliminated, because white and black rabbits are able to hide easily in rocks whereas grey rabbits are unable to hide and all these rabbits eaten by predators.