MCQs on Types of Natural Selection - Evolution - Most Important Questions

In this video I have discussed most important questions about Types of Natural Selection.
Based upon different organism - environment relationship. Following different kinds of natural selection have been recognised.
- Stabilising selection.
- Directional selection.
- Disruptive selection.
(1) STABILISING SELECTION :
Stabilizing selection operates when phenotypic feature coincide with optimum environmental conditions and competition is not present. It keeps a population genetically constant. It favours the average or normal phenotypes and eliminate the extreme variants, that fall towards both ends of the bell-shaped curve of variability for the distribution of measurements of phenotypic traits. Due to continuous elimination of both extremes, the bell shaped curve tends to narrow. Stabilising selection always operates in constant or unchanging environment. Ex. Mortality in babies : The birth weight of human babies provides another example influenced by stabilizing selection. The optimum birth weight favoured by stabilizing selection is 7.3 pounds. New born infants less than 5.5 pounds and more than 10 pounds have the highest mortality rate. The curve for mortality is virtually the complement of the curve of survival.
(2) DIRECTIONAL SELECTION :
Directional selection produce a regular change in a population in respect to certain traits. This form of selection operates in response to gradual changes in environmental condition. It favour the phenotype which is non average or extreme and then pushes the phenotype of the population in that direction.
3) DISRUPTIVE SELECTION :
This is probably the rarest form of selection but can be very important in bringing about evolutionary change. Presence of more than one phenotype in a population. Selection pressure acting from within the population as a result increased competition may push the phenotype away from the population mean towards the extremes of the population. This can split a population into two subpopulation. If the gene flow between the subpopulation is prevented, each population may give rise to a new species. In some cases this form of selection can give rise to the appearance of different phenotype within a population, known as polymorphism.
#Directional
#Stabalizing
#Disruptive
#MCQs
Evolution all chapters MCQs
• Evolution