biology : class12 Reduction in Phenotypic Variation : Directional Selection, Stabilising Selection, Disruptive Selection : Types of Natural Selection MCQ Questions and Answers
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Reduction in Phenotypic Variation
MCQ questions and answers.
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MCQ Questions
1. Which type of natural selection most directly reduces phenotypic variation by favouring intermediate individuals?
A.
Directional selection
B.
Stabilising selection
C.
Disruptive selection
D.
Random selection
Correct Answer:
Stabilising selection
Explanation:
Stabilising selection favours intermediate phenotypes and selects against extreme phenotypes, thereby reducing phenotypic variation in the population.
2. In stabilising selection, which individuals are usually selected against?
A.
Only individuals with intermediate traits
B.
Individuals with extreme traits
C.
All individuals equally
D.
Only newly born individuals
Correct Answer:
Individuals with extreme traits
Explanation:
By removing individuals at both extremes, stabilising selection leaves more individuals with similar intermediate phenotypes and reduces phenotypic variation.
3. A population of birds has mostly medium-sized beaks after selection because birds with very small and very large beaks survive less well. What is the likely result?
A.
Increased phenotypic variation
B.
Reduced phenotypic variation
C.
Formation of two distinct groups
D.
No change in the phenotype distribution
Correct Answer:
Reduced phenotypic variation
Explanation:
Selection against both extreme beak sizes increases the proportion of medium-sized beaks, reducing variation in beak size.
4. Which phenotype distribution is most likely after strong stabilising selection?
A.
A narrow range around the intermediate phenotype
B.
Two widely separated groups
C.
A range shifted completely toward one extreme
D.
An equal number of every phenotype
Correct Answer:
A narrow range around the intermediate phenotype
Explanation:
Stabilising selection removes extreme phenotypes, so the population becomes concentrated around the intermediate phenotype.
5. How does stabilising selection affect extreme phenotypes in a population?
A.
It increases their frequency
B.
It decreases their frequency
C.
It changes them into intermediate phenotypes immediately
D.
It makes all phenotypes equally common
Correct Answer:
It decreases their frequency
Explanation:
Lower survival or reproduction of extreme phenotypes causes them to become less common, reducing phenotypic variation.
6. Which example best shows reduction in phenotypic variation through stabilising selection?
A.
Medium-weight newborns survive better than very small or very large newborns
B.
Dark-coloured insects become more common than light-coloured insects
C.
Both very small and very large seeds are favoured
D.
Individuals with different traits survive equally well
Correct Answer:
Medium-weight newborns survive better than very small or very large newborns
Explanation:
Favouring an intermediate body weight and selecting against both extremes reduces the range of body weights in the population.
7. What happens to the range of phenotypes when selection removes individuals at both extremes?
A.
The range usually becomes narrower
B.
The range always becomes wider
C.
The range splits into two groups
D.
The range becomes unrelated to survival
Correct Answer:
The range usually becomes narrower
Explanation:
Removing both extreme phenotypes leaves fewer forms at the ends of the range, causing an overall reduction in phenotypic variation.
8. Which type of selection is commonly associated with a decrease in phenotypic variation around an average trait?
A.
Stabilising selection
B.
Disruptive selection
C.
Directional selection
D.
Artificial mutation
Correct Answer:
Stabilising selection
Explanation:
Stabilising selection favours the average phenotype and removes extremes, producing reduced phenotypic variation around the average.
9. If only individuals with an intermediate height reproduce successfully, what is expected in future generations?
A.
A greater concentration of intermediate heights
B.
A greater concentration of both extreme heights
C.
The disappearance of all height differences immediately
D.
An equal frequency of all heights
Correct Answer:
A greater concentration of intermediate heights
Explanation:
Successful reproduction by intermediate individuals and reduced success of extreme individuals narrows the phenotypic range.
10. Which statement correctly describes the effect of stabilising selection on phenotypic variation?
A.
It favours extremes and increases variation
B.
It favours intermediate forms and reduces variation
C.
It creates two extreme forms and reduces the average
D.
It has no relationship with phenotype frequencies
Correct Answer:
It favours intermediate forms and reduces variation
Explanation:
Stabilising selection preserves intermediate phenotypes while selecting against extremes, which reduces the differences among individuals.
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