biology : class12 Allele Frequency Changes : Directional Selection, Stabilising Selection, Disruptive Selection : Types of Natural Selection MCQ Questions and Answers
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Allele Frequency Changes
MCQ questions and answers.
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MCQ Questions
1. What happens to the frequency of an allele favored by natural selection over generations?
A.
It usually increases
B.
It always becomes zero
C.
It remains unchanged
D.
It changes only in one individual
Correct Answer:
It usually increases
Explanation:
A favored allele gives an advantage to its carriers, so its frequency usually increases in the population over generations.
2. In directional selection, allele frequency usually shifts toward alleles that produce which type of trait?
A.
The average trait only
B.
One extreme trait
C.
Both extreme traits equally
D.
A completely random trait
Correct Answer:
One extreme trait
Explanation:
Directional selection favors one extreme phenotype, causing the frequencies of alleles associated with that trait to increase.
3. During stabilising selection, alleles associated with average phenotypes are generally expected to:
A.
Increase in frequency
B.
Disappear immediately
C.
Change into new alleles
D.
Be found only in other species
Correct Answer:
Increase in frequency
Explanation:
Stabilising selection favors average phenotypes, so alleles contributing to these phenotypes may become more common.
4. What is a likely allele-frequency effect of disruptive selection?
A.
Alleles for both extreme traits may increase
B.
Only alleles for the average trait increase
C.
All allele frequencies become equal
D.
No allele frequency can change
Correct Answer:
Alleles for both extreme traits may increase
Explanation:
Disruptive selection favors both extreme phenotypes and may increase the frequencies of alleles associated with both extremes.
5. If an allele becomes less useful for survival and reproduction, its frequency in the population may:
A.
Decrease
B.
Always double
C.
Become dominant immediately
D.
Remain fixed in every individual
Correct Answer:
Decrease
Explanation:
Natural selection can reduce the frequency of an allele when it is associated with lower survival or reproductive success.
6. A population has two alleles, and one allele becomes more common after several generations of selection. What has changed?
A.
The allele frequency
B.
The number of chromosomes in every cell
C.
The species name
D.
The age of each organism
Correct Answer:
The allele frequency
Explanation:
Allele frequency is the proportion of a particular allele in a population, and selection can change this proportion across generations.
7. Which type of selection tends to reduce the frequency of alleles associated with both extreme phenotypes?
A.
Stabilising selection
B.
Directional selection
C.
Disruptive selection
D.
Random selection
Correct Answer:
Stabilising selection
Explanation:
Stabilising selection favors the average phenotype and tends to select against both extremes, reducing the success of alleles linked to them.
8. If directional selection favors larger body size, what is likely to happen to alleles promoting larger body size?
A.
Their frequency may increase
B.
Their frequency must become zero
C.
They immediately change into smaller-size alleles
D.
They can no longer be inherited
Correct Answer:
Their frequency may increase
Explanation:
When larger body size is favored, alleles that contribute to it may be passed on more often and increase in frequency.
9. Which selection pattern can maintain or increase alleles for two different extreme phenotypes?
A.
Disruptive selection
B.
Stabilising selection
C.
Directional selection toward the average
D.
Selection with no differences in survival
Correct Answer:
Disruptive selection
Explanation:
Disruptive selection favors both extremes, so alleles associated with the two extreme phenotypes may increase in frequency.
10. Natural selection changes allele frequencies most directly by causing some individuals to:
A.
Leave more offspring than others
B.
Change their alleles during their lifetime
C.
Stop having genes
D.
Produce offspring without DNA
Correct Answer:
Leave more offspring than others
Explanation:
Individuals with advantageous inherited traits may reproduce more successfully, causing their alleles to become more frequent in later generations.
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