Evolutionary Mechanisms MCQ Quiz - Objective Question with Answer for Evolutionary Mechanisms - Download Free PDF

The correct answer is A: False, B: True, C: False, D: True

Concept:

• Evolution by natural selection is a fundamental mechanism driving the diversity of life. It favors traits that enhance survival and reproduction in a given environment.
• Adaptation refers to the process where organisms evolve traits that allow them to function better in their environment. However, adaptation does not imply perfection, and various constraints can influence the process.
• The traits we see today are shaped by past environments, and adaptation is not limited to the current environment but reflects historical interactions with selection pressures.
• Natural selection is one of many processes influencing evolution. Other mechanisms, like genetic drift, gene flow, and mutation, also play roles in shaping traits.

Explanation:

• A: False: Adaptation does not imply that organisms are perfectly matched to their current environment. Evolution works on available genetic variation and may lead to traits that are "good enough" rather than perfect. Additionally, environments can change faster than evolution can adapt organisms to them, leaving mismatches.
• B: True: Adaptive traits are shaped by natural selection acting on past environments. Evolution is influenced by historical selection pressures, meaning traits that were advantageous in the past may still persist even if the current environment has changed.
• C: False: While natural selection is a primary mechanism driving adaptation, it is not the only process. Other evolutionary processes, such as genetic drift (random changes in allele frequencies) and gene flow (movement of genes across populations), can also influence traits and their prevalence in populations.
• D: True: Adaptation to current environments may be constrained by adaptations to past environments. For example, traits that evolved for past environments may limit the ability to adapt to new environments, creating evolutionary "trade-offs."

The correct answer is 5.76

Explanation:

• The Hardy-Weinberg equilibrium principle states that allele and genotype frequencies in a population will remain constant from generation to generation in the absence of evolutionary influences.

To calculate the expected genotype frequencies under Hardy-Weinberg equilibrium, we use the formula:

• Frequency of genotype = (frequency of allele 1) × (frequency of allele 2).
• Here, "AaBb" is a genotype that involves heterozygosity for both genes (A and B). For heterozygous genotypes, the calculation combines probabilities of each allele pairing.
• Given Data:
  • Frequency of allele 'a' = 0.2
  • Frequency of allele 'A' = 1 - 0.2 = 0.8
  • Frequency of allele 'b' = 0.1
  • Frequency of allele 'B' = 1 - 0.1 = 0.9
• Genotype AaBb:
  • Since AaBb involves heterozygosity (one dominant and one recessive allele for each gene), the probability can be calculated as follows:
  • Frequency of Aa = 2 × (frequency of A × frequency of a) = 2 × (0.8 × 0.2) = 0.32
  • Frequency of Bb = 2 × (frequency of B × frequency of b) = 2 × (0.9 × 0.1) = 0.18
  • Frequency of AaBb = Frequency of Aa × Frequency of Bb = 0.32 × 0.18 = 0.0576
  • Expected genotype population with AaBb = 5.76%

The correct answer is A shows negative selection, B shows positive selection.

Concept:

In evolutionary biology, genetic mutations can be categorized into synonymous and non-synonymous mutations:

• Synonymous mutations: These are mutations in the DNA sequence that do not result in a change in the amino acid sequence of the protein. They are often considered neutral as they do not affect protein function.
• Non-synonymous mutations: These are mutations that lead to a change in the amino acid sequence of the protein, potentially altering its function. These mutations can be advantageous, deleterious, or neutral depending on the selective pressures acting on them.

The selection pressures acting on a population can be classified as:

• Negative selection: Also known as purifying selection, it removes deleterious mutations, reducing the prevalence of non-synonymous mutations compared to synonymous ones.
• Positive selection: This favors advantageous mutations, increasing the prevalence of non-synonymous mutations in the population.
• Neutral selection: Mutations (both synonymous and non-synonymous) accumulate randomly without any selective advantage or disadvantage.

Explanation:

• Phylogeny A: In Phylogeny A, the distribution of mutations suggests negative selection. Negative selection is characterized by a higher proportion of synonymous mutations (solid black circles) compared to non-synonymous mutations (different symbols). This indicates that deleterious non-synonymous mutations are being removed from the population, consistent with purifying selection.
• Phylogeny B: In Phylogeny B, the pattern indicates positive selection. Positive selection is evidenced by a higher prevalence of non-synonymous mutations, suggesting that these mutations are advantageous and being favored in the population.

The correct answer is A, B, and D

Concept:

• Genetic drift is a mechanism of evolution that refers to random changes in allele frequencies within a population over time. It occurs independently of natural selection and is particularly pronounced in small populations.
• Key characteristics of genetic drift:
  • It is a random process, meaning it is not influenced by the fitness or advantage of alleles.
  • It can lead to the fixation of certain alleles (allele frequency reaching 100%) purely by chance, while others are lost.
  • Genetic drift reduces genetic diversity over time, as some alleles are eliminated from the population.
  • The effects of genetic drift are more significant in small populations due to the higher likelihood of random events altering allele frequencies drastically.

Explanation:

• Statement A: "Fixation of an allele is purely by chance, while other alleles are lost."
  • This is correct. Genetic drift is a random process that can lead to the fixation of certain alleles purely by chance, while other alleles disappear from the gene pool.
• Statement B: "Genetic drift can lead to the loss of certain alleles over time, reducing genetic diversity within the population."
  • This is correct. Genetic drift reduces genetic variation because some alleles are lost completely due to random events, especially in small populations.
• Statement C: "Changes in allele frequencies are due to positive selection."
  • This is incorrect. Positive selection refers to the process where advantageous alleles increase in frequency due to their beneficial effects on the organism’s fitness, which is not a random process. Genetic drift, on the other hand, is entirely random and independent of fitness.
• Statement D: "There is a pronounced effect in small populations, where random events can drastically alter allele frequencies."
  • This is correct. Genetic drift has a much stronger effect in small populations, where random changes in allele frequencies can have a more significant impact on the overall gene pool.

The correct answer is:Convergent evolution

Explanation:

• Option 1: Genetic drift

  • False: Genetic drift refers to random changes in allele frequencies in a population, particularly in small populations. It does not explain the development of similar traits in different species.

• Option 2: Divergent evolution

  • False: Divergent evolution occurs when two related species evolve different traits due to different environmental pressures or niches. In this case, the species are not evolving different traits, but similar traits independently.

• Option 3: Allopatric speciation

  • False: Allopatric speciation refers to the formation of new species due to geographic isolation, leading to reproductive isolation. It does not explain the development of similar traits in different species.

• Option 4: Convergent evolution

  • True: Convergent evolution occurs when different species, not closely related, independently evolve similar traits or features, often due to similar environmental pressures or ecological niches. In this case, the Asian mongoose and American skunk have evolved the ability to spray musk independently due to similar selective pressures.

 Key Points

• Convergent evolution often results in analogous structures, which serve similar functions but have different evolutionary origins. The musk spraying behavior in both animals is an example of such analogous traits.
• The development of similar traits in different species can also be influenced by similar environmental challenges, such as the need for defense mechanisms against predators.

The correct answer is Option 1 i.e.64

Concept:

• Hardy Weinberg's principle relates genotypic frequency and allelic frequency in a population that is mating randomly. 
• Hardy Weinberg equilibrium states that in the absence of external disruption, genotypic frequencies in a population remain stable across generations.
• Hardy Weinberg equation is given by 
• \(p^2 + 2pq + q^2 = 1 \)
• Here, the p and q represent the frequency of the dominant allele and recessive allele, and \(p^2, 2pq\) and \(q^2\)represent the frequency of homozygous dominant, heterozygous and homozygous recessive.
• Random mating, infinite population size,  no mutation, no gene flow, and no selection are assumptions of Hardy-Weinberg equilibrium.

Explanation:

• Frequency of homozygous recessive phenotype \(q^2 = 0.04 \)
• Then the frequency of recessive allele = q=0.2
• According to the Hardy-Weinberg equilibrium, \(p+q=1\)
• Now, the frequency of the dominant allele (p) is:

  \(\begin {equation} \begin {split} p &= 1-q \\&= 1-0.2 \\&= 0.8\\ \end {split} \end {equation}\)

• Frequency of homozygous dominant phenotype \(=p^2\)
• Therefore, the frequency of homozygous dominant individuals in the population is:

\(\begin{equation} \begin {split} p^2 &= 0.8 \times 0.8 \\ p^2 &= 0.64 \end {split} \end {equation} \)

• The percentage of individuals homozygous for the dominant allele is 64%.

Hence, the correct answer is Option 1.

The correct answer is Genotype frequencies: 0.64 WW 0.32 Ww and 0.04 Ww Allele Frequencies W-0.8 and w-0.2

Explanation:
The total population size is given as 500 individuals.

Given genotypes:

• WW: 320 individuals
• Ww: 160 individuals
• ww: 20 individuals

Genotype frequency is calculated as the number of individuals with the genotype divided by the total population size.

• Frequency of WW (p²): Frequency of WW = no of WW individuals / Total no of indiviuals = 320/500= 0.64
• Frequency of Ww (2pq): No. of Ww individuals / Total no of individuals = 160/500= 0.32
• Frequency of ww (q²): No of ww individuals / Total no of individuals= 20/500= 0.04

Calculate the total number of each allele in the population. Each individual contributes two alleles.

Number of W alleles:

• From WW individuals: ( 320 X 2 = 640 )
• From Ww individuals: ( 160 X 1 = 160 )
• Total W = 640 + 160=800

Number of w alleles:

• From ww individuals: ( 20 X 2 = 40 )
• From Ww individuals: ( 160 X 1 = 160 )
• Total w = 40+160= 200

Next, calculate the total number of alleles in the population:

Total alleles in the population = 2 x (Number of individuals} = 2 x 500 = 1000 

Now, determine the allele frequencies:

• Frequency of W (p): 800/1000= 0.8
• Frequency of w (q): 200/1000 = 0.2

Summary
Genotype Frequencies:

• WW: 0.64
• Ww: 0.32
• ww: 0.04

Allele Frequencies:

• W: 0.8
• w: 0.2

Concept:

• The Hardy-Weinberg equilibrium is a principle stating that the genetic variation in a population will remain constant from one generation to the next in the absence of disturbing factors.
• When mating is random in a large population with no disruptive circumstances, the law predicts that both genotype and allele frequencies will remain constant because they are in equilibrium.

Explanation:

• The Hardy-Weinberg equation is a mathematical equation that can be used to calculate the genetic variation of a population at equilibrium.
• The equation is an expression of the principle known as Hardy-Weinberg equilibrium, which states that the amount of genetic variation in a population will remain constant from one generation to the next in the absence of disturbing factors.
• The Hardy-Weinberg equation is expressed as:

• In the equation, p2 represents the frequency of the homozygous genotype AA, q2 represents the frequency of the homozygous genotype aa, and 2pq represents the frequency of the heterozygous genotype Aa.
•  In the given question heterozygote will be 2pq X 300, i.e., 2 X 0.7 X 0.3 X 300 = 126

Hence the correct answer is Option 3

The correct answer is Option 1 i.e.64

Concept:

• Hardy Weinberg's principle relates genotypic frequency and allelic frequency in a population that is mating randomly. 
• Hardy Weinberg equilibrium states that in the absence of external disruption, genotypic frequencies in a population remain stable across generations.
• Hardy Weinberg equation is given by 
• \(p^2 + 2pq + q^2 = 1 \)
• Here, the p and q represent the frequency of the dominant allele and recessive allele, and \(p^2, 2pq\) and \(q^2\)represent the frequency of homozygous dominant, heterozygous and homozygous recessive.
• Random mating, infinite population size,  no mutation, no gene flow, and no selection are assumptions of Hardy-Weinberg equilibrium.

Explanation:

• Frequency of homozygous recessive phenotype \(q^2 = 0.04 \)
• Then the frequency of recessive allele = q=0.2
• According to the Hardy-Weinberg equilibrium, \(p+q=1\)
• Now, the frequency of the dominant allele (p) is:

  \(\begin {equation} \begin {split} p &= 1-q \\&= 1-0.2 \\&= 0.8\\ \end {split} \end {equation}\)

• Frequency of homozygous dominant phenotype \(=p^2\)
• Therefore, the frequency of homozygous dominant individuals in the population is:

\(\begin{equation} \begin {split} p^2 &= 0.8 \times 0.8 \\ p^2 &= 0.64 \end {split} \end {equation} \)

• The percentage of individuals homozygous for the dominant allele is 64%.

Hence, the correct answer is Option 1.

The correct answer is Option 1 i.e.Evolution by natural selection is progressive, it makes individuals 'better'.

Concept:

• Natural selection is a key mechanism of evolution that explains how populations of organisms change over time.
• It is a process by which individuals with certain advantageous traits are more likely to survive and reproduce, passing their beneficial traits on to their offspring, while those with less advantageous traits are less likely to survive and reproduce, and their traits may be lost over time.
• The basic idea behind natural selection is that trait that increase an organism's ability to survive and reproduce in a particular environment will be passed on to future generations at a higher rate than traits that do not.
• Over time, this leads to changes in the frequency of traits in a population, as certain traits become more common and others become less common.

Important Points

Option 1 - FALSE

• While natural selection can lead to the evolution of traits that improve an organism's fitness in a particular environment, it is not inherently progressive or goal-oriented.
• Natural selection is a process that acts on the variation present in a population and favors traits that confer an advantage in a particular environment.
• This means that what is advantageous or "better" can vary depending on the environment and the selective pressures acting on a population.
• Therefore, it is incorrect to say that natural selection always leads to individuals becoming "better".

Option 2 - TRUE

• Natural selection acts on the variation present in individuals, but the changes in trait frequencies that result from selection occur at the population level over time.

Option 3 - TRUE

• Natural selection does not directly cause genetic changes in individuals but rather acts on the variation that is already present in a population.
• Over time, the cumulative effects of selection on trait frequencies can lead to genetic changes in populations.

Option 4 - TRUE

• Natural selection acts on the observable traits of organisms, or phenotypes, which are the result of interactions between an organism's genotype and its environment.
• It is the phenotype that affects an organism's fitness and determines whether or not it will be selected for or against in a particular environment.

Therefore, the correct answer is Option 1.

The correct answer is stabilizing.

Explanation:

Stabilizing selection favors individuals with intermediate values of a trait, reducing variation around the mean. It does not increase variation.

• An example of this is human birth weight — babies of low weight lose heat more rapidly and get ill from infectious diseases more easily, while babies of large weight are more difficult to deliver. Babies of medium weight survive most often.
• Directional selection tends to favor one extreme phenotype, thus changing the average value of a trait.
• Stabilizing selection favors intermediate variants and acts against extreme phenotypes, reducing variation in a trait over time.
• Disruptive selection favors the extreme phenotypes over intermediates, thereby increasing variation in a trait. Disruptive selection favors individuals at both extremes of a trait, leading to an increase in variation. It promotes the divergence of traits within a population.
• Balancing selection maintains variation in a trait, as multiple alleles are actively maintained in the gene pool.

The correct answer is 12.5

Explanation:

• Random genetic drift is the change in the frequency of an existing gene variant (allele) in a population due to random sampling of organisms.
• Genetic drift acts more strongly in small populations and can lead to the fixation or loss of alleles over time.
• In a population of 12 individuals, with 2 Bb genotype and 10 BB genotypes.
• Each individual has 2 alleles, so there are (12 x 2 = 24) alleles in total per population. 
• The initial frequency of the "b" allele is 2/24 = 1/12
• Over a large number of generations, genetic drift can lead to either the loss or fixation of the "b" allele in each population.
• The probability of the "b" allele getting fixed in a population is equal to its initial frequency.
• In this case, the initial frequency of the "b" allele is 1/12.

Therefore, out of 150 independent populations, the expected number of populations in which the "b" allele becomes fixed is 1/12 x 150 = 12.5.

The correct answer is Genotype frequencies: 0.64 WW 0.32 Ww and 0.04 Ww Allele Frequencies W-0.8 and w-0.2

Explanation:
The total population size is given as 500 individuals.

Given genotypes:

• WW: 320 individuals
• Ww: 160 individuals
• ww: 20 individuals

Genotype frequency is calculated as the number of individuals with the genotype divided by the total population size.

• Frequency of WW (p²): Frequency of WW = no of WW individuals / Total no of indiviuals = 320/500= 0.64
• Frequency of Ww (2pq): No. of Ww individuals / Total no of individuals = 160/500= 0.32
• Frequency of ww (q²): No of ww individuals / Total no of individuals= 20/500= 0.04

Calculate the total number of each allele in the population. Each individual contributes two alleles.

Number of W alleles:

• From WW individuals: ( 320 X 2 = 640 )
• From Ww individuals: ( 160 X 1 = 160 )
• Total W = 640 + 160=800

Number of w alleles:

• From ww individuals: ( 20 X 2 = 40 )
• From Ww individuals: ( 160 X 1 = 160 )
• Total w = 40+160= 200

Next, calculate the total number of alleles in the population:

Total alleles in the population = 2 x (Number of individuals} = 2 x 500 = 1000 

Now, determine the allele frequencies:

• Frequency of W (p): 800/1000= 0.8
• Frequency of w (q): 200/1000 = 0.2

Summary
Genotype Frequencies:

• WW: 0.64
• Ww: 0.32
• ww: 0.04

Allele Frequencies:

• W: 0.8
• w: 0.2

The correct answer is 192

Explanation:

1. Population and Allele Frequency:

• The total population = 400 individuals.
• Number of non-tasters (homozygous recessive, pp) = 64.

According to the Hardy-Weinberg principle, the frequency of the homozygous recessive genotype (pp) can be represented as q² , where q is the frequency of the recessive allele (p).

2. Calculate the Frequency of the Recessive Allele (p):

• q² = \(\frac{64}{400} = 0.16 \).
• q = \(\sqrt{0.16} = 0.4 \).

3.Calculate the Frequency of the Dominant Allele (P):

• The frequency of allele P, denoted as p, can be calculated since p + q = 1
• p = 1 - q = 1 - 0.4 = 0.6.

4. Calculate the Frequency of the Heterozygous Genotype (Pp):

• According to Hardy-Weinberg, the frequency of the heterozygous genotype (Pp) is represented by 2pq.
• 2pq = 2 x 0.6 x 0.4 = 0.48

5.Calculate the Number of Heterozygous Individuals:

• The number of individuals with genotype Pp = Total population × Frequency of Pp.
• 400 x 0.48 = 192.

Therefore, the number of heterozygous individuals (Pp) in this population is 192.

Concept:

• Hardy–Weinberg Equilibrium (HWE) is a null model of the relationship between allele and genotype frequencies, both within and between generations, under assumptions of no mutation, no migration, no selection, random mating, and infinite population size.

Explanation:

The Hardy-Weinberg law rests on these assumptions:

• The population under study is large, and matings are random with respect to the locus in question.
• Allele frequencies remain constant over time because of the following:

1. There is no appreciable rate of new mutation.
2.  Individuals with all genotypes are equally capable of mating and passing on their genes; that is, there is no selection against any particular genotype.
3. There has been no significant immigration of individuals from a population with allele frequencies very different from the endogenous population.
4. A population that reasonably appears to meet these assumptions is considered to be in Hardy-Weinberg equilibrium.

       hence the correct answer is option 4