Organic Evolution Questions and Answers

Q: Variation maintained in a population with Mendelian inheritance is explained by :

It is explained by the Hardy-Weinberg principle.Under Mendelian (particulate) inheritance, alleles pass unchanged from generation to generation. Hardy and Weinberg (1908) showed that, in a large randomly mating population without mutation, migration, selection or drift, allele and genotype frequencies stay constant (\(p^{2} + 2pq + q^{2} = 1\)), so variation is conserved rather than lost.Blending inheritance would halve variation in every generation, which was a serious problem for Darwin's theory. Natural selection changes allele frequencies rather than preserving them, and spontaneous generation is a discredited idea about the origin of life.

Q: Based on molecular evolution, which one of the following is close to humans ?

The closest to humans are the African apes.DNA and protein comparisons show that humans are most closely related to the African apes, chimpanzees and bonobos above all, with whom we share about 98-99% of our DNA sequence, followed by gorillas. The human and chimpanzee lineages separated roughly 6-7 million years ago.Orangutans, the Asian great apes, branched off earlier (about 13-16 million years ago), gibbons (the lesser apes) earlier still, and lemurs are prosimians, among the most distant primates from humans.

Q: Which of the following statements is NOT true ?

The statement that is NOT true is In diversifying selection, no extreme phenotypes are favoured.Diversifying (disruptive) selection does the opposite: it favours both extremes of the range and acts against the intermediate forms, which can split a population into two distinct types.The other statements follow the textbook account. Directional selection favours variants at one extreme and shifts the population mean that way. Stabilizing selection acts against both extremes and favours the average. And where the favoured intermediate is a heterozygote, as with the sickle-cell allele in malarial regions, selection for the middle keeps both alleles in the population, a balanced polymorphism. So the only statement that contradicts the definitions is the one about diversifying selection.

Q: Which of the following is NOT a premating mechanism of isolation ?

The one that is not a premating mechanism is zygotic mortality.Premating (prezygotic) barriers stop mating or fertilisation from happening: temporal isolation (breeding at different times), behavioural isolation (different courtship signals) and mechanical isolation (incompatible genitalia or flower structure).Zygotic mortality acts after fertilisation, when the hybrid zygote or embryo dies, so it is a postmating (postzygotic) barrier, along with hybrid inviability and hybrid sterility.

Q: A clade is a set of species :

A clade is a set of species derived from a common ancestor.In cladistics a clade, or monophyletic group, consists of a single ancestor and all of its descendants; it is one complete branch of the tree of life. Birds, for example, form a clade within the dinosaurs.A group derived from two or several unrelated ancestors would be polyphyletic, which cladistics rejects as a natural grouping. Species sharing a particular environment form an ecological group, not a clade.

Q: The population of asiatic lion is small. Therefore, there is greater chance of :

A small population has a greater chance of genetic drift.Genetic drift is the random change in allele frequencies from one generation to the next due to chance in which individuals breed. Its effect is strongest in small populations, where alleles can be lost or fixed quickly. The Asiatic lions of Gir, descended from a very small number of survivors, show low genetic variation for this reason.Gene flow needs migration between populations, the mutation rate does not depend on population size, and selection acts in populations of any size; only drift is specifically intensified by smallness.

Q: During the evolution of life, the first formed cells were :

The first cells were Chemoheterotrophs.On the classical Oparin-Haldane account, which this question follows, the first cells arose in a 'primordial soup' rich in organic molecules made abiotically. They used those ready-made molecules as both energy and carbon source, anaerobically, which makes them chemoheterotrophs.Photoautotrophs needed the more complex machinery of photosynthesis and came later. Saprotrophs feed on dead organisms, which could not exist before life did. Chemoautotrophs, which build organic matter from inorganic chemicals, are favoured by some newer theories but are not the textbook answer.

Q: During the evolution of life, the first formed photosynthetic organisms were :

The first photosynthetic organisms among those listed were cyanobacteria.Cyanobacteria are prokaryotes that carried out oxygen-releasing photosynthesis long before eukaryotes existed; their mats built the fossil stromatolites, and their oxygen eventually changed the atmosphere.Algae are eukaryotes, which arose much later (their chloroplasts are themselves derived from engulfed cyanobacteria). Mycoplasmas are wall-less parasitic bacteria that do not photosynthesise, and bryophytes are land plants, among the last of the four to appear.

Q: With passage of time, the molecular distance between organisms increases during evolution due to :

The molecular distance grows because of Neutral mutations.Kimura's neutral theory holds that most changes in DNA and protein sequences have no effect on fitness. Such neutral mutations are neither removed nor favoured by selection, so they accumulate at a roughly steady rate in separated lineages. The number of sequence differences therefore increases with time since divergence, which is the basis of the molecular clock.Drift is the process that fixes neutral mutations, but drift alone, without new mutations, cannot add differences. Point mutations include harmful ones that selection removes, so they do not accumulate in proportion to time.

Q: Ernst Myer was a proponent of :

Ernst Mayr (spelled Myer in the paper) proposed the Biological species concept.In 1942 Mayr defined species as groups of actually or potentially interbreeding natural populations that are reproductively isolated from other such groups. The definition rests on reproductive isolation rather than appearance.The phylogenetic species concept (Cracraft and others) defines species by shared derived characters and ancestry. The recognition concept (Paterson) rests on a shared mate-recognition system, and the evolutionary species concept is associated with Simpson and Wiley.

11.

Variation maintained in a population with Mendelian inheritance is explained by :

A.Natural selection theory
B.Blending inheritance theory
C.Hardy-Weinberg principle
D.Spontaneous generation theory

Exam Year(s)

MH SET - 2018, SET Exam - 2018,

Answer: C

It is explained by the Hardy-Weinberg principle.

Under Mendelian (particulate) inheritance, alleles pass unchanged from generation to generation. Hardy and Weinberg (1908) showed that, in a large randomly mating population without mutation, migration, selection or drift, allele and genotype frequencies stay constant (\(p^{2} + 2pq + q^{2} = 1\)), so variation is conserved rather than lost.

Blending inheritance would halve variation in every generation, which was a serious problem for Darwin's theory. Natural selection changes allele frequencies rather than preserving them, and spontaneous generation is a discredited idea about the origin of life.

Discuss in Forum

12.

Based on molecular evolution, which one of the following is close to humans ?

A.Orangutans
B.Gibbons
C.African apes
D.Lemur

Exam Year(s)

MH SET - 2018, SET Exam - 2018,

Answer: C

The closest to humans are the African apes.

DNA and protein comparisons show that humans are most closely related to the African apes, chimpanzees and bonobos above all, with whom we share about 98-99% of our DNA sequence, followed by gorillas. The human and chimpanzee lineages separated roughly 6-7 million years ago.

Orangutans, the Asian great apes, branched off earlier (about 13-16 million years ago), gibbons (the lesser apes) earlier still, and lemurs are prosimians, among the most distant primates from humans.

Discuss in Forum

13.

Which of the following statements is NOT true ?

A.Directional selection shifts the overall make up of the population by favouring variants of one extreme.
B.Stabilizing selection acts against extreme phenotypes.
C.In diversifying selection, no extreme phenotypes are favoured.
D.In stabilizing selection, genetic polymorphism is maintained.

Exam Year(s)

MH SET - 2018, SET Exam - 2018,

Answer: C

The statement that is NOT true is In diversifying selection, no extreme phenotypes are favoured.

Diversifying (disruptive) selection does the opposite: it favours both extremes of the range and acts against the intermediate forms, which can split a population into two distinct types.

The other statements follow the textbook account. Directional selection favours variants at one extreme and shifts the population mean that way. Stabilizing selection acts against both extremes and favours the average. And where the favoured intermediate is a heterozygote, as with the sickle-cell allele in malarial regions, selection for the middle keeps both alleles in the population, a balanced polymorphism. So the only statement that contradicts the definitions is the one about diversifying selection.

Discuss in Forum

14.

Which of the following is NOT a premating mechanism of isolation ?

A.Temporal isolation
B.Zygotic mortality
C.Behavioural isolation
D.Mechanical isolation

Exam Year(s)

MH SET - 2019, SET Exam - 2019,

Answer: B

The one that is not a premating mechanism is zygotic mortality.

Premating (prezygotic) barriers stop mating or fertilisation from happening: temporal isolation (breeding at different times), behavioural isolation (different courtship signals) and mechanical isolation (incompatible genitalia or flower structure).

Zygotic mortality acts after fertilisation, when the hybrid zygote or embryo dies, so it is a postmating (postzygotic) barrier, along with hybrid inviability and hybrid sterility.

Discuss in Forum

15.

A clade is a set of species :

A.Derived from a common ancestor
B.Derived from two ancestors
C.Derived from multiple ancestors
D.Inhabiting a particular environment

Exam Year(s)

MH SET - 2019, SET Exam - 2019,

Answer: A

A clade is a set of species derived from a common ancestor.

In cladistics a clade, or monophyletic group, consists of a single ancestor and all of its descendants; it is one complete branch of the tree of life. Birds, for example, form a clade within the dinosaurs.

A group derived from two or several unrelated ancestors would be polyphyletic, which cladistics rejects as a natural grouping. Species sharing a particular environment form an ecological group, not a clade.

Discuss in Forum

16.

The population of asiatic lion is small. Therefore, there is greater chance of :

A.Gene flow
B.Genetic drift
C.Mutation
D.Selection

Exam Year(s)

MH SET - 2019, SET Exam - 2019,

Answer: B

A small population has a greater chance of genetic drift.

Genetic drift is the random change in allele frequencies from one generation to the next due to chance in which individuals breed. Its effect is strongest in small populations, where alleles can be lost or fixed quickly. The Asiatic lions of Gir, descended from a very small number of survivors, show low genetic variation for this reason.

Gene flow needs migration between populations, the mutation rate does not depend on population size, and selection acts in populations of any size; only drift is specifically intensified by smallness.

Discuss in Forum

17.

During the evolution of life, the first formed cells were :

A.Photoautotrophs
B.Saprotrophs
C.Chemoautotrophs
D.Chemoheterotrophs

Exam Year(s)

MH SET - 2020, SET Exam - 2020,

Answer: D

The first cells were Chemoheterotrophs.

On the classical Oparin-Haldane account, which this question follows, the first cells arose in a 'primordial soup' rich in organic molecules made abiotically. They used those ready-made molecules as both energy and carbon source, anaerobically, which makes them chemoheterotrophs.

Photoautotrophs needed the more complex machinery of photosynthesis and came later. Saprotrophs feed on dead organisms, which could not exist before life did. Chemoautotrophs, which build organic matter from inorganic chemicals, are favoured by some newer theories but are not the textbook answer.

Discuss in Forum

18.

During the evolution of life, the first formed photosynthetic organisms were :

A.algae
B.cyanobacteria
C.mycoplasmas
D.bryophytes

Exam Year(s)

MH SET - 2020, SET Exam - 2020,

Answer: B

The first photosynthetic organisms among those listed were cyanobacteria.

Cyanobacteria are prokaryotes that carried out oxygen-releasing photosynthesis long before eukaryotes existed; their mats built the fossil stromatolites, and their oxygen eventually changed the atmosphere.

Algae are eukaryotes, which arose much later (their chloroplasts are themselves derived from engulfed cyanobacteria). Mycoplasmas are wall-less parasitic bacteria that do not photosynthesise, and bryophytes are land plants, among the last of the four to appear.

Discuss in Forum

19.

With passage of time, the molecular distance between organisms increases during evolution due to :

A.Random drift
B.Genetic drift
C.Neutral mutations
D.Point mutations

Exam Year(s)

MH SET - 2020, SET Exam - 2020,

Answer: C

The molecular distance grows because of Neutral mutations.

Kimura's neutral theory holds that most changes in DNA and protein sequences have no effect on fitness. Such neutral mutations are neither removed nor favoured by selection, so they accumulate at a roughly steady rate in separated lineages. The number of sequence differences therefore increases with time since divergence, which is the basis of the molecular clock.

Drift is the process that fixes neutral mutations, but drift alone, without new mutations, cannot add differences. Point mutations include harmful ones that selection removes, so they do not accumulate in proportion to time.

Discuss in Forum

20.

Ernst Myer was a proponent of :

A.Phylogenetic species concept
B.Biological species concept
C.Recognition species concept
D.Evolutionary species concept

Exam Year(s)

MH SET - 2020, SET Exam - 2020,

Answer: B

Ernst Mayr (spelled Myer in the paper) proposed the Biological species concept.

In 1942 Mayr defined species as groups of actually or potentially interbreeding natural populations that are reproductively isolated from other such groups. The definition rests on reproductive isolation rather than appearance.

The phylogenetic species concept (Cracraft and others) defines species by shared derived characters and ancestry. The recognition concept (Paterson) rests on a shared mate-recognition system, and the evolutionary species concept is associated with Simpson and Wiley.

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