Q.What do you understand by a gene pool?
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🔒 Start your 14-day free trial to unlock the full solution →Concept understanding — Biological Species Concept
Imagine you see a lion and a tiger in a zoo. They look different, they sound different, and they never produce cubs together in the wild. Now imagine a Labrador and a Poodle — they look quite different too, but they can mate and have puppies that grow up to have their own puppies. What makes the first pair "different species" and the second pair "the same species"? That is exactly the question the Biological Species Concept tries to answer.
At its simplest, this concept says: a species is a group of actually or potentially interbreeding natural populations that are reproductively isolated from other such groups. Let's unpack that.
The core idea is not about how similar two organisms look. It is about whether they can exchange genes in nature. If two organisms can mate and produce fertile offspring under natural conditions, they belong to the same species. If they cannot — because their mating seasons don't match, their reproductive organs are incompatible, or their offspring are sterile — they belong to different species.
The key phrase is "in nature." A lion and a tiger can sometimes be forced to mate in captivity and produce a "liger," but that liger is almost always sterile. More importantly, lions and tigers never interbreed in the wild. So they remain separate species under this concept.
This concept was championed by the evolutionary biologist Ernst Mayr and is the most widely used definition in NCERT textbooks for Class 12 Biology. It is the standard you will encounter in exams.
Why does this matter? Because it gives us a clear, testable criterion. Instead of arguing about how different two animals look, we can ask a practical question: do they interbreed in nature? This is especially useful for classifying closely related organisms that look very similar but are reproductively isolated.
However, this concept has important limitations — and NCERT expects you to know them:
- It only works for organisms that reproduce sexually. It is useless for bacteria, many protists, and fungi that reproduce asexually.
- It cannot be applied to fossils. You cannot observe the mating behaviour of a dinosaur.
- It fails for plants that frequently hybridise in nature (like many oak species) yet remain distinct.
- It cannot handle populations that are geographically separated (allopatric) — we cannot test if two groups of squirrels on different continents would interbreed if they ever met. …
A gene pool is the sum of all genes and alleles in a population; evolution is a change in its allele frequencies.
A gene pool is the complete set of all the genes, together with all of their alleles, present in all the reproducing members of a population at a particular time. Each allele occurs in the pool at a certain frequency (its allele frequency).
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- CBSE 2025Set F1 markMCQQ.Which of the following is an important factor in the formation of new species?(a) Isolation(b) Mutation(c) Variation(d) Competition
›Reveal solutionSolution
Isolation (reproductive/geographic) is the crucial factor that lets populations diverge into separate species.
Speciation is the formation of new species. Variation and mutation supply the raw genetic differences, and natural selection acts on them, but a population cannot become a distinct species while it freely interbreeds with the parent population, because gene flow keeps the gene pools mixed. Isolation — a barrier to reproduction (geographic separation or reproductive isolating mechanisms) — stops this gene flow. Once isolated, th …
- CBSE 2021Set D1 markMCQQ.Which of the following factors is important in the formation of new species ?(a) Competition(b) Mutation(c) Isolation(d) Continuous variation
›Reveal solutionSolution
Isolation is essential for the formation of new species.
Speciation requires that two populations be prevented from interbreeding so that their gene pools diverge. Isolation — geographical (a physical barrier) or reproductive — stops gene flow between them, allowing mutations, variations and natural selection to accumulate independently in each group until they can no longer interbreed, forming distinct species. Although mutation suppli …
- CBSE 2019Set HE1 markQ.Fill in the blank: Morphologically and genetically similar individuals are called ______.
›Reveal solutionSolution
A species is the basic unit of classification — a group of morphologically and genetically similar individuals that can interbreed and produce fertile offspring.
In taxonomy, a species is defined as a group of natural populations whose members are morphologically (structurally) and genetically similar to one another, share a common gene pool, and are capable of interbreeding to produce fertile offspring. Members of a species are reproductively isolated from members of other species — meaning they normally cannot interbreed with them, or if they do, the offspring is not fertile (e.g., a mule from ho …
- CBSE 2019Set ANNUAL1 markQ.Give an example for an inter-specific hybrid animal.
›Reveal solutionSolution
A classic interspecific hybrid animal is the mule.
Concept: Interspecific hybridisation is the crossing of two different (but related) species. The offspring — an interspecific hybrid — often combines desirable traits of both parents but is usually sterile because the two parental chromosome sets do not pair properly during meiosis (an example of post-zygotic reproductive isolation). The best-known exampl …
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