In-text Questions — Variation — Heredity

1. 12 marksNCERT Cl-10 Science, In-text Qs after §8.1, Q1

   If a trait A exists in 10% of a population of an asexually reproducing species and a trait B exists in 60% of the same population, which trait is likely to have arisen earlier?

   Hint. In an asexually reproducing population, a variation spreads only by being passed down through more and more generations of descendants — think about which trait has had more time to do that.

   Step 1 — Recall how variation spreads in asexual reproduction. A new variation appears in one individual and is then passed down only to its own descendants, spreading through the population only as more generations pass.

   Step 2 — Compare the two traits' current spread. Trait B is present in 60% of the population, far more than trait A's 10%.

   Step 3 — Connect spread to time. Since a trait needs more generations (more time) to spread to a larger share of the population, the trait with the wider spread today has likely had more time to do so.

   ✦ Answer: Trait B is likely to have arisen earlier, since its much wider presence in the population (60% vs 10%) suggests it has had more generations to spread.

   Where students slip. Assuming the rarer trait (A) must be older 'because it's more special or refined' — spread within an asexual population tracks time elapsed, not any notion of sophistication, so the more common trait is the one with the longer history.

2. 22 marksNCERT Cl-10 Science, In-text Qs after §8.1, Q2

   How does the creation of variations in a species promote survival?

   Hint. Think about what happens to a population with no variation at all when the environment suddenly changes, versus one with many different variants already present.

   Step 1 — Recall what variation means for a population. Variation means individuals within a population differ from each other in various ways, rather than all being identical.

   Step 2 — Consider an environmental change. If the environment changes drastically (e.g. a sudden rise in temperature), individuals with characteristics unsuited to the new conditions may die out.

   Step 3 — Explain why variation helps here. Since some variants may already happen to have characteristics suited to the new conditions, they are more likely to survive and continue the population, even though the population as a whole wasn't 'prepared' for this specific change.

   ✦ Answer: Variation means a population already contains many different individuals; if the environment changes drastically, at least some of these variants are likely to be suited to the new conditions and survive, keeping the species going even though the change was unpredictable.

   Where students slip. Saying variation helps because it makes 'each individual stronger' — the benefit is at the population level: having many different variants increases the odds that some survive an unpredictable change, not that every individual is generally superior.

Solutions written by the tuition.in editorial team and checked against the NCERT Class 10 Science textbook, Reprint 2026-27 (jesc108.pdf) — a 6-page chapter with two in-text question sets (6 questions total) plus one end-of-chapter Exercise (4 questions, not 12 — a stale figure carried over from the old combined 'Heredity and Evolution' chapter). The Evolution half is gone entirely, and the chapter never uses 'allele', 'genotype', 'phenotype', 'Punnett square', or the formal law names — it teaches through Mendel's own TT/Tt/tt notation and narrative.. Questions are referenced from the NCERT textbook for identification.