Principles of Inheritance and Variation

• Reginald C. Punnett, the originator of the Punnett square.
• The four options differ only in his nationality and discipline.

The correct description of Punnett.

Every option carries the same name, so the question is entirely about two attributes: his nationality and his field. He was British, and he was a geneticist — a founder of modern genetics, and a collaborator of William Bateson, who coined the word “genetics”.

1. Two options say British and two do not, so nationality halves the field.
2. German is wrong, and Stanford is an American university, so those two go.
3. Of the two British options, one says zoologist and one says geneticist.
4. Punnett was a geneticist, so the last option is correct.

• Statement I about the 14 varieties Mendel selected.
• Statement II about his large sample size.

The truth of each statement.

Both statements are straight out of NCERT. Mendel studied seven contrasting characters, and each character needed two true-breeding varieties — one for each trait. Seven pairs is 14 varieties, which is exactly what statement I says. Statement II names one of the two things that made his conclusions trustworthy, the other being observation over several generations.

1. Mendel worked with seven pairs of contrasting characters — tall/dwarf, round/wrinkled, and so on.
2. Each pair needed two true-breeding lines, one showing each trait.
3. 7 × 2 = 14 varieties. Statement I is correct.
4. Statement II: Mendel counted thousands of plants, and that large sample is precisely what raised his work above anecdote. Correct.
5. Both statements stand.

• Tt × tt, a test cross.
• 100 offspring in total.

How many are tt, Tt and TT.

The dwarf parent is tt and can only ever give a t. So every single offspring receives a t from that side, and no offspring can possibly be TT — there is no second T available anywhere in the cross. The Tt parent supplies T or t equally, which splits the offspring evenly into Tt and tt.

1. The tt parent produces only t gametes.
2. The Tt parent produces T and t gametes in equal numbers.
3. Combining: T × t gives Tt, and t × t gives tt.
4. So the offspring are 50%% Tt and 50%% tt.
5. Of 100 offspring: 50 tt, 50 Tt, and 0 TT. TT is impossible because only one parent carries a T at all.

• Four stated reasons for choosing the garden pea.

Which reasons are correct.

All four are genuine, and each solves a different practical problem. (a) gives control — self-pollination keeps lines pure, while hand cross-pollination lets him make the crosses he wants. (b) gives clear data — traits that are either one thing or the other, with no middle ground to argue about. (c) gives numbers — large samples in a small garden. (d) gives generations — results within a season rather than a lifetime.

1. (a) Peas self-pollinate naturally, which maintains true-breeding lines without effort, and the flower structure still allows deliberate crossing. Correct.
2. (b) Seven characters each appear in two sharply distinct forms — no blending, no judgement calls. Correct.
3. (c) A small plant means many individuals in a monastery garden, which is what made his large sample possible. Correct.
4. (d) A short life cycle meant he could follow F₁, F₂ and beyond within a few years. Correct.
5. All four stand.

• Four candidate features of Mendel's approach.

Which approach established his results as general rules.

Two things together made his results convincing, and NCERT names them as a pair: a large sample size, which rules out coincidence, and observation over several generations, which shows the pattern repeats rather than being a one-off. Either alone is weaker than both together, and the option list is built so that one option contains both.

1. A large sample means the ratios are statistically reliable rather than accidental.
2. Repeating across generations shows the same ratios reappear predictably.
3. Options 1 and 2 each name one of these, so each is true but incomplete.
4. Option 4 names both, and is therefore the fullest answer.
5. Option 3 mentions statistical analysis, which Mendel did use — but it is a consequence of having large samples, not the approach itself, and it is not the phrase NCERT uses here.

• Four things a Punnett square might show.

Which of them it can show.

A Punnett square is built from the gametes — they are the row and column headings — and the boxes inside are the genotypes of the zygotes. So (i) and (ii) are not merely visible in it, they are its two structural halves. Run the square a second time on the F₁ and you get the F₂ genotypes too, and reading dominance off those genotypes gives the phenotypes. All four.

1. (i) The headings along the top and side are the gamete types. You cannot draw the square without identifying them. Yes.
2. (ii) Each box holds the genotype of a possible zygote. That is what the square is for. Yes.
3. (iii) One square gives F₁; selfing the F₁ and drawing a second square gives F₂. Yes.
4. (iv) Apply the dominance relationship to each genotype and the phenotypes follow immediately. Yes.
5. All four.

• Four statements about alleles, genes and Mendel's laws.

Which statements are correct.

Statements I, II and IV are all standard. Statement III is the planted one: Mendel's work did provide evidence for discrete hereditary units. That is precisely what the reappearance of the recessive trait in F₂ demonstrates — something particulate was passed on intact rather than being diluted away. He called them factors; we call them genes.

1. I. Alleles do not blend — the recessive trait returns intact in F₂. Correct.
2. II. Alleles are alternative forms of the same gene, differing slightly. Correct.
3. III. Mendel's results are precisely the evidence that discrete hereditary units exist. Incorrect.
4. IV. The law of independent assortment states that different gene pairs segregate independently. Correct.
5. So I, II and IV.