Gregor Mendel conducted hybridisation experiments in garden pea for seven years and proposed the law of inheri

Question

Q. Gregor Mendel conducted hybridisation experiments in garden pea for seven years and proposed the law of inheritance.

(a) Why was he successful in his hybridisation experiments ? Give two reasons.

(b) State the law of independent assortment as proposed by Mendel after his dihybrid crosses.

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Concept understanding — Mendel's Experimental Design

Let’s begin with something you already know from everyday life. Suppose you mix red and white paint — you get pink. Now imagine you cross a tall pea plant with a short one. Common sense might say you’ll get a medium-sized plant. But Mendel found that you don’t. You get all tall plants in the first generation, and then in the next generation, short plants reappear as if they had never been mixed. That is the puzzle Mendel set out to solve, and his experimental design was the tool that cracked it.

The core idea: controlled, large-scale, and trait-by-trait

Mendel’s experimental design was not just “grow some peas and see what happens.” It was a carefully planned method that had three key features:

He chose a single trait at a time — for example, only seed shape (round vs wrinkled), not seed shape plus flower colour plus plant height all at once. This kept the results clear and interpretable.
He used pure-breeding lines — plants that, when self-pollinated, always produced offspring identical to themselves for that trait. A pure round-seeded plant always gave round seeds; a pure wrinkled-seeded plant always gave wrinkled seeds. This gave him a known starting point.
He counted large numbers — not just a handful of plants, but hundreds or thousands. This allowed patterns to emerge that would be invisible in small samples.

Important

Mendel’s genius was not in discovering that traits are inherited — farmers knew that. His breakthrough was in designing an experiment that could reveal the rules of inheritance by controlling variables, using pure lines, and counting systematically. This is why he is called the father of genetics.

The step-by-step plan Mendel followed

Mendel worked with the garden pea (Pisum sativum) for practical reasons: it was easy to grow, had a short generation time, and — crucially — its flowers normally self-pollinate, so he could control exactly which plants were crossed.

His typical experiment went like this:

Take two pure-breeding parents that differ in one trait — say, a pure tall plant and a pure short plant. These are the P generation (parental generation).
Cross them artificially — he removed the male parts (anthers) from one flower and dusted pollen from the other parent onto its stigma. This ensured no accidental self-pollination.
Grow the offspring — these are the F₁ generation (first filial generation). He observed that all F₁ plants were tall. The short trait had vanished.
Let the F₁ plants self-pollinate — he did not cross them again; he simply let them produce seeds on their own. These seeds grew into the F₂ generation (second filial generation).
Count and record — in the F₂ generation, both tall and short plants appeared, in a ratio of roughly three tall to one short. The short trait had reappeared.

He repeated this exact procedure for each of the seven traits he studied — seed shape, seed colour, flower colour, pod shape, pod colour, flower position, and stem height. Every time, the pattern was the same: one trait dominated in F₁, and both traits reappeared in a 3:1 ratio in F₂.

Why this design was revolutionary

Before Mendel, people believed in blending inheritance — the idea that parental traits mix like paint. Mendel’s design proved that inheritance is particulate: traits are carried by discrete units (what we now call genes) that remain intact across generations. The short trait did not disappear; it was merely hidden in the F₁ plants and reappeared unchanged in F₂.

Note

The NCERT textbook emphasises that Mendel’s success came from his scientific approach: he chose the right organism, studied one trait at a time, kept accurate records, and used mathematics to analyse his results. This was completely new for biology in the 1860s.

A few key terms you will encounter …

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Mendel's success stemmed from his meticulous experimental design using the garden pea plant and his quantitative analysis of distinct, contrasting traits, leading to the Law of Independent Assortment which states that alleles for different traits segregate independently during gamete formation.

Gregor Mendel's groundbreaking work on inheritance, conducted over seven years with the garden pea plant (Pisum sativum), laid the foundation for modern genetics. His success was not merely a stroke of luck but a testament to his meticulous experimental design and analytical approach, which allowed him to discern patterns of inheritance that had eluded scientists before him.

(a) Why was he successful in his hybridisation experiments?

Mendel's success can be attributed to several key factors, primarily his judicious choice of the experimental organism and his rigorous, quantitative methodology.

Choice of Garden Pea Plant (Pisum sativum):

Mendel's selection of the garden pea was crucial. This plant offered several advantages that made it an ideal subject for studying inheritance:
- Distinct, Contrasting Characters: Pea plants exhibit several easily observable, clear-cut contrasting traits, such as tall/dwarf stem height, round/wrinkled seed shape, yellow/green seed colour, and purple/white flower colour. These distinct alternatives made it straightforward to categorize and count offspring.
- Short Life Cycle: Pea plants have a relatively short generation time, allowing Mendel to study multiple generations within a reasonable period.
- Easy Cultivation: They are easy to grow and maintain in large numbers, providing ample data for statistical analysis.
- Self-Pollination and Easy Cross-Pollination: Pea flowers are bisexual and naturally self-pollinating, ensuring pure lines (homozygous parents) could be maintained. Crucially, they could also be easily cross-pollinated artificially by removing the anthers (emasculation) and dusting pollen from another plant, allowing Mendel to control the crosses precisely.
Important

The presence of distinct, contrasting characters and the ability to easily control pollination were paramount to Mendel's ability to track inheritance patterns accurately.
Meticulous Experimental Design and Quantitative Analysis:

Beyond the plant itself, Mendel's approach to experimentation was revolutionary.
- Focus on One or a Few Traits at a Time: Unlike previous breeders who observed overall resemblances, Mendel focused on the inheritance of one or two characters at a time. This simplified the analysis and allowed him to identify specific patterns for each trait.
- Use of Pure Breeding Lines: He started his experiments with pure-breeding (true-breeding) lines for each trait, meaning plants that consistently produced offspring with the same trait over several generations through self-pollination. This ensured that the parental generation was homozygous for the traits being studied.
- Large Sample Sizes: Mendel conducted his experiments with a large number of plants and observed thousands of offspring. This provided statistically significant data, reducing the impact of random variations and allowing him to identify consistent ratios in the progeny.
- Statistical Analysis of Results: He meticulously counted and recorded the number of offspring exhibiting each trait in every generation. He then applied mathematical and statistical reasoning to analyze these numerical data, which allowed him to deduce the underlying principles of inheritance, such as the 3:1 ratio in the F2 generation of monohybrid crosses. This quantitative approach was a significant departure from the qualitative observations of his predecessors. …

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Same / Similar Concept — real previous-year questions on the same or a closely similar concept, not this exact question.

CBSE 2026Set EG1 markMCQ
$Q. How many years did Gregor Mendel conduct experiment on plants of garden pea?$
(a) Five years
(b) Two years
(c) Seven years
(d) Eleven years
›Reveal solutionSolution

Mendel conducted his hybridisation experiments on garden pea for about seven years — option (c).

Gregor Johann Mendel carried out his classic breeding experiments on the garden pea, Pisum sativum, in the monastery garden at Brno over roughly seven years (1856–1863). He chose pea because it has clear contrasting traits, is normally self-pollinating, has a short life cycle and is easy to hybridise. From these …

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$Q. What is the cross called, when a dominant phenotype plant is crossed with the recessive parent plant instead of self-crossing?$
›Reveal solutionSolution

The cross of a dominant-phenotype individual with the homozygous recessive parent is a test cross.

Concept: A dominant phenotype can be produced by either a homozygous (TT) or a heterozygous (Tt) genotype, which cannot be told apart by appearance. …

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$Q. Which of the following claims would be accurate if garden pea plants from Mendel's Garden were sampled ?$
(a) Round seeds were more prevalent than wrinkled seeds
(b) Wrinkled seeds were more prevalent than round seeds
(c) Both round and wrinkled seeds were equally prevalent
(d) The response depended on the time of day the sample was taken
›Reveal solutionSolution

In Mendel's monohybrid cross, round (dominant) seeds outnumbered wrinkled (recessive) seeds roughly 3:1 in the F2 generation.

Mendel crossed true-breeding round-seeded pea plants with true-breeding wrinkled-seeded plants. The F1 generation was entirely round-seeded (round being the dominant trait), and when F1 plants were self-pollinated, the F2 generation segregated in an approximate 3:1 ratio of round to wrinkled seeds (Mendel actually recorded 5474 round : 1850 wrinkled, very close to 3:1). So if a sample were drawn from Mendel's garden pea plants (a mixed population across generations, dom …

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CBSE 2024Set BOTANY1 markMCQ
$Q. Fill in the blank selecting the appropriate alternative: Out of seven pairs of contrasting characters of pea plant used by Mendel, ____ had dominant green and recessive yellow.$
(i) flower colour
(ii) pod colour
(iii) seed colour
(iv) stem colour
›Reveal solutionSolution

Pod colour is the trait among Mendel's seven where green is dominant and yellow is recessive.

Mendel studied seven pairs of contrasting characters in garden pea (Pisum sativum): seed shape (round dominant/wrinkled recessive), seed colour (yellow dominant/green recessive), flower colour (violet dominant/white recessive), pod shape (inflated dominant/constricted recessive), pod colour (green dominant/yellow recessive), flower position (axial dominant/terminal recessive), and stem height (t …

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CBSE 2023Set A1 mark
$Q. Fill in the blank: ______ conducted hybridization experiments on garden peas for seven years.$
›Reveal solutionSolution

Mendel, an Austrian monk, performed pea (Pisum sativum) hybridisation experiments at the monastery in Brno and laid the foundation of genetics.

Gregor Johann Mendel chose the garden pea plant for his experiments because it had several contrasting, easily distinguishable traits (like round/wrinkled seeds, tall/dwarf plants), was self-pollinating (allowing pure-line breeding) but could also be cross-pollinated artificially, and had a short generation time. Over seven years of carefully planned cro …

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CBSE 2022Set GO1 mark
$Q. How many pairs of contrasting traits were studied by Mendel in pea plant?$
›Reveal solutionSolution
Mendel selected 7 pairs of contrasting characters in pea.

Concept. For his hybridisation experiments Mendel chose the garden pea and worked with seven pairs of contrasting (alternative) traits, each showing a clear dominant and recessive form:

Seed shape — round / wrinkled

Seed (cotyledon) colour — yellow / green

Flower colour — violet / white …
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CBSE 2018Set ANNUAL1 markMCQ
$Q. How many pairs of contrasting characters were studied by Mendel?$
(a) 5 pairs
(b) 6 pairs
(c) 7 pairs
(d) 8 pairs
›Reveal solutionSolution

Mendel selected seven distinct, easily distinguishable contrasting character-pairs in the garden pea for his hybridisation experiments.

Gregor Mendel conducted his classic breeding experiments on the garden pea (Pisum sativum) because it is self-pollinating, easy to cross-pollinate artificially, and has several traits with clear-cut contrasting (either/or) forms. He specifically chose and studied seven pairs of contrasting characters: (1) seed shape - round/wrinkled, (2) seed colour - yellow/green, (3) pod shape - inflated/constricted, (4) pod colour - green/yellow, (5) flower colour - violet/white, (6) flower position - axial/terminal, and (7) s …

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CBSE 2018Set ANNUAL1 mark
$Q. Why is self pollination procedure essential among the different progeny hybrids for the selection of new recombinants in plant breeding programme?$
›Reveal solutionSolution

Repeated self-pollination of hybrid progeny fixes new gene combinations into a stable, true-breeding (homozygous) form, which is essential before a useful recombinant variety can be released.

In a plant breeding programme, after two parent varieties are crossed to produce hybrid progeny showing new combinations of desirable traits (recombinants), these progeny are still heterozygous and will continue to segregate/throw a mixture of different genotypes in subsequent generations if allowed to cross-pollinate freely. To 'fix' the desired new trait combination into a stable, uniform, true-breeding variety, breeders subject the selected progeny to repeated cycles of self-pollination across several successive generations. Self-pollination increases homozygosity generation after generation, so that eventually a line is …

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$Q. Write the answer in one word/sentence: Write botanical name of maize.$
›Reveal solutionSolution

The botanical name of maize is Zea mays.

Maize, commonly called corn, is a monocot cereal crop belonging to the grass family (Poaceae). Its scientific binomial name, following Linnaeus' system of nomenclature, is Zea mays, where Zea is …

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CBSE 2017Set ANNUAL1 markMCQ
$Q. Which one of the following trait of pea plant studied by Mendel is dominant?$
(a) Green pod colour
(b) Yellow pod colour
(c) White flower colour
(d) Terminal flower position
›Reveal solutionSolution

Of Mendel's seven pea traits, green pod colour is dominant over yellow.

Mendel studied seven contrasting traits in garden pea (Pisum sativum), each with a dominant and a recessive form:

Trait Dominant Recessive
Pod colour Green Yellow
Flower colour Violet White
Flower position Axial Terminal
Stem height Tall Dwarf
…

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Trait	Dominant	Recessive
Pod colour	Green	Yellow
Flower colour	Violet	White
Flower position	Axial	Terminal
Stem height	Tall	Dwarf
…

Q.Gregor Mendel conducted hybridisation experiments in garden pea for seven years and proposed the law of inheritance.

(a) Why was he successful in his hybridisation experiments?

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