A person has to perform crosses for the purpose of studying inheritance of a few traits / characters. What sho

NCERT Exemplar · Q22

Q. A person has to perform crosses for the purpose of studying inheritance of a few traits / characters. What should be the criteria for selecting the organisms?

Odisha ChseShort· 2mImportance★★★★★

45% · 38/85 Questions

🔒 Locked · start free trial →

You're viewing a preview — the full solution, concept, methods & PYQ mapping are locked.

Start your 14-day free trial to unlock the full solution →

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 …

Start your 14-day free trial to unlock the full solution →

Organisms for studying inheritance should have a short life cycle, produce many offspring, exhibit clear contrasting traits, and be easy to cultivate and cross-breed.

When embarking on the study of inheritance, the choice of organism is perhaps the most critical initial decision, directly impacting the feasibility and success of the experiment. Just as Gregor Mendel meticulously selected the garden pea plant (Pisum sativum) for his groundbreaking work, any researcher aiming to understand how traits pass from one generation to the next must consider specific biological and practical criteria. The goal is to find an organism that allows for clear observation, controlled experimentation, and rapid data collection.

Here are the key criteria for selecting organisms for genetic crosses:

Short Life Cycle: An organism with a short life cycle is highly advantageous because it allows for the study of multiple generations within a relatively short period. If an organism takes years to mature and reproduce, an inheritance study spanning several generations would become impractically long. Pea plants, for instance, complete their life cycle in a single growing season, enabling Mendel to observe many generations quickly.
Production of a Large Number of Offspring: To accurately determine inheritance patterns and ratios, a large sample size is essential. Organisms that produce numerous offspring per cross provide sufficient data for statistical analysis, making the observed ratios of traits more reliable and less prone to random fluctuations. This helps in identifying the underlying genetic principles with greater confidence.
Possession of Easily Observable Contrasting Characters: The traits chosen for study must be distinct and clearly distinguishable from one another. Ambiguous or continuously varying traits make it difficult to categorize offspring and track inheritance patterns. Mendel's success was partly due to his focus on seven pairs of contrasting characters in pea plants, such as tall/dwarf stem height, round/wrinkled seed shape, and green/yellow pod colour, which showed clear-cut differences.

Note

These contrasting characters should ideally be controlled by single genes, making their inheritance patterns simpler to decipher without the complexities of polygenic inheritance initially.
Ease of Cultivation and Handling: The chosen organism should be relatively easy to grow, maintain, and manipulate in an experimental setting. This includes factors like space requirements, nutritional needs, resistance to common diseases, and the simplicity of performing crosses. Difficult-to-handle organisms can introduce experimental errors or make large-scale studies impractical. …

Start your 14-day free trial to unlock the full solution →

←Previous questionQ21 — Enlist the steps of controlled cross pollination. Would emasculation b…→Next questionQ23 — The pedigree chart given below shows a particular trait which is absen…

Q.A person has to perform crosses for the purpose of studying inheritance of a few traits / characters. What should be the criteria for selecting the organisms?

🎓Unlock everything free for 14 days

Unlock everything free for 14 days