Heredity & Genetics — REET Notes
This page covers the core ideas of heredity for REET Level 2 (Maths-Science) — Mendel's laws, basic genetics vocabulary, and disease-resistant crop varieties. REET 2024 asked direct questions on disease-resistant varieties developed through plant breeding, so this page explains both classical heredity and practical agricultural genetics with simple examples, keeping classroom teaching for grades 6-8 in mind as well.
- 2 questions in REET 2024
- Class 6-8 level
- 9 min read
How this topic is asked in REET
In REET 2024, both questions on this topic were based on disease-resistant crop varieties developed through plant breeding — the mustard variety 'Pusa Swarnim' was described as resistant to white rust disease, and the wheat variety 'Himgiri' as resistant to hill bunt disease. In other words, REET does not limit heredity to Mendel's theoretical laws alone — it also tests the practical application of genetics in agriculture (improved varieties), so you need to prepare both sides.
What Is Heredity
Heredity is the process by which physical and other traits of parents are passed on to their offspring. These traits travel from one generation to the next through genes. The scientific study of heredity is called genetics. In simple terms, heredity is the reason children resemble their parents in features such as height or eye colour, because the genes carrying these traits are copied and passed down from parent to offspring during reproduction.
The Austrian scientist Gregor Johann Mendel is called the 'father of genetics.' He experimented on pea plants (Pisum sativum) for years — pea was chosen because it shows clearly contrasting pairs of traits (such as tall/dwarf plant, round/wrinkled seed, purple/white flower) and can be grown through several generations quickly. Mendel published his findings in 1866, though they only received scientific recognition after 1900, when three other scientists independently obtained similar results and rediscovered Mendel's work. Because the pea plant's traits were so clearly either one form or the other, with no in-between blending, Mendel could count exactly how many offspring showed each trait across generations and work out the mathematical ratios that became the basis of his laws.
Mendel's Laws of Heredity
| Law | Meaning |
|---|---|
| Law of Dominance | When two contrasting forms of a trait (such as tall and dwarf) are present together, one form (dominant) appears in the offspring and the other (recessive) is suppressed |
| Law of Segregation | During gamete formation, the two alleles of a gene pair for a trait separate from each other and go into different gametes |
| Law of Independent Assortment | When two or more different traits (such as seed colour and shape) are studied together, the inheritance of each trait is independent of the other |
Basic Genetics Vocabulary
- Gene
- The genetic unit that controls a trait
- Allele
- The two alternative forms of the same gene (such as the tall and dwarf alleles for height)
- Dominant trait
- The trait that appears in the offspring (F1)
- Recessive trait
- The trait that stays suppressed and hidden when present along with the dominant trait
- Genotype
- The genetic (gene) make-up of an organism
- Phenotype
- The visible, outward traits of an organism
- Homozygous
- When both alleles of a trait are identical
- Heterozygous
- When both alleles of a trait are different
Sex Determination in Humans
Every human cell has 23 pairs of chromosomes, one of which is called the sex chromosome pair. A female has two identical sex chromosomes (XX), while a male has two different sex chromosomes (XY). The sex of the offspring depends on whether an X or a Y chromosome is inherited from the father — the mother always contributes an X. Since the mother's contribution stays fixed at X, it is entirely the father's X or Y chromosome that decides whether the child develops as XX (female) or XY (male). Every human cell carries 23 pairs of chromosomes in total, and it is only this one pair — the sex chromosomes — that differs between a male and a female, since a female carries two X chromosomes (XX) and a male carries one X and one Y (XY).
Why Variation Matters
During reproduction, some variation arises between offspring and their parents, so all organisms of the same species are not exactly identical. This variation helps organisms survive and adapt in a changing environment — if all organisms were exactly alike, an entire species could be wiped out at once by an unfavourable condition (such as a new disease). For this reason, variation is considered a basic requirement of evolution, and the same principle is used in plant breeding, where scientists select a desired trait (such as disease resistance) from among different varieties to develop better ones. This same idea connects directly to the disease-resistant crop varieties described below — plant breeders are essentially drawing on natural variation among different plants to pick out and multiply the specific traits, such as disease resistance, that help a crop survive better.
Disease-Resistant Crop Varieties Developed Through Plant Breeding
| Crop | Variety | Resistant Disease |
|---|---|---|
| Mustard | Pusa Swarnim | White rust |
| Wheat | Himgiri | Leaf rust and hill bunt |
In plant breeding, hybridisation and selection are used to develop varieties that resist pests and diseases, survive on less water, and still give a higher yield.
How to Teach This in Class
Classroom activity
Have students count one visible trait among classmates (such as attached vs. free earlobes) and build a simple chart from it — this makes the idea of dominant and recessive traits click with a real, first-hand example.
Teaching aid
Show pictures of tall/dwarf pea plants or green/yellow seeds to explain Mendel's experiment through simple visuals.
Common misconception
Students often assume that parents' traits 'blend' together in the offspring. Clarify that traits do not blend — only the dominant trait shows up, while the recessive trait stays hidden and can reappear in a later generation. This connects directly to Mendel's Law of Dominance — of the two contrasting forms of a trait, one is expressed while the other is suppressed but not lost, which is why a recessive trait that skips a generation can resurface later, if both parents happen to be carrying the same hidden recessive allele.
Assessment idea
Ask students whether two brown-eyed (dominant) parents will always have brown-eyed children — this checks a deeper understanding of dominant-recessive traits, since both parents may be carrying a hidden recessive allele that can show up in the child. A useful follow-up question is what this means for the child's genotype versus phenotype — the child's visible phenotype may be brown eyes even though the underlying genotype carries one hidden recessive allele inherited from each parent.
Memory trick
Remember Mendel's three laws with 'D-S-I' — Dominance, Segregation, Independent assortment. Keep the first letters D, S, I in that order and you'll never mix up the three laws.
Questions Asked in REET 2024 (With Solutions)
Question 124
The variety of Brassica, resistance to “White rust” disease is
- Aपूसा कोमल
- Bपूसा शुभ्रा
- Cपूसा सदाबहार
- Dपूसा स्वर्णिम
Explanation
पादप प्रजनन (plant breeding) द्वारा विकसित रोग-प्रतिरोधी किस्मों में सरसों (Brassica, करन राई) की किस्म पूसा स्वर्णिम श्वेत किट्ट (white rust) रोग के प्रति प्रतिरोधी है। पूसा कोमल लोबिया की (बैक्टीरियल ब्लाइट प्रतिरोधी), पूसा शुभ्रा फूलगोभी की और पूसा सदाबहार मिर्च की किस्म है।
Question 138
The variety of wheat, resistance to Hillbunt disease is
- Aपूसा शुभ्रा
- Bआई आर आर आई
- Cपूसा सदाबहार
- Dहिमगिरी
Explanation
NCERT (कक्षा 9, खाद्य संसाधनों में सुधार) के अनुसार गेहूँ की किस्म 'हिमगिरी' पत्तियों के रतुआ (leaf rust) और हिल बंट रोग के प्रति प्रतिरोधी है। पूसा शुभ्रा फूलगोभी की और पूसा सदाबहार मिर्च की किस्म है, जबकि IRRI अंतरराष्ट्रीय चावल अनुसंधान संस्थान का नाम है।
Practice Questions
Question 1
Who is called the 'Father of Genetics'?
- Aचार्ल्स डार्विन
- Bग्रेगर मेंडल
- Cलुई पाश्चर
- Dरॉबर्ट हुक
Explanation
Gregor Mendel experimented on pea plants and gave the laws of heredity, which is why he is called the father of genetics.
Question 2
Which plant did Mendel mainly choose for his experiments?
- Aगेहूँ
- Bमटर
- Cधान
- Dसरसों
Explanation
Pea plants show clearly contrasting pairs of traits and can be grown through several generations quickly, which is why Mendel chose them for his experiments.
Question 3
When a trait appears in the offspring and suppresses the other trait, the trait that appears is called —
- Aअप्रभावी (recessive)
- Bप्रभावी (dominant)
- Cउत्परिवर्ती
- Dसंकर
Explanation
The trait that appears in the offspring (F1) and suppresses the other trait is called the dominant trait.
Question 4
The genetic (gene) makeup of an organism is called —
- Aफीनोटाइप
- Bजीनोटाइप
- Cहोमोजाइगस
- Dएलील
Explanation
The genetic make-up of an organism is called its genotype, while its outward visible traits are called its phenotype.
Question 5
According to which of Mendel's laws do the two alleles of a gene pair separate during gamete formation?
- Aप्रभाविता का नियम
- Bपृथक्करण का नियम
- Cस्वतंत्र अपव्यूहन का नियम
- Dउत्परिवर्तन का नियम
Explanation
According to the Law of Segregation, the two alleles of a gene pair separate and go into different gametes when gametes are formed.
Question 6
The determination of a child's sex in humans mainly depends on —
- Aमाता से मिलने वाला गुणसूत्र
- Bपिता से मिलने वाला X या Y गुणसूत्र
- Cसंतान की आयु
- Dवातावरण
Explanation
The mother always contributes an X chromosome; whichever chromosome — X or Y — is inherited from the father decides the sex of the child.
Question 7
Which variety of mustard has been developed to be resistant to white rust disease?
- Aपूसा कोमल
- Bहिमगिरी
- Cपूसा स्वर्णिम
- Dपूसा शुभ्रा
Explanation
The mustard variety Pusa Swarnim was developed through plant breeding to be resistant to white rust disease.
Question 8
The most suitable activity to introduce heredity simply in class is —
- Aसीधे जटिल आनुवंशिक समीकरण पढ़ाना
- Bमाता-पिता व बच्चों के किसी दृश्य गुण (जैसे आँखों का रंग) का उदाहरण देना
- Cविषय को कक्षा 6-8 में न पढ़ाना
- Dकेवल परिभाषा रटवाना
Explanation
Using a familiar everyday example (such as eye colour in parents and children) to explain a complex idea in simple terms is the most effective approach at the class 6-8 level.
Question 9
A common misconception among students is that parents' traits 'blend' in the offspring. The correct clarification is —
- Aयह सही है, गुण हमेशा मिश्रित होते हैं
- Bगुण मिश्रित नहीं होते; प्रभावी गुण प्रकट होता है, अप्रभावी छिपा रहता है
- Cकेवल माता के गुण प्रकट होते हैं
- Dकेवल पिता के गुण प्रकट होते हैं
Explanation
According to Mendel's Law of Dominance, traits do not blend; the dominant trait appears while the recessive trait stays hidden and can reappear in the next generation.
Question 10
The principle that the inheritance of two different traits (like seed colour and shape) is independent of each other is called —
- Aप्रभाविता का नियम
- Bपृथक्करण का नियम
- Cस्वतंत्र अपव्यूहन का नियम
- Dबहुगुणित नियम
Explanation
According to the Law of Independent Assortment, the inheritance of two different traits (such as seed colour and shape) is independent of each other.
Frequently Asked Questions
How many questions come from heredity in REET?+
REET 2024 had 2 questions from this topic, both based on disease-resistant crop varieties.
Why is Mendel called the 'father of genetics'?+
Mendel ran systematic experiments on pea plants and gave the three laws of heredity, which are still considered the foundation of genetics — this is why he is given this title. He chose pea plants for this work because they show clearly contrasting pairs of traits and can be grown through several generations quickly, and although he published his results in 1866, they were not recognised until after 1900, when three other scientists independently reached similar conclusions.
What is the difference between genotype and phenotype?+
Genotype is the genetic (gene) make-up of an organism, while phenotype is the organism's visible, outward traits.
What decides whether a baby will be a boy or a girl?+
This depends on whether an X or a Y sex chromosome is inherited from the father; the mother always contributes an X chromosome, so the father's contribution is decisive.
Which diseases are Pusa Swarnim and Himgiri resistant to?+
The mustard variety Pusa Swarnim was developed to resist white rust disease, and the wheat variety Himgiri was developed to resist leaf rust and hill bunt disease.
Why does variation matter in heredity?+
Because of variation, organisms of the same species are not all identical, which increases the species' chances of surviving a changing environment or a new disease — this is considered a basic requirement for evolution.
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Change Log
- 17 September 2026 — English page published — mirrors the fact-checked Hindi page, independently bilingual-accuracy checked