Class 12 : Biology (English) – Lesson 4 Principles of Inheritance and Variation
EXPLANATION & SUMMARY
✨ Introduction
🔵 Inheritance → Passing of traits 🧬 from parents 👩👩👦 to offspring.
🟢 Variation → Differences 🌱 among individuals of the same species.
🟠 Genetics → Science of heredity & variation.
🔴 Importance → Explains continuity of life 🔗, origin of new traits 🌟, and basis of evolution 🌍.
🌿 Mendel and His Experiments
👨🔬 Gregor Johann Mendel (1822–1884) → Father of Genetics.
📖 Work: Experiments on Plant Hybridisation (1865).
🌱 Experimental plant: Pea plant (Pisum sativum).
Why pea plant?
🌸 Clear contrasting traits (7 pairs).
⏱️ Short life cycle → quick results.
🌰 Produced large number of seeds.
🔀 Self-pollinating but cross-pollination possible.
Mendel’s Method
🧪 Maintained pure lines.
🎯 Studied one trait at a time.
📊 Counted large sample size.
🔢 Applied statistical analysis → accuracy.
🌱 Mendel’s Laws of Inheritance
⚡ Law of Dominance
In a hybrid (Aa), only the dominant allele shows its effect 💪, while the recessive remains hidden 👻.
Example: Tall (TT) × Dwarf (tt) → All Tall (Tt).
⚡ Law of Segregation (Purity of Gametes)
Allele pairs separate during gamete formation 🎲.
Each gamete gets only one allele.
Example: F2 of monohybrid cross = Phenotypic ratio 3 Tall : 1 Dwarf; Genotypic ratio 1:2:1.
⚡ Law of Independent Assortment
Alleles of different traits assort independently 🔄.
Example: Dihybrid cross (RRYY × rryy) → F2 ratio 9:3:3:1.
🧩 Mendel’s Crosses
🥬 Monohybrid Cross
P: TT × tt
F1: All Tt (Tall 🌱)
F2: 3 Tall : 1 Dwarf
🌽 Dihybrid Cross
P: RRYY × rryy
F1: All RrYy (Round Yellow 🌽)
F2: 9 Round Yellow : 3 Round Green : 3 Wrinkled Yellow : 1 Wrinkled Green
🎯 Why Mendel Succeeded
⭐ Choice of clear contrasting traits.
📘 Careful controlled pollination.
📊 Large data collection → statistical approach.
🌱 Use of true-breeding pea plants.
🌸 Deviations from Mendel’s Ratios
🎨 Incomplete Dominance → Hybrid shows blended trait (e.g., Red × White Snapdragon 🌸 = Pink).
🩸 Codominance → Both alleles expressed equally (e.g., Human ABO blood group IA + IB = AB).
🔀 Multiple Alleles → More than two alleles for a gene (e.g., ABO system IA, IB, i).
🧬 Pleiotropy → One gene influences multiple traits (e.g., Sickle-cell anaemia).
👥 Polygenic Inheritance → Multiple genes control one trait (e.g., Skin colour 👩🏽👩🏻👩🏿).
🧬 Chromosomal Basis of Inheritance
📌 Proposed by Sutton & Boveri (1902).
⚛️ Genes are located on chromosomes.
🔄 Behaviour of chromosomes during meiosis mirrors Mendel’s laws.
🔗 Linkage and Recombination
🔗 Linkage → Genes close together on same chromosome are inherited together.
🔄 Recombination → New allele combinations due to crossing over.
🪰 Studied by T.H. Morgan in fruit fly (Drosophila).
🚹 Mechanisms of Sex Determination
👨 XY system → Humans, Drosophila.
🐦 ZW system → Birds (ZW = female, ZZ = male).
🐝 Haplodiploidy → Honeybees (male = haploid, female = diploid).
⚡ Mutation
⚡ Sudden change in DNA sequence.
Types:
🎯 Point mutation → Single base change (e.g., sickle-cell).
🧩 Chromosomal mutation → Deletion, duplication, inversion, translocation.
🧪 Genetic Disorders
Mendelian Disorders
🩸 Haemophilia (X-linked recessive).
🧠 Phenylketonuria (autosomal recessive).
🩺 Sickle-cell anaemia (autosomal recessive).
Chromosomal Disorders
👶 Down’s syndrome (Trisomy 21).
👩 Turner’s syndrome (XO).
👨 Klinefelter’s syndrome (XXY).
📊 Hardy–Weinberg Principle
🧩 Statement: In a stable population with random mating, large size, and no mutation, migration, selection, or drift, allele frequencies remain constant.
Formula:
p + q = 1
p² + 2pq + q² = 1
Where:
p² → Homozygous dominant (AA)
2pq → Heterozygous (Aa)
q² → Homozygous recessive (aa)
⚠️ Deviations → Indicate evolutionary forces at work.
🧩 Pedigree Analysis
📜 Diagram tracing inheritance of traits.
Symbols: ⬜ Male, ⚪ Female, ⬛ Affected.
Useful in genetic counseling & studying disorders.
📝 Concise Summary (~300 words)
This chapter explains the principles of inheritance and variation. Mendel’s pea plant experiments gave us the laws of dominance, segregation, and independent assortment, explained through monohybrid (3:1) and dihybrid (9:3:3:1) ratios.
Later research found deviations: incomplete dominance, codominance, multiple alleles, pleiotropy, and polygenic inheritance. Sutton and Boveri’s chromosomal theory linked inheritance to chromosomes, while Morgan’s work on Drosophila revealed linkage and recombination.
Sex determination varies in different organisms: XY in humans, ZW in birds, haplodiploidy in honeybees. Mutations introduce new variations, and disorders are classified as Mendelian (haemophilia, phenylketonuria, sickle-cell) or chromosomal (Down’s, Turner’s, Klinefelter’s).
Population genetics is explained by the Hardy–Weinberg principle, stating that allele frequencies remain constant unless acted upon by evolutionary forces. Pedigree analysis helps trace inheritance and identify genetic disorders.
Thus, this chapter connects Mendel’s experiments with molecular genetics and evolution.
🎯 Quick Recap
🟦 Mendel’s Laws → Dominance, Segregation, Independent Assortment.
🟩 Crosses → Monohybrid (3:1), Dihybrid (9:3:3:1).
🟨 Exceptions → Incomplete dominance, codominance, multiple alleles, pleiotropy, polygenic inheritance.
🟧 Chromosomal Theory → Sutton & Boveri; Morgan’s linkage & recombination.
🟪 Sex Determination → XY (humans), ZW (birds), haplodiploidy (bees).
🟫 Mutations → Point & chromosomal.
⬜ Disorders → Mendelian (sickle-cell, haemophilia), Chromosomal (Down’s, Turner’s, Klinefelter’s).
🔵 Hardy–Weinberg → p² + 2pq + q² = 1.
🔴 Pedigree → Family inheritance charts.
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QUESTIONS FROM TEXTBOOK
Exercises Q&A
❓ Q1. Mention the advantages of selecting pea plant for experiment by Mendel.
✅ Answer:
🌱 Short life cycle → results obtained quickly.
🌸 Bisexual flowers → self-pollination, but cross-pollination possible.
🎨 Presence of 7 pairs of contrasting traits (e.g., tall/dwarf, round/wrinkled).
🌰 Large number of seeds produced → statistical accuracy.
🧪 Easy to cultivate & control pollination.
❓ Q2. Differentiate between the following –
(a) Dominance and Recessive
🌟 Dominant allele → Expressed in heterozygote (e.g., Tall in Tt).
🌑 Recessive allele → Masked in heterozygote, expressed only when homozygous (tt).
(b) Homozygous and Heterozygous
🟢 Homozygous → Both alleles identical (TT or tt).
🔵 Heterozygous → Two different alleles (Tt).
(c) Monohybrid and Dihybrid
🥬 Monohybrid → Cross involving a single trait (e.g., Tall × Dwarf).
🌽 Dihybrid → Cross involving two traits (e.g., Seed shape × Seed colour).
❓ Q3. A diploid organism is heterozygous for 4 loci, how many types of gametes can be produced?
✅ Answer (Stepwise):
🧮 Formula = , where n = number of heterozygous loci.
Here, n = 4.
Calculation: .
✅ Total gametes possible = 16.
❓ Q4. Explain the Law of Dominance using a monohybrid cross.
✅ Answer:
Law: In heterozygote (Aa), only one character (dominant) expresses, recessive remains hidden.
Example: Tall (TT) × Dwarf (tt)
🌱 P generation → TT × tt.
🌱 F1 → All Tt (Tall).
🌱 F2 → TT : Tt : tt = 1 : 2 : 1 (Genotypic).
Phenotypic ratio → 3 Tall : 1 Dwarf.
🎯 Conclusion: Dominant allele (T) masks recessive allele (t).
❓ Q5. Define and design a test-cross.
✅ Answer:
Definition: Crossing an individual with unknown genotype with a homozygous recessive to determine genotype.
Example: Tall plant of unknown genotype (T_) × dwarf plant (tt).
If all tall → parent = TT.
If 1 Tall : 1 Dwarf → parent = Tt.
❓ Q6. Using a Punnett Square, work out the distribution of phenotypic features in the first filial generation after a cross between a homozygous female and a heterozygous male for a single locus.
✅ Answer:
Let the trait = Tallness (T = tall, t = dwarf).
Parent: Homozygous female (TT) × Heterozygous male (Tt).
Gametes:
Female: T
Male: T, t
Punnett Square:T (♂) t (♂)
T (♀) TT Tt
Result: 50% TT, 50% Tt.
✅ All offspring Tall (100%).
❓ Q7. When a cross is made between tall plant with yellow seeds (TTyy) and tall plant with green seeds (Ttyy), what proportions of phenotype in the offspring could be expected to be –
(a) Tall and green
(b) Dwarf and green
✅ Answer (Stepwise):
Parents: TTyy × Ttyy.
Gametes:
TTyy → Ty.
Ttyy → Ty, ty.
Cross:
Ty × Ty = TTyy (Tall, Yellow).
Ty × ty = Ttyy (Tall, Yellow).
Result:
All offspring Tall, Yellow.
(a) Tall and Green = 0.
(b) Dwarf and Green = 0.
❓ Q8. Two heterozygous parents are crossed. If the two loci are linked, what would be the distribution of phenotypic features in F₁ generation for a dihybrid cross?
✅ Answer:
Parents: RrYy × RrYy (linked genes).
If completely linked, gametes formed will be RY, ry only.
Cross: RY × ry → Only Parental combinations.
Result: Only 2 phenotypes instead of 4 → 50% Round Yellow, 50% Wrinkled Green.
❓ Q9. Briefly mention the contribution of T.H. Morgan in genetics.
✅ Answer:
🪰 Worked on Drosophila melanogaster (fruit fly).
🔗 Discovered linkage of genes.
🔄 Studied recombination and crossing over.
📊 Introduced concept of gene mapping.
🏆 Awarded Nobel Prize (1933) for genetics research.
❓ Q10. What is pedigree analysis? Suggest how such an analysis can be useful.
✅ Answer:
Pedigree analysis → Diagrammatic record of inheritance across generations.
Usefulness:
🩺 Helps detect genetic disorders.
👨👩👧 Shows inheritance pattern (dominant, recessive, X-linked).
🧬 Useful in genetic counseling.
📚 Helps predict risk in future generations.
❓ Q11. How is sex determined in human beings?
✅ Answer:
Humans have 46 chromosomes (44 autosomes + XX/XY).
👩 Female → XX.
👨 Male → XY.
Egg always contributes X.
Sperm may contribute X or Y.
Fertilisation results:
X + X → Female child.
X + Y → Male child.
✅ Thus, male gamete determines the sex of the child.
❓ Q12. A child has blood group O. If the father has blood group A and mother blood group B, work out the genotypes of the parents and the possible genotypes of the other offspring.
✅ Answer (Stepwise):
Child with O = genotype ii.
Father has group A = possible genotype IAi.
Mother has group B = possible genotype IBi.
Cross: IAi × IBi
Gametes: IA, i (father) × IB, i (mother).
Punnett Square:
IAIB → AB group
IAi → A group
IBi → B group
ii → O group
✅ Possible offspring groups = A, B, AB, O.
❓ Q13. Explain the following terms with example:
(a) Codominance
Both alleles expressed equally in heterozygote.
Example: AB blood group (IA and IB).
(b) Incomplete dominance
Heterozygote shows intermediate phenotype.
Example: Snapdragon flower → Red × White = Pink.
❓ Q14. What is point mutation? Give one example.
✅ Answer:
A mutation affecting a single base pair.
Example: Sickle-cell anaemia (substitution of adenine → thymine in β-globin gene).
❓ Q15. Who had proposed the chromosomal theory of inheritance?
✅ Answer:
Sutton and Boveri (1902) proposed the Chromosomal Theory of Inheritance.
❓ Q16. Mention any two autosomal genetic disorders with their symptoms.
✅ Answer:
Sickle-cell anaemia (autosomal recessive)
Abnormal haemoglobin → sickle-shaped RBCs.
Symptoms: Anaemia, fatigue, joint pain.
Phenylketonuria (autosomal recessive)
Mutation in gene for phenylalanine metabolism.
Symptoms: Mental retardation, seizures, light skin/hair.
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OTHER IMPORTANT QUESTIONS FOR EXAMS
(CBSE MODEL QUESTION PAPER)
ESPECIALLY MADE FROM THIS CHAPTER ONLY
Full Board Style Solved Paper (33 Questions, 70 Marks)
🌟 Section A (1 Mark × 16 = 16 Marks, MCQs with Options)
Q1. Which of the following is a contrasting character studied by Mendel in pea plant?
🟦 (A) Tall vs Dwarf
🟩 (B) White vs Black flowers
🟨 (C) Smooth vs Rough seeds
🟧 (D) Pink vs Red flowers
✅ Answer: (A) Tall vs Dwarf
Q2. The genotype of a pure tall pea plant is:
🟦 (A) TT
🟩 (B) Tt
🟨 (C) tt
🟧 (D) None of these
✅ Answer: (A) TT
Q3. Law of Segregation was proposed by:
🟦 (A) T.H. Morgan
🟩 (B) Darwin
🟨 (C) Mendel
🟧 (D) Lamarck
✅ Answer: (C) Mendel
Q4. Which one is a sex-linked disorder?
🟦 (A) Phenylketonuria
🟩 (B) Haemophilia
🟨 (C) Sickle-cell anaemia
🟧 (D) Down’s syndrome
✅ Answer: (B) Haemophilia
Q5. The phenotypic ratio of a monohybrid cross is:
🟦 (A) 9:3:3:1
🟩 (B) 1:2:1
🟨 (C) 3:1
🟧 (D) 2:1
✅ Answer: (C) 3:1
Q6. In incomplete dominance, F₂ phenotypic ratio is:
🟦 (A) 1:2:1
🟩 (B) 3:1
🟨 (C) 9:3:3:1
🟧 (D) 2:1:1
✅ Answer: (A) 1:2:1
Q7. Number of different gametes produced by AaBbCc is:
🟦 (A) 2
🟩 (B) 4
🟨 (C) 8
🟧 (D) 16
✅ Answer: (C) 8
Q8. Who proposed the chromosomal theory of inheritance?
🟦 (A) Mendel
🟩 (B) Sutton & Boveri
🟨 (C) Watson & Crick
🟧 (D) Morgan
✅ Answer: (B) Sutton & Boveri
Q9. If frequency of allele ‘a’ = 0.4, frequency of ‘A’ = ?
🟦 (A) 0.4
🟩 (B) 0.6
🟨 (C) 0.8
🟧 (D) 0.2
✅ Answer: (B) 0.6
Q10. A cross between IAi × IBi can produce a child with blood group:
🟦 (A) A only
🟩 (B) AB only
🟨 (C) A, B, AB, O
🟧 (D) O only
✅ Answer: (C) A, B, AB, O
Q11. Example of polygenic inheritance is:
🟦 (A) AB blood group
🟩 (B) Skin colour in humans
🟨 (C) Sickle-cell anaemia
🟧 (D) Haemophilia
✅ Answer: (B) Skin colour in humans
Q12. Which of the following is a trisomy?
🟦 (A) Turner’s syndrome
🟩 (B) Klinefelter’s syndrome
🟨 (C) Down’s syndrome
🟧 (D) None
✅ Answer: (C) Down’s syndrome
Q13. Sex of child is determined by:
🟦 (A) Ovum
🟩 (B) Male gamete (sperm)
🟨 (C) Both
🟧 (D) None
✅ Answer: (B) Male gamete (sperm)
Q14. Which one shows codominance?
🟦 (A) ABO blood group
🟩 (B) Snapdragon flower colour
🟨 (C) Skin colour in humans
🟧 (D) Eye colour in Drosophila
✅ Answer: (A) ABO blood group
Q15. Crossing over occurs in:
🟦 (A) Mitosis metaphase
🟩 (B) Meiosis I prophase
🟨 (C) Meiosis II telophase
🟧 (D) None
✅ Answer: (B) Meiosis I prophase
Q16. Which disorder is caused by substitution mutation in haemoglobin?
🟦 (A) Phenylketonuria
🟩 (B) Sickle-cell anaemia
🟨 (C) Haemophilia
🟧 (D) Down’s syndrome
✅ Answer: (B) Sickle-cell anaemia
✨ Section B (2 marks × 6 = 12 marks)
Q17. Differentiate between dominance and recessiveness with one example each.
Answer:
🌟 Dominance: Allele that expresses in heterozygote. Example: Tall (T) in pea.
🌑 Recessiveness: Allele masked in heterozygote, expressed only in homozygote. Example: Dwarf (t) in pea.
Q18. What is linkage? How does it affect recombination?
Answer:
🔗 Linkage: Tendency of genes on the same chromosome (close together) to be inherited together.
🔄 Effect: Decreases recombination → fewer new combinations, more parental types.
Q19. Show the outcome of a test cross Tt × tt using a Punnett square.
Answer:
🧬 Gametes: (T, t) from Tt; (t) from tt.
🧮 Cross:
T × t = Tt (Tall)
t × t = tt (Dwarf)
✅ Phenotype ratio: 1 Tall : 1 Dwarf.
Q20. Why does the father determine the sex of a human child?
Answer:
👩 Eggs always carry X.
👨 Sperms carry X or Y.
🧷 Fertilisation results:
X (egg) + X (sperm) = XX (female)
X (egg) + Y (sperm) = XY (male)
✅ Thus, sperm from father decides the sex.
Q21. Define mutation. Distinguish point vs chromosomal mutations.
Answer:
⚡ Mutation: Sudden heritable change in DNA sequence.
🎯 Point mutation: Single base change (e.g., sickle-cell anaemia).
🧩 Chromosomal mutation: Large-scale alteration (deletion, duplication, inversion, translocation).
Q22. What is pedigree analysis? Mention one importance.
Answer:
📜 Pedigree analysis: Diagram showing inheritance of a trait across generations.
🎯 Use: Helps identify mode of inheritance and detect genetic disorders.
🔬 Section C (3 marks × 6 = 18 marks)
Q23. Explain incomplete dominance in snapdragon with cross and ratio.
Answer:
🎨 Concept: Heterozygote shows intermediate phenotype.
🌸 Cross: Red (RR) × White (rr) → F₁: Rr (Pink).
🔁 F₂: Rr × Rr = 1 RR (Red) : 2 Rr (Pink) : 1 rr (White).
Q24. State the Law of Independent Assortment. Verify with a dihybrid cross.
Answer:
📘 Law: Alleles of different genes assort independently if not linked.
🌽 Cross: RRYY × rryy → F₁: RrYy (Round Yellow).
🔁 F₂: Produces phenotypic ratio 9:3:3:1.
Q25. Describe inheritance of haemophilia. Why is it more common in males?
Answer:
🩸 Type: X-linked recessive disorder.
👩 Female (XX): requires two defective Xs → rare.
👨 Male (XY): one defective X → disease expressed.
✅ Therefore, males are more commonly affected.
Q26. How many different gametes can an organism with genotype AaBbCc produce? Show steps.
Answer:
Rule: Number of gamete types = 2ⁿ, n = heterozygous loci.
1️⃣ n = 3 (A, B, C heterozygous).
2️⃣ 2³ = 8.
✅ Total gametes = 8.
Q27. Write any three reasons for Mendel’s success in his experiments.
Answer:
🌱 Chose contrasting traits.
🌸 Used pure lines & controlled pollination.
📊 Collected large data and applied statistics.
Q28. A child has O blood group. Father is A, mother is B. Work out possible parental genotypes and children’s blood groups.
Answer:
👶 Child O ⇒ genotype ii.
👨 Father A ⇒ must be Iᴬi.
👩 Mother B ⇒ must be Iᴮi.
🧮 Cross: Iᴬi × Iᴮi → offspring = A, B, AB, O.
✅ All four blood groups possible.
📚 Section D (Case-based, 4 marks × 2 = 8 marks)
Q29. Hardy–Weinberg Case: In a population, 36% individuals are recessive aa. Calculate q, p, heterozygotes, and list disturbing forces.
Answer:
1️⃣ q² = 0.36 → q = 0.6.
2️⃣ p = 1 − q = 0.4.
3️⃣ Heterozygotes = 2pq = 0.48 = 48%.
4️⃣ Disturbing forces: mutation, migration, natural selection, genetic drift, non-random mating, small population size.
Q30. Pedigree Case (Haemophilia):
Answer:
(a) Type = X-linked recessive.
(b) More common in males → they are hemizygous (XY).
(c) Carrier mother (XᴴXʰ) × normal father (XᴴY) → 50% sons haemophilic.
(d) Importance → predicts risk, useful in genetic counselling.
🧬 Section E (Long answer, 5 marks × 3 = 15 marks)
Q31. Explain Morgan’s linkage–recombination experiments in Drosophila.
Answer:
🪰 Used fruit fly → short life, many progeny.
🔗 Found some traits inherited together = linkage.
🔄 Crossing over produced recombinants.
📏 Calculated recombination % → mapped genes.
✅ Conclusion: Closer genes = stronger linkage, less recombination.
Q32. Describe Mendel’s monohybrid cross and compare ratios.
Answer:
🌱 P: TT × tt → F₁: Tt (all tall).
🌱 F₂: Tt × Tt = 1 TT : 2 Tt : 1 tt.
Genotypic ratio: 1:2:1.
Phenotypic ratio: 3 Tall : 1 Dwarf.
✅ Shows dominance + segregation.
Q33. Describe any two autosomal genetic disorders with causes and symptoms.
Answer:
Sickle-cell anaemia (autosomal recessive)
Cause: Point mutation in β-globin gene.
Effect: HbS polymerises → sickle-shaped RBCs.
Symptoms: Anaemia, pain, fatigue.
Phenylketonuria (autosomal recessive)
Cause: Defective enzyme for phenylalanine metabolism.
Effect: Toxic phenylalanine buildup.
Symptoms: Intellectual disability, seizures, fair skin.
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NEET QUESTIONS FROM THIS LESSON
🔹 Q1. Which of the following pairs is wrongly matched?
🔵 (A) Starch synthesis in pea : Multiple alleles
🟢 (B) ABO blood grouping : Co-dominance
🟠 (C) XO type sex determination : Grasshopper
🔴 (D) T.H. Morgan : Linkage
✔️ Answer: (A) Starch synthesis in pea : Multiple alleles
Exam: NEET 2018
🔹 Q2. Which of the following characteristics represent inheritance of blood groups in humans?
(i) Dominance (ii) Co-dominance (iii) Multiple alleles (iv) Incomplete dominance (v) Polygenic inheritance
🔵 (A) (ii), (iii) and (v)
🟢 (B) (i), (ii) and (iii)
🟠 (C) (ii), (iv) and (v)
🔴 (D) (i), (iii) and (v)
✔️ Answer: (B) (i), (ii) and (iii)
Exam: NEET 2018
🔹 Q3. A woman has an X-linked condition on one of her X chromosomes. This chromosome can be inherited by:
🔵 (A) Only daughters
🟢 (B) Only sons
🟠 (C) Only grandchildren
🔴 (D) Both sons and daughters
✔️ Answer: (D) Both sons and daughters
Exam: NEET 2018
🔹 Q4. Which one from those given below is the period for Mendel’s hybridisation experiments?
🔵 (A) 1840–1850
🟢 (B) 1857–1869
🟠 (C) 1870–1877
🔴 (D) 1856–1863
✔️ Answer: (D) 1856–1863
Exam: NEET 2017
🔹 Q5. A disease caused by an autosomal primary nondisjunction is:
🔵 (A) Klinefelter’s syndrome
🟢 (B) Down’s syndrome
🟠 (C) Turner’s syndrome
🔴 (D) Sickle-cell anaemia
✔️ Answer: (B) Down’s syndrome
Exam: NEET 2017
🔹 Q6. Among the following characters, which one was not considered by Mendel in his experiments on pea?
🔵 (A) Trichomes—Glandular or non-glandular
🟢 (B) Seed—Green or yellow
🟠 (C) Pod—Inflated or constricted
🔴 (D) Stem—Tall or dwarf
✔️ Answer: (A) Trichomes—Glandular or non-glandular
Exam: NEET 2017
🔹 Q7. Parents: IAIB and IAi. How many phenotypes are possible among the children?
🔵 (A) 4
🟢 (B) 3
🟠 (C) 2
🔴 (D) 1
✔️ Answer: (B) 3
Exam: NEET 2017
🔹 Q8. In Snapdragon, red × white gives pink in F1. On selfing pink, F2 shows red, pink and white. Choose the incorrect statement.
🔵 (A) Law of Segregation does not apply here
🟢 (B) Principle of Dominance does not hold true here
🟠 (C) Pink in F1 is due to incomplete dominance
🔴 (D) F2 ratio is 1/4 red : 1/2 pink : 1/4 white
✔️ Answer: (A) Law of Segregation does not apply here
Exam: NEET 2019
🔹 Q9. A gene locus has two alleles A and a. If frequency of A = 0.4, the frequencies of AA, Aa, aa under Hardy–Weinberg equilibrium are:
🔵 (A) 0.16, 0.48, 0.36
🟢 (B) 0.16, 0.36, 0.48
🟠 (C) 0.36, 0.48, 0.16
🔴 (D) 0.16, 0.24, 0.36
✔️ Answer: (A) 0.16, 0.48, 0.36
Exam: NEET 2019
🔹 Q10. In Snapdragon, red × white gives pink in F1. This is an example of:
🔵 (A) Codominance
🟢 (B) Incomplete dominance
🟠 (C) Overdominance
🔴 (D) Epistasis
✔️ Answer: (B) Incomplete dominance
Exam: NEET 2022
🔹 Q11. Experimental verification of the chromosomal theory of inheritance was done by:
🔵 (A) Mendel
🟢 (B) Sutton
🟠 (C) Boveri
🔴 (D) T.H. Morgan
✔️ Answer: (D) T.H. Morgan
Exam: NEET 2020
🔹 Q12. Which of the following pairs is correctly matched for sex-determination system?
🔵 (A) Humans – ZW–ZZ
🟢 (B) Birds – ZW–ZZ
🟠 (C) Grasshopper – ZZ–ZW
🔴 (D) Drosophila – XO–XX
✔️ Answer: (B) Birds – ZW–ZZ
Exam: NEET 2019
🔹 Q13. Which genetic disorder shows XXY karyotype with masculine development and gynaecomastia?
🔵 (A) Turner’s syndrome
🟢 (B) Klinefelter’s syndrome
🟠 (C) Down’s syndrome
🔴 (D) Edwards syndrome
✔️ Answer: (B) Klinefelter’s syndrome
Exam: NEET 2019
🔹 Q14. The frequency of recombination between gene pairs on the same chromosome as a measure of distance between genes was first explained by:
🔵 (A) Alfred Sturtevant
🟢 (B) Sutton & Boveri
🟠 (C) Gregor Mendel
🔴 (D) T.H. Morgan
✔️ Answer: (A) Alfred Sturtevant
Exam: NEET 2019
🔹 Q15. XO type of sex determination is typically found in:
🔵 (A) Birds
🟢 (B) Humans
🟠 (C) Grasshopper
🔴 (D) Drosophila
✔️ Answer: (C) Grasshopper
Exam: AIPMT 2015
🔹 Q16. Which law of inheritance is universally applicable without exception?
🔵 (A) Law of dominance
🟢 (B) Law of segregation
🟠 (C) Law of independent assortment
🔴 (D) Law of unit characters
✔️ Answer: (B) Law of segregation
Exam: NEET 2016
🔹 Q17. A child with blood group O cannot have parents with blood groups:
🔵 (A) A and B
🟢 (B) B and O
🟠 (C) A and AB
🔴 (D) O and O
✔️ Answer: (C) A and AB
Exam: AIPMT 2014
🔹 Q18. Which disorder is due to recessive autosomal mutation?
🔵 (A) Down’s syndrome
🟢 (B) Sickle-cell anaemia
🟠 (C) Klinefelter’s syndrome
🔴 (D) Turner’s syndrome
✔️ Answer: (B) Sickle-cell anaemia
Exam: NEET 2018
🔹 Q19. The condition where an individual has both alleles fully expressed is called:
🔵 (A) Dominance
🟢 (B) Codominance
🟠 (C) Incomplete dominance
🔴 (D) Pleiotropy
✔️ Answer: (B) Codominance
Exam: NEET 2016
🔹 Q20. If in a population the frequency of allele A is 0.3, the frequency of Aa genotype under Hardy–Weinberg equilibrium is:
🔵 (A) 0.09
🟢 (B) 0.21
🟠 (C) 0.42
🔴 (D) 0.49
✔️ Answer: (C) 0.42
Exam: NEET 2017
🔹 Q21. Which one of the following is not a Mendelian disorder?
🔵 (A) Sickle-cell anaemia
🟢 (B) Thalassemia
🟠 (C) Haemophilia
🔴 (D) Down’s syndrome
✔️ Answer: (D) Down’s syndrome
Exam: NEET 2016
🔹 Q22. A man with colour-blind mother and a normal father marries a woman with normal parents. Their sons will be:
🔵 (A) All colour-blind
🟢 (B) All normal
🟠 (C) 50% colour-blind
🔴 (D) 25% colour-blind
✔️ Answer: (B) All normal
Exam: NEET 2015
🔹 Q23. Which scientist worked on Drosophila to provide proof for the chromosomal theory of inheritance?
🔵 (A) Hugo de Vries
🟢 (B) T.H. Morgan
🟠 (C) Gregor Mendel
🔴 (D) Alfred Sturtevant
✔️ Answer: (B) T.H. Morgan
Exam: NEET 2020
🔹 Q24. Genetic drift operates in:
🔵 (A) Large populations
🟢 (B) Small populations
🟠 (C) Populations with gene flow
🔴 (D) Only laboratory populations
✔️ Answer: (B) Small populations
Exam: AIPMT 2011
🔹 Q25. Which of the following diseases is NOT sex-linked?
🔵 (A) Haemophilia
🟢 (B) Colour blindness
🟠 (C) Duchenne muscular dystrophy
🔴 (D) Sickle-cell anaemia
✔️ Answer: (D) Sickle-cell anaemia
🔹 Q26. The human male inherits his X chromosome from:
🔵 (A) Father
🟢 (B) Mother
🟠 (C) Both parents
🔴 (D) Either parent
✔️ Answer: (B) Mother
Exam: NEET 2018
🔹 Q27. Which type of sex determination is shown by grasshopper?
🔵 (A) XY type
🟢 (B) XO type
🟠 (C) ZW type
🔴 (D) Haplodiploidy
✔️ Answer: (B) XO type
Exam: AIPMT 2012
🔹 Q28. When two alleles of a gene pair express themselves equally in heterozygote, it is known as:
🔵 (A) Incomplete dominance
🟢 (B) Codominance
🟠 (C) Overdominance
🔴 (D) Pleiotropy
✔️ Answer: (B) Codominance
Exam: AIPMT 2010
🔹 Q29. Which disorder occurs due to monosomy of sex chromosome?
🔵 (A) Turner’s syndrome
🟢 (B) Down’s syndrome
🟠 (C) Klinefelter’s syndrome
🔴 (D) Cri-du-chat syndrome
✔️ Answer: (A) Turner’s syndrome
Exam: NEET 2019
🔹 Q30. The phenomenon of crossing-over occurs during:
🔵 (A) Leptotene
🟢 (B) Pachytene
🟠 (C) Diplotene
🔴 (D) Zygotene
✔️ Answer: (B) Pachytene
Exam: NEET 2016
🔹 Q31. The number of contrasting traits studied by Mendel in pea was:
🔵 (A) 5
🟢 (B) 6
🟠 (C) 7
🔴 (D) 8
✔️ Answer: (C) 7
Exam: NEET 2019
🔹 Q32. Which of the following is an example of pleiotropy?
🔵 (A) ABO blood group
🟢 (B) Sickle-cell anaemia
🟠 (C) Haemophilia
🔴 (D) Down’s syndrome
✔️ Answer: (B) Sickle-cell anaemia
Exam: NEET 2018
🔹 Q33. The proportion of heterozygotes under Hardy–Weinberg equilibrium is represented by:
🔵 (A) p^2
🟢 (B) q^2
🟠 (C) 2pq
🔴 (D) (p+q)^2
✔️ Answer: (C) 2pq
Exam: NEET 2017
🔹 Q34. Who coined the term “linkage”?
🔵 (A) Bateson
🟢 (B) Mendel
🟠 (C) T.H. Morgan
🔴 (D) Darwin
✔️ Answer: (A) Bateson
Exam: AIPMT 2008
🔹 Q35. Which scientist constructed the first genetic map of Drosophila using recombination frequency?
🔵 (A) Alfred Sturtevant
🟢 (B) Mendel
🟠 (C) Sutton
🔴 (D) Boveri
✔️ Answer: (A) Alfred Sturtevant
Exam: NEET 2019
🔹 Q36. Which syndrome shows trisomy of chromosome 21?
🔵 (A) Turner’s syndrome
🟢 (B) Down’s syndrome
🟠 (C) Klinefelter’s syndrome
🔴 (D) Patau’s syndrome
✔️ Answer: (B) Down’s syndrome
Exam: NEET 2017
🔹 Q37. The phenotypic ratio of a monohybrid cross in F2 generation is:
🔵 (A) 1:1
🟢 (B) 1:2:1
🟠 (C) 3:1
🔴 (D) 9:3:3:1
✔️ Answer: (C) 3:1
Exam: NEET 2016
🔹 Q38. A pleiotropic gene influences:
🔵 (A) Single trait
🟢 (B) Multiple traits
🟠 (C) Only recessive traits
🔴 (D) Only sex-linked traits
✔️ Answer: (B) Multiple traits
Exam: NEET 2015
🔹 Q39. Which of the following is a sex-linked disorder?
🔵 (A) Sickle-cell anaemia
🟢 (B) Colour blindness
🟠 (C) Thalassemia
🔴 (D) Down’s syndrome
✔️ Answer: (B) Colour blindness
Exam: NEET 2017
🔹 Q40. Which law of inheritance is also called “law of purity of gametes”?
🔵 (A) Law of dominance
🟢 (B) Law of segregation
🟠 (C) Law of independent assortment
🔴 (D) Law of probability
✔️ Answer: (B) Law of segregation
Exam: AIPMT 2009
🔹 Q41. In humans, sex of child is determined by:
🔵 (A) Chromosome type in sperm
🟢 (B) Chromosome type in egg
🟠 (C) Number of autosomes
🔴 (D) Cytoplasm of zygote
✔️ Answer: (A) Chromosome type in sperm
Exam: NEET 2019
🔹 Q42. In a dihybrid cross, the phenotypic ratio in F2 generation is:
🔵 (A) 9:3:3:1
🟢 (B) 3:1
🟠 (C) 1:2:1
🔴 (D) 1:1:1:1
✔️ Answer: (A) 9:3:3:1
Exam: NEET 2016
🔹 Q43. The inheritance pattern of haemophilia is:
🔵 (A) Autosomal dominant
🟢 (B) Autosomal recessive
🟠 (C) X-linked recessive
🔴 (D) Y-linked
✔️ Answer: (C) X-linked recessive
Exam: NEET 2015
🔹 Q44. Which of the following is an autosomal dominant disorder?
🔵 (A) Myotonic dystrophy
🟢 (B) Cystic fibrosis
🟠 (C) Haemophilia
🔴 (D) Colour blindness
✔️ Answer: (A) Myotonic dystrophy
Exam: NEET 2022
🔹 Q45. Independent assortment is possible when:
🔵 (A) Genes are on different chromosomes
🟢 (B) Genes are tightly linked
🟠 (C) Genes are on the same locus
🔴 (D) Genes are pleiotropic
✔️ Answer: (A) Genes are on different chromosomes
Exam: NEET 2016
🔹 Q46. The probability of a colour-blind son if mother is carrier and father is normal is:
🔵 (A) 25%
🟢 (B) 50%
🟠 (C) 75%
🔴 (D) 100%
✔️ Answer: (B) 50%
Exam: NEET 2017
🔹 Q47. Which law did Mendel derive from monohybrid cross?
🔵 (A) Law of dominance
🟢 (B) Law of segregation
🟠 (C) Law of independent assortment
🔴 (D) Both (A) and (B)
✔️ Answer: (D) Both (A) and (B)
Exam: AIPMT 2010
🔹 Q48. Which syndrome has genotype 44+XO?
🔵 (A) Turner’s syndrome
🟢 (B) Down’s syndrome
🟠 (C) Klinefelter’s syndrome
🔴 (D) Edward’s syndrome
✔️ Answer: (A) Turner’s syndrome
Exam: NEET 2019
🔹 Q49. The phenomenon of linkage was first observed in:
🔵 (A) Drosophila
🟢 (B) Pea
🟠 (C) Grasshopper
🔴 (D) Maize
✔️ Answer: (A) Drosophila
Exam: NEET 2020
🔹 Q50. The total number of linkage groups in human genome equals the number of:
🔵 (A) Autosomes
🟢 (B) Chromosomes
🟠 (C) Homologous pairs of chromosomes
🔴 (D) Chromatids at metaphase
✔️ Answer: (B) Chromosomes (23)
Exam: NEET 2016
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PRACTICE SETS FROM THIS LESSON
🔹 Q1. Mendel selected pea plant for his experiments because:
🔵 (A) Cross-pollination is natural in pea
🟢 (B) It has long life cycle and few traits
🟠 (C) It has contrasting traits and short life cycle
🔴 (D) It cannot be self-pollinated
✔️ Answer: (C) It has contrasting traits and short life cycle
🔹 Q2. Which of the following shows incomplete dominance?
🔵 (A) ABO blood group in humans
🟢 (B) Flower colour in Snapdragon
🟠 (C) Haemophilia
🔴 (D) Colour blindness
✔️ Answer: (B) Flower colour in Snapdragon
🔹 Q3. If a heterozygous tall pea plant is self-crossed, the expected ratio of tall to dwarf plants in F2 is:
🔵 (A) 1:1
🟢 (B) 3:1
🟠 (C) 9:3:3:1
🔴 (D) 2:1
✔️ Answer: (B) 3:1
🔹 Q4. Which law of Mendel is called “Law of purity of gametes”?
🔵 (A) Law of dominance
🟢 (B) Law of segregation
🟠 (C) Law of independent assortment
🔴 (D) Law of unit characters
✔️ Answer: (B) Law of segregation
🔹 Q5. In dihybrid cross, the appearance of new combinations in F2 proves:
🔵 (A) Codominance
🟢 (B) Independent assortment
🟠 (C) Pleiotropy
🔴 (D) Linkage
✔️ Answer: (B) Independent assortment
🔹 Q6. Which of the following is an example of pleiotropy?
🔵 (A) Sickle-cell anaemia
🟢 (B) ABO blood group
🟠 (C) Colour blindness
🔴 (D) Down’s syndrome
✔️ Answer: (A) Sickle-cell anaemia
🔹 Q7. A cross between IAIB × ii will produce children with blood groups:
🔵 (A) A and B only
🟢 (B) A, B and O
🟠 (C) AB and O
🔴 (D) All four types
✔️ Answer: (A) A and B only
🔹 Q8. Which condition in humans is due to monosomy of sex chromosome?
🔵 (A) Turner’s syndrome
🟢 (B) Down’s syndrome
🟠 (C) Klinefelter’s syndrome
🔴 (D) Edward’s syndrome
✔️ Answer: (A) Turner’s syndrome
🔹 Q9. A heterozygous plant shows phenotype of dominant trait because:
🔵 (A) Dominant allele expresses itself in presence of recessive
🟢 (B) Recessive allele suppresses dominant one
🟠 (C) Both alleles are equally expressed
🔴 (D) Neither allele is expressed
✔️ Answer: (A) Dominant allele expresses itself in presence of recessive
🔹 Q10. Which disorder is caused by absence of clotting factor VIII?
🔵 (A) Thalassemia
🟢 (B) Sickle-cell anaemia
🟠 (C) Haemophilia
🔴 (D) Colour blindness
✔️ Answer: (C) Haemophilia
🔹 Q11. Which ratio indicates incomplete dominance in F2 generation?
🔵 (A) 3:1
🟢 (B) 9:3:3:1
🟠 (C) 1:2:1
🔴 (D) 1:1:1:1
✔️ Answer: (C) 1:2:1
🔹 Q12. Which scientist provided experimental evidence for chromosomal theory of inheritance?
🔵 (A) Alfred Sturtevant
🟢 (B) Sutton
🟠 (C) T.H. Morgan
🔴 (D) Darwin
✔️ Answer: (C) T.H. Morgan
🔹 Q13. The probability of a colour-blind son if mother is a carrier and father is normal is:
🔵 (A) 0%
🟢 (B) 25%
🟠 (C) 50%
🔴 (D) 100%
✔️ Answer: (C) 50%
🔹 Q14. Which of the following is NOT a Mendelian disorder?
🔵 (A) Sickle-cell anaemia
🟢 (B) Haemophilia
🟠 (C) Down’s syndrome
🔴 (D) Thalassemia
✔️ Answer: (C) Down’s syndrome
🔹 Q15. The total number of linkage groups in humans is:
🔵 (A) 22
🟢 (B) 23
🟠 (C) 44
🔴 (D) 46
✔️ Answer: (B) 23
🔹 Q16. Who coined the term “linkage”?
🔵 (A) Bateson
🟢 (B) Mendel
🟠 (C) Darwin
🔴 (D) Hugo de Vries
✔️ Answer: (A) Bateson
🔹 Q17. A gene influencing more than one trait is known as:
🔵 (A) Epistatic gene
🟢 (B) Pleiotropic gene
🟠 (C) Polygenic gene
🔴 (D) Regulatory gene
✔️ Answer: (B) Pleiotropic gene
🔹 Q18. Which is an example of codominance in humans?
🔵 (A) Skin colour
🟢 (B) ABO blood group
🟠 (C) Height
🔴 (D) Haemophilia
✔️ Answer: (B) ABO blood group
🔹 Q19. In which phase of meiosis does crossing-over occur?
🔵 (A) Zygotene
🟢 (B) Pachytene
🟠 (C) Diplotene
🔴 (D) Diakinesis
✔️ Answer: (B) Pachytene
🔹 Q20. A carrier woman for haemophilia and a normal man have a son. Probability that the son will be haemophilic is:
🔵 (A) 0%
🟢 (B) 25%
🟠 (C) 50%
🔴 (D) 100%
✔️ Answer: (C) 50%
🔹 Q21. Independent assortment of genes occurs when:
🔵 (A) Genes are tightly linked
🟢 (B) Genes are on different chromosomes
🟠 (C) Genes are allelic
🔴 (D) Genes are pleiotropic
✔️ Answer: (B) Genes are on different chromosomes
🔹 Q22. Which genetic disorder is caused by substitution of a single base in β-globin gene?
🔵 (A) Haemophilia
🟢 (B) Sickle-cell anaemia
🟠 (C) Down’s syndrome
🔴 (D) Klinefelter’s syndrome
✔️ Answer: (B) Sickle-cell anaemia
🔹 Q23. If frequency of allele A = 0.7 and a = 0.3, then frequency of heterozygotes (Aa) under Hardy–Weinberg equilibrium is:
🔵 (A) 0.42
🟢 (B) 0.49
🟠 (C) 0.21
🔴 (D) 0.09
✔️ Answer: (A) 0.42
🔹 Q24. Which disorder shows trisomy of chromosome 21?
🔵 (A) Turner’s syndrome
🟢 (B) Down’s syndrome
🟠 (C) Klinefelter’s syndrome
🔴 (D) Cri-du-chat syndrome
✔️ Answer: (B) Down’s syndrome
🔹 Q25. Which of the following is an example of polygenic inheritance?
🔵 (A) ABO blood group
🟢 (B) Colour blindness
🟠 (C) Skin colour in humans
🔴 (D) Haemophilia
✔️ Answer: (C) Skin colour in humans
🔹 Q26. Which of the following is an example of epistasis?
🔵 (A) Flower colour in Snapdragon
🟢 (B) Coat colour in mice
🟠 (C) ABO blood group
🔴 (D) Sickle-cell anaemia
✔️ Answer: (B) Coat colour in mice
🔹 Q27. Which of the following is a sex-linked recessive disorder?
🔵 (A) Sickle-cell anaemia
🟢 (B) Haemophilia
🟠 (C) Thalassemia
🔴 (D) Down’s syndrome
✔️ Answer: (B) Haemophilia
🔹 Q28. Who formulated the “Chromosomal Theory of Inheritance”?
🔵 (A) Mendel
🟢 (B) Sutton and Boveri
🟠 (C) Darwin
🔴 (D) Hugo de Vries
✔️ Answer: (B) Sutton and Boveri
🔹 Q29. Which is true for codominance but not for incomplete dominance?
🔵 (A) Both alleles are expressed simultaneously
🟢 (B) One allele masks the other
🟠 (C) Intermediate phenotype is produced
🔴 (D) Segregation does not occur
✔️ Answer: (A) Both alleles are expressed simultaneously
🔹 Q30. The probability of a child being a carrier of sickle-cell trait if both parents are heterozygous is:
🔵 (A) 25%
🟢 (B) 50%
🟠 (C) 75%
🔴 (D) 100%
✔️ Answer: (B) 50%
🔹 Q31. Which of the following is not a sex-linked trait?
🔵 (A) Colour blindness
🟢 (B) Haemophilia
🟠 (C) Sickle-cell anaemia
🔴 (D) Duchenne muscular dystrophy
✔️ Answer: (C) Sickle-cell anaemia
🔹 Q32. The probability of producing a haemophilic daughter from a haemophilic father and carrier mother is:
🔵 (A) 0%
🟢 (B) 25%
🟠 (C) 50%
🔴 (D) 100%
✔️ Answer: (B) 25%
🔹 Q33. Which of the following best explains polygenic inheritance?
🔵 (A) ABO blood group
🟢 (B) Human height
🟠 (C) Haemophilia
🔴 (D) Colour blindness
✔️ Answer: (B) Human height
🔹 Q34. If both parents are heterozygous for blood group A (IAi), the possible blood groups of their children are:
🔵 (A) A and O
🟢 (B) A, B, O
🟠 (C) A, AB, O
🔴 (D) A, B, AB, O
✔️ Answer: (A) A and O
🔹 Q35. In pedigree analysis, a trait that appears in every generation is most likely:
🔵 (A) Autosomal recessive
🟢 (B) Autosomal dominant
🟠 (C) X-linked recessive
🔴 (D) Y-linked
✔️ Answer: (B) Autosomal dominant
🔹 Q36. Which of the following indicates pleiotropy?
🔵 (A) Single gene affecting multiple traits
🟢 (B) Multiple genes affecting single trait
🟠 (C) Both alleles expressed equally
🔴 (D) One gene suppresses another
✔️ Answer: (A) Single gene affecting multiple traits
🔹 Q37. What is the probability of obtaining a dwarf pea plant from Tt × Tt?
🔵 (A) 0.25
🟢 (B) 0.50
🟠 (C) 0.75
🔴 (D) 1
✔️ Answer: (A) 0.25
🔹 Q38. In Hardy–Weinberg equilibrium, 2pq represents:
🔵 (A) Frequency of homozygous dominant
🟢 (B) Frequency of heterozygotes
🟠 (C) Frequency of homozygous recessive
🔴 (D) Total allele frequency
✔️ Answer: (B) Frequency of heterozygotes
🔹 Q39. Which of the following is NOT a feature of Mendel’s experiments?
🔵 (A) Large sample size
🟢 (B) Statistical analysis
🟠 (C) Study of trichome characters
🔴 (D) Use of contrasting traits
✔️ Answer: (C) Study of trichome characters
🔹 Q40. A cross between red × white flowered Snapdragon gives pink. The inheritance pattern is:
🔵 (A) Codominance
🟢 (B) Incomplete dominance
🟠 (C) Polygenic inheritance
🔴 (D) Epistasis
✔️ Answer: (B) Incomplete dominance
🔹 Q41. A woman with genotype XCXc (carrier for colour blindness) marries a normal man. Probability of colour-blind son is:
🔵 (A) 0%
🟢 (B) 25%
🟠 (C) 50%
🔴 (D) 100%
✔️ Answer: (B) 25%
🔹 Q42. Which one of the following statements is correct about Down’s syndrome?
🔵 (A) It is a monosomy of chromosome 21
🟢 (B) It is a trisomy of chromosome 21
🟠 (C) It is due to deletion of chromosome 21
🔴 (D) It is due to duplication of chromosome 21
✔️ Answer: (B) It is a trisomy of chromosome 21
🔹 Q43. The F2 ratio of a dihybrid cross in pea plants is:
🔵 (A) 9:3:3:1
🟢 (B) 3:1
🟠 (C) 1:2:1
🔴 (D) 1:1
✔️ Answer: (A) 9:3:3:1
🔹 Q44. Which of the following best explains codominance?
🔵 (A) IA and IB alleles in ABO blood group
🟢 (B) Skin colour in humans
🟠 (C) Flower colour in Snapdragon
🔴 (D) Sickle-cell anaemia
✔️ Answer: (A) IA and IB alleles in ABO blood group
🔹 Q45. Which scientist gave the first experimental proof of linkage?
🔵 (A) Mendel
🟢 (B) T.H. Morgan
🟠 (C) Sutton
🔴 (D) Darwin
✔️ Answer: (B) T.H. Morgan
🔹 Q46. Which law can be explained by segregation of alleles during gamete formation?
🔵 (A) Law of dominance
🟢 (B) Law of segregation
🟠 (C) Law of independent assortment
🔴 (D) Law of linkage
✔️ Answer: (B) Law of segregation
🔹 Q47. A male child is born colour blind if:
🔵 (A) Mother is carrier, father is colour blind
🟢 (B) Mother is normal, father is colour blind
🟠 (C) Mother is carrier, father is normal
🔴 (D) Both parents normal
✔️ Answer: (C) Mother is carrier, father is normal
🔹 Q48. Which of the following conditions is characterised by genotype 47, XXY?
🔵 (A) Turner’s syndrome
🟢 (B) Down’s syndrome
🟠 (C) Klinefelter’s syndrome
🔴 (D) Edwards syndrome
✔️ Answer: (C) Klinefelter’s syndrome
🔹 Q49. Which of the following is NOT a feature of polygenic inheritance?
🔵 (A) Continuous variation
🟢 (B) Influence of environment
🟠 (C) Involvement of multiple genes
🔴 (D) Clear-cut Mendelian ratios
✔️ Answer: (D) Clear-cut Mendelian ratios
🔹 Q50. Which of the following is NOT a Mendelian disorder?
🔵 (A) Thalassemia
🟢 (B) Sickle-cell anaemia
🟠 (C) Haemophilia
🔴 (D) Down’s syndrome
✔️ Answer: (D) Down’s syndrome
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MIND MAPS
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