CUET UG Categorised PYQ Biology Unit 4 -

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CUET UG Categorised PYQ Biology Unit 4

BIOLOGY

⏱️ 30 Minutes

❓ 20 Questions

📅 2022, 2023, 2024 & 2025

✍️ Long Answers

📌 Answers are locked once submitted — results and explanations appear at the end.

CUET UG Categorised PYQ Biology Unit 4

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QUESTION 1 OF 20

📄 Passage

Which of the following genetic disorder is not a type of Mendelian disorder? (PYQ 2023 Shift 1)

Answer Review

📄 Passage

Which of the following genetic disorder is not a type of Mendelian disorder? (PYQ 2023 Shift 1)

A Colour blindness

B Down's syndrome

C Haemophilia

D Thalassemia

💡 Short Explanation

Down syndrome is chromosomal. Mendelian disorders involve single genes. Aneuploidy causes Down syndrome.

✅ Correct Answer Explanation

Down syndrome results from trisomy 21, a chromosomal abnormality caused by nondisjunction. Mendelian disorders arise due to mutations in single genes and follow Mendelian inheritance patterns.

❓ Why Other Options Are Incorrect

Option A) Colour blindness → X-linked Mendelian disorder.
Option C) Haemophilia → X-linked Mendelian disorder.
Option D) Thalassemia → Autosomal Mendelian disorder.

🎯 Strategy

Used: Odd One Out

Option A → Mendelian.
Option B → Chromosomal disorder.
Option C → Mendelian.
Option D → Mendelian.

Final Answer → Down syndrome.

🧠 Memory Trick

📚 → Section/Theme: Chromosomal Disorders

2 The reason for deviation from Mendel's dihybrid cross in T.H. Morgan's experiment is (PYQ 2022 Shift 1)

A Pleiotropy

B Linkage

C Overlapping

D Polygenic Inheritance

💡 Short Explanation

Morgan observed genes inherited together. Linked genes are located on the same chromosome. This caused deviation from independent assortment.

✅ Correct Answer Explanation

T.H. Morgan discovered that some genes do not assort independently because they are located on the same chromosome. Such genes are said to be linked. Linkage results in parental combinations appearing more frequently than expected in Mendel's dihybrid ratio.

❓ Why Other Options Are Incorrect

Option A) Pleiotropy → One gene affects multiple traits.
Option C) Overlapping → Not a recognized genetic principle here.
Option D) Polygenic Inheritance → One trait controlled by multiple genes.

🎯 Strategy

Used: NCERT Recall

Option A → Different concept.
Option B → Correct.
Option C → Incorrect term.
Option D → Different inheritance pattern.

Final Answer → Linkage.

🧠 Memory Trick

📚 → Section/Theme: Linkage and Recombination

3 Given below are two statements:
Statement I: Phenylketonuria is an example of Pleiotropy
Statement II: Affected individuals lack an enzyme which converts phenylalanine into tyrosine (PYQ 2022 Shift 1)

A Both Statement I and Statement II are correct

B Both Statement I and Statement II are incorrect

C Statement I is correct but Statement II is incorrect

D Statement I is incorrect but Statement II is correct

💡 Short Explanation

Phenylketonuria is caused by a single gene mutation. One mutation causes multiple effects. Enzyme deficiency blocks phenylalanine metabolism.

✅ Correct Answer Explanation

Phenylketonuria (PKU) is a classic example of pleiotropy because a mutation in a single gene causes multiple phenotypic effects. The affected person lacks phenylalanine hydroxylase, which normally converts phenylalanine into tyrosine.

❓ Why Other Options Are Incorrect

Option B) Both statements are true.
Option C) Statement II is also correct.
Option D) Statement I is also correct.

🎯 Strategy

Used: NCERT Recall

Option A → Correct.
Option B → Incorrect.
Option C → Statement II true.
Option D → Statement I true.

Final Answer → Option A.

🧠 Memory Trick

📚 → Section/Theme: Pleiotropy

4 Why was Drosophila melanogaster used for studies in Genetics? (PYQ 2022 Shift 1)
(A) They could be cultured easily in the laboratory
(B) They showed many contrasting traits
(C) The generation time was one year
(D) There was clear differentiation of sexes
(E) Very few progeny were produced in a single mating

A (B) and (D) only

B (A) and (D) only

C (B) and (C) only

D (D) and (E) only

💡 Short Explanation

Easily cultured in laboratories. Sexes are easily distinguishable. Short generation time.

✅ Correct Answer Explanation

Drosophila melanogaster became a preferred genetic model because it is easy to culture, has distinct male and female forms, a short life cycle and produces many offspring. Statement C is incorrect because generation time is about two weeks, not one year. Statement E is incorrect because a large number of progeny are produced.

❓ Why Other Options Are Incorrect

Option A) Does not include easy culturing.
Option C) Contains incorrect statement C.
Option D) Contains incorrect statement E.

🎯 Strategy

Used: Elimination

Option A → Incomplete.
Option B → Correct.
Option C → C incorrect.
Option D → E incorrect.

Final Answer → Option B.

🧠 Memory Trick

📚 → Section/Theme: Morgan's Experiments

5 What will be the number of genotypes and phenotypes obtained in F₂ generation when male parent RRYY is crossed with female parent rryy? (PYQ 2023 Shift 1)

A 16 and 4 respectively

B 4 and 16 respectively

C 9 and 4 respectively

D 4 and 9 respectively

💡 Short Explanation

Dihybrid cross. F₂ genotype classes = 9. F₂ phenotype classes = 4.

✅ Correct Answer Explanation

RRYY × rryy produces F₁ RrYy. Selfing F₁ gives a classic Mendelian dihybrid F₂ generation with 9 genotypic combinations and 4 phenotypic classes in a 9:3:3:1 ratio.

❓ Why Other Options Are Incorrect

Option A) 16 refers to Punnett square cells, not genotype count.
Option B) Values reversed.
Option D) Phenotype count incorrect.

🎯 Strategy

Used: Substitution

Option A → Confuses combinations with genotypes.
Option B → Reversed.
Option C → Correct.
Option D → Incorrect phenotype count.

Final Answer → 9 genotypes, 4 phenotypes.

🧠 Memory Trick

📚 → Section/Theme: Dihybrid Cross

📄 Passage

Which of the following genetic disorder is not a type of Mendelian disorder? (PYQ 2023 Shift 1)

A Colour blindness

B Down's syndrome

C Haemophilia

D Thalassemia

💡 Short Explanation

Down syndrome is chromosomal. Mendelian disorders involve single genes. Aneuploidy causes Down syndrome.

✅ Correct Answer Explanation

Down syndrome results from trisomy 21, a chromosomal abnormality caused by nondisjunction. Mendelian disorders arise due to mutations in single genes and follow Mendelian inheritance patterns.

❓ Why Other Options Are Incorrect

Option A) Colour blindness → X-linked Mendelian disorder.
Option C) Haemophilia → X-linked Mendelian disorder.
Option D) Thalassemia → Autosomal Mendelian disorder.

🎯 Strategy

Used: Odd One Out

Option A → Mendelian.
Option B → Chromosomal disorder.
Option C → Mendelian.
Option D → Mendelian.

Final Answer → Down syndrome.

🧠 Memory Trick

📚 → Section/Theme: Chromosomal Disorders

7 Match the following: (PYQ 2023 Shift 1)

List I	List II
A. Human skin colour	I. Multiple allelism
B. Pair of alleles expressing contrasting traits	II. Polygenic inheritance
C. ABO blood group	III. Incomplete dominance
D. Antirrhinum flower colour	IV. Heterozygous

A (A)–(II), (B)–(IV), (C)–(I), (D)–(III)

B (A)–(I), (B)–(III), (C)–(II), (D)–(IV)

C (A)–(II), (B)–(I), (C)–(IV), (D)–(III)

D (A)–(III), (B)–(IV), (C)–(II), (D)–(I)

💡 Short Explanation

Human skin colour → Polygenic inheritance. ABO blood group → Multiple allelism. Antirrhinum flower → Incomplete dominance. Contrasting traits are represented by alleles in heterozygous condition.

✅ Correct Answer Explanation

Human skin colour is controlled by multiple genes and is an example of polygenic inheritance. ABO blood groups are governed by three alleles (IA, IB, i), making it a classic example of multiple allelism. Flower colour in Antirrhinum exhibits incomplete dominance, where heterozygotes show an intermediate phenotype. Contrasting traits are expressed through allelic pairs in heterozygous individuals.

❓ Why Other Options Are Incorrect

Option B → Incorrect matching of skin colour and blood group.
Option C → ABO blood group and heterozygous pair mismatched.
Option D → Multiple incorrect associations.

🎯 Strategy

Used: Option Grouping

Option A → All matches correct.
Option B → Blood group mismatched.
Option C → Multiple errors.
Option D → Multiple errors.

Final Answer → Option A.

🧠 Memory Trick

📚 → Section/Theme: Polygenic Inheritance, Multiple Alleles and Incomplete Dominance

8 The genetic disorder caused due to presence of an additional copy of the chromosome number 21 is: (PYQ 2023 Shift 2)

A Down's syndrome

B Klinefelter syndrome

C Turner's syndrome

D Haemophilia

💡 Short Explanation

Trisomy 21. One extra chromosome 21. Most common chromosomal disorder.

✅ Correct Answer Explanation

Down's syndrome occurs due to nondisjunction resulting in an extra copy of chromosome 21 (47 chromosomes). This condition is known as Trisomy 21.

❓ Why Other Options Are Incorrect

Option B) XXY condition.
Option C) XO condition.
Option D) X-linked Mendelian disorder.

🎯 Strategy

Used: NCERT Recall

Option A → Trisomy 21.
Option B → XXY.
Option C → XO.
Option D → Gene disorder.

Final Answer → Down's syndrome.

🧠 Memory Trick

📚 → Section/Theme: Chromosomal Disorders

9 In a garden pea, the axial flower is dominant to terminal flower. What will be the percentage of offsprings with terminal flowers, when two heterozygous plants are crossed ? (PYQ 2023 Shift 2)

A 25%

B 50%

C 75%

D 0%

💡 Short Explanation

Heterozygous cross = Aa × Aa. Terminal flower is recessive. Recessive phenotype appears in 1/4 offspring.

✅ Correct Answer Explanation

Let axial flower = A (dominant) and terminal flower = a (recessive). Cross: Aa × Aa Genotypic ratio = 1 AA : 2 Aa : 1 aa Terminal flowers appear only in genotype aa. Probability = 1/4 = 25%.

❓ Why Other Options Are Incorrect

Option B) Represents 2/4 offspring.
Option C) Represents dominant phenotype frequency.
Option D) Recessive phenotype definitely appears.

🎯 Strategy

Used: Substitution

Option A → Correct Mendelian ratio.
Option B → Incorrect.
Option C → Dominant phenotype ratio.
Option D → Impossible.

Final Answer → 25%.

🧠 Memory Trick

📚 → Section/Theme: Monohybrid Cross

10 A classical example of mutation arise due to change in a single base pair of DNA is : (PYQ 2023 Shift 2)

A Sickle cell anaemia

B Thalassemia

C Colour blindness

D Cystic fibrosis

💡 Short Explanation

Caused by point mutation. Single nucleotide substitution. Changes glutamic acid to valine.

✅ Correct Answer Explanation

Sickle cell anaemia is caused by a point mutation in the β-globin gene. A single base substitution changes the codon GAG to GUG, resulting in replacement of glutamic acid by valine. This is the classical example of a mutation involving a single base pair change.

❓ Why Other Options Are Incorrect

Option B) Thalassemia → Usually involves deletions or reduced globin synthesis.
Option C) Colour blindness → X-linked recessive disorder but not the classical point mutation example.
Option D) Cystic fibrosis → Commonly due to deletion mutation (ΔF508).

🎯 Strategy

Used: NCERT Recall

Option A → Classic point mutation.
Option B → Different mutation type.
Option C → X-linked disorder.
Option D → Deletion mutation.

Final Answer → Sickle cell anaemia.

🧠 Memory Trick

📚 → Section/Theme: Sickle Cell Anaemia

11 Colour blindness is a ______. (PYQ 2023 Shift 3)

A Sex linked recessive disorder

B Sex linked dominant disorder

C Autosomal recessive disorder

D Autosomal dominant disorder

💡 Short Explanation

Located on X chromosome. Recessive inheritance. More common in males.

✅ Correct Answer Explanation

Colour blindness is an X-linked recessive disorder. Males express the disorder when they inherit the affected X chromosome because they possess only one X chromosome.

❓ Why Other Options Are Incorrect

Option B) Not dominant.
Option C) Not autosomal.
Option D) Not autosomal dominant.

🎯 Strategy

Used: NCERT Recall

Option A → Correct.
Option B → Incorrect.
Option C → Incorrect.
Option D → Incorrect.

Final Answer → Option A.

🧠 Memory Trick

📚 → Section/Theme: Sex-linked Disorders

12 The term used for the association of two genes is: (PYQ 2023 Shift 3)

A Recombination

B Linkage

C Factors

D Inheritance

💡 Short Explanation

Linked genes occur on same chromosome. Tend to be inherited together. Association is called linkage.

✅ Correct Answer Explanation

Linkage refers to the tendency of genes located on the same chromosome to be inherited together because of their physical association. This concept was established through Morgan's experiments.

❓ Why Other Options Are Incorrect

Option A) Recombination separates linked genes.
Option C) General Mendelian term.
Option D) Broad biological process.

🎯 Strategy

Used: NCERT Recall

Option A → Opposite concept.
Option B → Correct.
Option C → General term.
Option D → Broad term.

Final Answer → Linkage.

🧠 Memory Trick

📚 → Section/Theme: Linkage and Recombination

13 If a pink flowered snapdragon plant is crossed with a white flowered snapdragon plant. What will be the phenotype of the progeny? (PYQ 2023 Shift 3)

A Only pink flowered

B Pink, white and red flowered

C Only white flowered

D Pink and white flowered

💡 Short Explanation

Snapdragon exhibits incomplete dominance. Pink flower is heterozygous (Rr). Pink × White gives pink and white offspring.

✅ Correct Answer Explanation

In Snapdragon (Antirrhinum), flower colour shows incomplete dominance. Let: Red = RR White = rr Pink = Rr Cross: Rr × rr Offspring: 50% Rr (Pink) 50% rr (White) Hence, the progeny will have pink and white flowers in a 1:1 ratio.

❓ Why Other Options Are Incorrect

Option A) Only pink flowered → White-flowered offspring are also produced.
Option B) Pink, white and red flowered → Red flowers cannot be produced in this cross.
Option C) Only white flowered → Pink offspring are also formed.

🎯 Strategy

Used: Substitution

Option A → Incomplete outcome.
Option B → Impossible genotype produced.
Option C → Incomplete outcome.
Option D → Matches Punnett cross.

Final Answer → Pink and white flowered.

🧠 Memory Trick

📚 → Section/Theme: Incomplete Dominance

14 Which of the following represents a test cross in which half the offspring is heterozygous and half would be homozygous recessive? (PYQ 2024 Shift 1, 2024 Shift 2)

A TT × tt

B Tt × tt

C Tt × Tt

D tt × tt

💡 Short Explanation

Test cross involves recessive parent. Heterozygote crossed with recessive. Produces 1:1 ratio.

✅ Correct Answer Explanation

A test cross is performed by crossing an individual showing dominant phenotype with a homozygous recessive individual. Tt × tt produces: 50% Tt 50% tt offspring.

❓ Why Other Options Are Incorrect

Option A → Produces all Tt offspring.
Option C → Produces 1:2:1 genotypic ratio.
Option D → Produces all recessive offspring.

🎯 Strategy

Used: Substitution

Option A → All heterozygous.
Option B → 1:1 ratio.
Option C → Mendelian monohybrid ratio.
Option D → No heterozygotes.

Final Answer → Substitution of genotypes.

🧠 Memory Trick

📚 → Class 12 Biology, Chapter 5: Principles of Inheritance and Variation.

15 Which of the following is a recessive trait for garden pea plant ? (PYQ 2024 Shift 1, 2024 Shift 2)

A Round seed

B Constricted pod

C Tall plant

D Violet flower

💡 Short Explanation

Mendel studied seven contrasting traits. Inflated pod is dominant. Constricted pod is recessive.

✅ Correct Answer Explanation

In Mendel's pea plant experiments, pod shape showed complete dominance. Inflated pod shape is dominant whereas constricted pod shape appears only in the homozygous recessive condition.

❓ Why Other Options Are Incorrect

Option A → Round seed is dominant over wrinkled seed.
Option C → Tall plant is dominant over dwarf plant.
Option D → Violet flower is dominant over white flower.

🎯 Strategy

Used: Elimination

Option A → Dominant.
Option B → Recessive.
Option C → Dominant.
Option D → Dominant.

Final Answer → Only constricted pod is recessive.

🧠 Memory Trick

📚 → Class 12 Biology, Chapter 5: Principles of Inheritance and Variation, Mendel's Traits.

16 Which disorder is caused by the substitution of Glutamic acid (Glu) by Valine (Val) at the sixth position of the beta globin chain of the haemoglobin ? (PYQ 2024 Shift 1, 2024 Shift 2)

A Phenylketonuria

B Sickle-cell Anaemia

C Haemophilia

D Thalassemia

💡 Short Explanation

Point mutation disorder. Sixth amino acid altered. Produces abnormal haemoglobin.

✅ Correct Answer Explanation

Sickle-cell anaemia is caused by replacement of glutamic acid with valine at the sixth position of the β-globin chain. This single base substitution results in abnormal HbS, causing sickle-shaped RBCs.

❓ Why Other Options Are Incorrect

Option A → Caused by defective phenylalanine metabolism.
Option C → Blood clotting disorder.
Option D → Reduced synthesis of globin chains.

🎯 Strategy

Used: Contextual/Tonal Matching

Option A → Metabolic disorder.
Option B → Specific amino acid substitution.
Option C → Clotting disorder.
Option D → Quantitative globin defect.

Final Answer → Sickle-cell anaemia.

🧠 Memory Trick

📚 → Class 12 Biology, Chapter 5: Principles of Inheritance and Variation.

17 When one of the parents has 'A' blood group and the other parent has 'O' blood group, then their child can have ______ blood group. (PYQ 2024 Shift 1)

A Only 'A'

B Only 'O'

C Both 'A' and 'O'

D Either 'A' or 'O'

💡 Short Explanation

A parent may be IAIA or IAi. O parent is ii. Offspring can be A or O.

✅ Correct Answer Explanation

If the A-group parent is heterozygous (IAi) and the O-group parent is ii, offspring can be IAi (A group) or ii (O group). Therefore both A and O blood groups are possible.

❓ Why Other Options Are Incorrect

Option A → O group may also occur.
Option B → A group may also occur.
Option C → Incomplete statement; the standard answer is either A or O.

🎯 Strategy

Used: Substitution

Option A → Not always true.
Option B → Not always true.
Option C → Conceptually similar but incomplete.
Option D → Correct genetic possibility.

Final Answer → Option D.

🧠 Memory Trick

📚 → Class 12 Biology, Chapter 5: Principles of Inheritance and Variation.

18 Match the following: (PYQ 2025 Shift 1)

Column A (Character)	Column B (Recessive Trait)
A. Flower colour	I. Green
B. Seed colour	II. Yellow
C. Pod colour	III. Constricted
D. Pod shape	IV. White

A (A) - (II), (B) - (IV), (C) - (I), (D) - (III)

B (A) - (I), (B) - (IV), (C) - (II), (D) - (III)

C (A) - (I), (B) - (II), (C) - (IV), (D) - (III)

D (A) - (IV), (B) - (I), (C) - (II), (D) - (III)

💡 Short Explanation

White flower is recessive. Green seed is recessive. Yellow pod is recessive. Constricted pod is recessive.

✅ Correct Answer Explanation

Mendel identified white flower colour as recessive to violet flower colour. Green seed colour is recessive to yellow seed colour. Yellow pod colour is recessive to green pod colour, and constricted pod shape is recessive to inflated pod shape. Hence the correct matching is A-IV, B-I, C-II and D-III.

❓ Why Other Options Are Incorrect

Option A) (A) - (II), (B) - (IV), (C) - (I), (D) - (III)
Flower and seed traits are incorrectly matched.
Option B) (A) - (I), (B) - (IV), (C) - (II), (D) - (III)
Flower colour and seed colour pairings are incorrect.
Option C) (A) - (I), (B) - (II), (C) - (IV), (D) - (III)
Dominant traits have been wrongly treated as recessive.

🎯 Strategy

Used: NCERT Recall

Option A → Wrong recessive traits.
Option B → Incorrect mapping.
Option D → Matches Mendelian inheritance.

Final Answer → Based on NCERT recall.

🧠 Memory Trick

White-Green-Yellow-Constricted = Recessive Set

📚 Class 12 Biology, Chapter 5 – Principles of Inheritance and Variation, Mendel's Traits

19 Which of the following disorders are the results of aneuploidy? (PYQ 2025 Shift 1)

A (B) and (D) only

B (A), (B) and (C) only

C (A), (B), (C) and (D)

D (A) and (C) only

💡 Short Explanation

Aneuploidy involves chromosome number abnormalities. Down syndrome is trisomy 21. Turner syndrome is monosomy X.

✅ Correct Answer Explanation

Aneuploidy refers to the gain or loss of one or more chromosomes. Down syndrome occurs due to trisomy of chromosome 21 and Turner syndrome results from monosomy of the X chromosome. Haemophilia and thalassemia are gene disorders caused by mutations and are not examples of aneuploidy.

❓ Why Other Options Are Incorrect

B) (A), (B) and (C) only
Haemophilia and thalassemia are not chromosomal disorders.
C) (A), (B), (C) and (D)
Includes gene mutations along with aneuploid conditions.
D) (A) and (C) only
Neither haemophilia nor thalassemia results from aneuploidy.

🎯 Strategy

Used: Option Grouping

Option A → Only aneuploid disorders.
Option B → Includes gene disorders.
Option C → Mixed category.

Final Answer → Based on grouping.

🧠 Memory Trick

Down = Extra Chromosome, Turner = Missing Chromosome

📚 Class 12 Biology, Chapter 5 – Principles of Inheritance and Variation, Chromosomal Disorders

20 Which one of the following options will express intermediate skin colour in an individual? (PYQ 2025 Shift 1)

A AABBCC

B aabbcc

C AaBbCc

D aaBbcc

💡 Short Explanation

Skin colour is polygenic. Intermediate phenotype has balanced alleles. AaBbCc gives medium pigmentation.

✅ Correct Answer Explanation

Human skin colour is controlled by multiple genes. The intensity of pigmentation depends on the number of dominant alleles present. AaBbCc contains three dominant and three recessive alleles, producing an intermediate skin colour between the darkest and lightest extremes.

❓ Why Other Options Are Incorrect

A) AABBCC
Contains maximum dominant alleles and produces the darkest pigmentation.
B) aabbcc
Contains no dominant alleles and produces the lightest pigmentation.
D) aaBbcc
Contains only one dominant allele and does not represent an intermediate condition.

🎯 Strategy

Used: Option Grouping

Option A → Dark extreme.
Option B → Light extreme.
Option C → Intermediate genotype.

Final Answer → Based on polygenic inheritance.

🧠 Memory Trick

3 Dominant + 3 Recessive = Middle Shade

📚 Class 12 Biology, Chapter 5 – Principles of Inheritance and Variation, Polygenic Inheritance

CUET UG Categorised PYQ Biology Unit 4

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