🌸 Chapter 4
Principles of Inheritance and Variation
(MCQs)
🌿
Chapter: Principles of Inheritance and Variation — 100 MCQs with Answers &
Explanations
1. Who is known as the father of
genetics?
A. Darwin
B. Mendel
C. Morgan
D. Lamarck
✅ Answer: B
Explanation: Gregor Johann Mendel is called the Father of Genetics for
discovering the basic laws of inheritance.
2. Mendel conducted experiments on
which plant?
A. Drosophila
B. Pea plant
C. Maize
D. Tobacco
✅ Answer: B
Explanation: He used Pisum sativum (pea plant) for his
hybridization experiments.
3. Which of the following is a
reason Mendel chose pea plant?
A. It is cross-pollinated only
B. It shows clear contrasting traits
C. It has a long life cycle
D. It produces few seeds
✅ Answer: B
Explanation: Pea plant has clearly distinguishable contrasting
characters, essential for inheritance studies.
4. How many pairs of contrasting
traits did Mendel study?
A. 5
B. 6
C. 7
D. 8
✅ Answer: C
Explanation: Mendel studied 7 pairs of contrasting traits such as
tall/dwarf, yellow/green seeds, etc.
5. Which of the following is not
a trait studied by Mendel?
A. Seed shape
B. Pod length
C. Stem height
D. Flower colour
✅ Answer: B
Explanation: Mendel studied seed shape, seed colour, flower colour, pod
colour, pod shape, flower position, and stem height — not pod length.
6. Tallness in pea plant is
controlled by which type of gene?
A. Recessive
B. Dominant
C. Multiple allelic
D. Polygenic
✅ Answer: B
Explanation: Tallness (T) is a dominant trait over dwarfness (t).
7. What is the phenotype ratio in a
monohybrid F₂ generation?
A. 1:2:1
B. 3:1
C. 9:3:3:1
D. 2:1
✅ Answer: B
Explanation: In F₂ generation, tall and dwarf plants appear in 3:1
ratio.
8. What is the genotypic ratio in F₂
generation of monohybrid cross?
A. 1:2:1
B. 3:1
C. 9:3:3:1
D. 2:1:1
✅ Answer: A
Explanation: Genotypes TT, Tt, tt occur in 1:2:1 ratio.
9. Which law explains the purity of
gametes?
A. Law of Dominance
B. Law of Segregation
C. Law of Independent Assortment
D. Law of Recombination
✅ Answer: B
Explanation: Law of segregation states that alleles separate during
gamete formation — hence purity.
10. The physical appearance of an
organism is called:
A. Genotype
B. Phenotype
C. Karyotype
D. Allelotype
✅ Answer: B
Explanation: Phenotype refers to observable characteristics.
11. Tt represents which condition?
A. Homozygous dominant
B. Homozygous recessive
C. Heterozygous
D. Polygenic
✅ Answer: C
Explanation: Tt has two different alleles, hence heterozygous.
12. In dihybrid cross, F₂ phenotypic
ratio is:
A. 1:2:1
B. 9:3:3:1
C. 3:1
D. 2:1:1
✅ Answer: B
Explanation: For two independently assorting traits, Mendel obtained
9:3:3:1 ratio.
13. Which of the following shows
independent assortment?
A. Alleles of the same gene
B. Alleles on same chromosome
C. Genes on different chromosomes
D. None
✅ Answer: C
Explanation: Independent assortment occurs between genes located on
different chromosomes.
14. Test cross is performed between
F₁ hybrid and:
A. Dominant parent
B. Recessive parent
C. F₂ generation
D. Hybrid offspring
✅ Answer: B
Explanation: Test cross = F₁ hybrid × recessive parent (to determine
genotype).
15. Back cross includes:
A. F₁ × recessive
B. F₁ × dominant
C. Both A and B
D. F₁ × F₂
✅ Answer: C
Explanation: Any cross of hybrid (F₁) with either parent is a back
cross.
16. In incomplete dominance, the
phenotype of heterozygote is:
A. Like dominant parent
B. Like recessive parent
C. Intermediate
D. None
✅ Answer: C
Explanation: Incomplete dominance gives intermediate expression — e.g.,
pink flower in Snapdragon.
17. Example of incomplete dominance:
A. Pea plant
B. Snapdragon
C. Drosophila
D. Human blood group
✅ Answer: B
Explanation: In Antirrhinum majus (Snapdragon), red × white gives
pink flowers.
18. Example of co-dominance is:
A. Snapdragon
B. Drosophila
C. ABO blood group
D. Tall × Dwarf
✅ Answer: C
Explanation: In ABO blood group, IA and IB alleles are co-dominant (AB
blood group).
19. How many alleles are involved in
ABO blood group?
A. 2
B. 3
C. 4
D. 1
✅ Answer: B
Explanation: There are three alleles – IA, IB, and i.
20. A gene affecting more than one
trait is:
A. Polygenic
B. Pleiotropic
C. Codominant
D. Linked
✅ Answer: B
Explanation: Pleiotropy means one gene influences multiple traits.
21. Example of pleiotropy:
A. Blood group
B. Colour blindness
C. Sickle cell anaemia
D. Tallness in pea
✅ Answer: C
Explanation: HbS gene affects RBC shape and oxygen capacity.
22. The chromosome theory of
inheritance was proposed by:
A. Mendel
B. Sutton and Boveri
C. Morgan
D. Darwin
✅ Answer: B
Explanation: Sutton and Boveri (1902) related Mendelian factors to
chromosomes.
23. According to chromosomal theory,
genes are located on:
A. Ribosomes
B. Chromosomes
C. Cytoplasm
D. Nucleus only
✅ Answer: B
Explanation: Genes are carried on chromosomes.
24. Who worked on Drosophila
melanogaster?
A. Mendel
B. Morgan
C. Boveri
D. Lamarck
✅ Answer: B
Explanation: T.H. Morgan used fruit fly to study linkage and
recombination.
25. Linkage means:
A. Independent assortment
B. Genes on same chromosome inherited together
C. Mutation of genes
D. Crossing over
✅ Answer: B
Explanation: Linked genes are located close on same chromosome and
inherited together.
26. Recombination leads to:
A. No variation
B. New gene combinations
C. Same parental combination
D. All of these
✅ Answer: B
Explanation: Recombination produces new combinations of traits — a
source of variation.
27. Crossing over occurs during:
A. Prophase I of meiosis
B. Metaphase II
C. Anaphase I
D. Telophase
✅ Answer: A
Explanation: Crossing over takes place during pachytene stage of
prophase I.
28. The process responsible for
exchange of genetic material is:
A. Mutation
B. Segregation
C. Crossing over
D. Translation
✅ Answer: C
Explanation: Crossing over exchanges segments of chromatids —
introducing variation.
29. Sex determination in humans is
of which type?
A. XX–XY
B. ZZ–ZW
C. XO
D. Haplo-diploidy
✅ Answer: A
Explanation: Human males are XY, females are XX.
30. In birds, which sex is
heterogametic?
A. Male
B. Female
✅ Answer: B
Explanation: Female birds (ZW) are heterogametic, males (ZZ) are
homogametic.
31. Honeybee males are produced by:
A. Fertilized egg
B. Unfertilized egg
✅ Answer: B
Explanation: Males (drones) are haploid — from unfertilized eggs
(parthenogenesis).
32. Haemophilia is a:
A. Autosomal dominant
B. Autosomal recessive
C. Sex-linked recessive
D. Sex-linked dominant
✅ Answer: C
Explanation: Haemophilia is X-linked recessive disorder, more common in
males.
33. Colour blindness is due to:
A. Mutation in Y chromosome
B. Mutation in X chromosome
✅ Answer: B
Explanation: Colour blindness is X-linked recessive disorder.
34. In colour blindness, which
colour can’t be distinguished?
A. Blue and green
B. Red and green
✅ Answer: B
Explanation: Red-green colour blindness is most common.
35. Which type of inheritance is
seen in hairy ears in men?
A. X-linked
B. Y-linked
✅ Answer: B
Explanation: Hairy pinna is a holandric (Y-linked) trait — passed father
to son.
36. Which of the following is not a
Mendelian disorder?
A. Sickle cell anaemia
B. Phenylketonuria
C. Down’s syndrome
D. Haemophilia
✅ Answer: C
Explanation: Down’s syndrome is a chromosomal disorder (Trisomy 21), not
single gene defect.
37. Sickle cell anaemia is caused by
mutation in:
A. α-globin gene
B. β-globin gene
✅ Answer: B
Explanation: A single base substitution in β-globin gene (GAG → GTG).
38. Phenylketonuria is due to
absence of enzyme:
A. Phenylalanine hydroxylase
B. Tyrosinase
✅ Answer: A
Explanation: Deficiency prevents conversion of phenylalanine → tyrosine.
39. Down’s syndrome occurs due to:
A. Trisomy 13
B. Trisomy 21
✅ Answer: B
Explanation: Presence of extra chromosome 21.
40. Klinefelter’s syndrome karyotype
is:
A. 45, XO
B. 47, XXY
✅ Answer: B
Explanation: Extra X chromosome in male (XXY).
41. Turner’s syndrome karyotype is:
A. 45, XO
B. 47, XXY
✅ Answer: A
Explanation: Female with single X chromosome (XO).
42. Which law fails in linkage?
A. Law of Dominance
B. Law of Independent Assortment
✅ Answer: B
Explanation: Linked genes do not assort independently.
43. The unit of inheritance is:
A. Gene
B. Chromosome
✅ Answer: A
Explanation: Gene is the functional unit controlling a specific
character.
44. A cross between red and white
flowers gives pink offspring. It is an example of:
A. Co-dominance
B. Incomplete dominance
✅ Answer: B
45. IA IB genotype expresses which blood
group?
A. A
B. B
C. AB
✅ Answer: C
Explanation: Both alleles express equally → AB group.
46. Recessive allele expresses when:
A. Dominant present
B. In homozygous condition
✅ Answer: B
47. Which organism did Morgan use to
prove linkage?
A. Pea
B. Drosophila
✅ Answer: B
48. The term “gene” was coined by:
A. Mendel
B. Johannsen
✅ Answer: B
49. Alleles are:
A. Identical genes
B. Alternative forms of a gene
✅ Answer: B
50. 9:3:3:1 ratio is obtained in:
A. Monohybrid
B. Dihybrid
✅ Answer: B
51. The cross between F₁ hybrid and
recessive parent is used to determine:
A. Dominance
B. Genotype of F₁
C. Phenotype of F₂
D. Independent assortment
✅ Answer: B
Explanation: A test cross helps determine whether F₁ is homozygous or
heterozygous.
52. The progeny obtained by crossing
F₁ with recessive parent will show ratio:
A. 1:1
B. 3:1
C. 1:2:1
D. 9:3:3:1
✅ Answer: A
Explanation: Test cross gives 1:1 phenotypic ratio when F₁ is
heterozygous.
53. Which of the following does not
follow Mendel’s law of independent assortment?
A. Linked genes
B. Genes on different chromosomes
✅ Answer: A
Explanation: Linked genes are inherited together and do not assort
independently.
54. Which of the following is true
for incomplete dominance?
A. One allele is completely dominant
B. Intermediate phenotype appears
✅ Answer: B
Explanation: Heterozygote shows blending effect (pink flower in
Snapdragon).
55. Co-dominance differs from
incomplete dominance because:
A. Both alleles express equally
B. One allele is silent
✅ Answer: A
Explanation: In co-dominance (e.g., blood group AB), both alleles express
independently.
56. Phenotypic ratio of incomplete
dominance in F₂ generation is:
A. 3:1
B. 1:2:1
✅ Answer: B
Explanation: Same as genotypic ratio since intermediate phenotype
appears.
57. The number of alleles involved
in human ABO blood group system is:
A. 2
B. 3
✅ Answer: B
Explanation: Three alleles IA, IB, and i determine four blood groups.
58. The IA and IB alleles in ABO
system are:
A. Recessive
B. Co-dominant
✅ Answer: B
Explanation: IA and IB express equally when present together (AB group).
59. The inheritance of ABO blood
group was explained by:
A. Mendel
B. Landsteiner
✅ Answer: B
Explanation: Karl Landsteiner discovered the ABO blood group system.
60. The principle of independent
assortment was verified by:
A. Monohybrid cross
B. Dihybrid cross
✅ Answer: B
Explanation: Dihybrid cross shows independent segregation of two
characters.
61. Chromosomal theory of
inheritance connects:
A. Chromosomes and environment
B. Chromosomes and genes
✅ Answer: B
Explanation: Sutton and Boveri proposed that genes are located on
chromosomes.
62. The term “linkage” was first
used by:
A. Morgan
B. Bateson and Punnett
✅ Answer: B
Explanation: Bateson and Punnett observed coupling and repulsion in
sweet pea.
63. Complete linkage means:
A. Genes always separate
B. Genes always inherited together
✅ Answer: B
Explanation: No recombination occurs; genes are transmitted as a unit.
64. In humans, the total number of
autosomes is:
A. 22 pairs
B. 23 pairs
✅ Answer: A
Explanation: Humans have 22 pairs of autosomes and 1 pair of sex
chromosomes.
65. The female sex chromosome
combination in humans is:
A. XX
B. XY
✅ Answer: A
66. Male heterogamety is found in:
A. Humans
B. Birds
✅ Answer: A
Explanation: Males (XY) produce two types of gametes.
67. Female heterogamety is found in:
A. Humans
B. Birds
✅ Answer: B
Explanation: Females (ZW) produce two types of eggs.
68. Haplo-diploid system is seen in:
A. Drosophila
B. Honeybee
✅ Answer: B
Explanation: Male bees are haploid, females are diploid.
69. Number of chromosomes in haploid
male honeybee is:
A. 16
B. 32
✅ Answer: A
Explanation: Males are haploid with 16 chromosomes.
70. Female honeybee develops from:
A. Fertilized egg
B. Unfertilized egg
✅ Answer: A
Explanation: Fertilized egg → diploid → female.
71. Haemophilia was first discovered
by:
A. Landsteiner
B. Hoppe-Seyler
C. John Otto
D. Karl Correns
✅ Answer: C
Explanation: John Otto described haemophilia in 1803.
72. Haemophilia is more common in
males because:
A. X-linked recessive
B. Y-linked
✅ Answer: A
Explanation: Males have one X; mutation on X causes disease as there’s
no backup allele.
73. A carrier female for colour
blindness will have which genotype?
A. Xá´ºXá´º
B. XᴺXᶜ
C. XᶜXᶜ
✅ Answer: B
Explanation: XᴺXᶜ female is phenotypically normal but carries the
defective allele.
74. Colour blindness is due to
defect in:
A. Cones
B. Rods
✅ Answer: A
Explanation: Colour perception is due to cone cells.
75. Y-linked traits are transmitted
to:
A. Sons only
B. Daughters only
✅ Answer: A
Explanation: Y chromosome passes only from father to son.
76. A man with colour blindness will
pass the gene to:
A. All sons
B. All daughters
✅ Answer: B
Explanation: Daughters receive the father’s X chromosome carrying the
mutant gene.
77. A cross between colour-blind man
and carrier woman produces:
A. 50% colour-blind sons
B. All colour-blind sons
✅ Answer: A
Explanation: Sons get X from mother → 50% chance if mother is carrier.
78. Down’s syndrome results due to:
A. Trisomy of 21
B. Monosomy of X
✅ Answer: A
79. Turner’s syndrome individuals
are:
A. Female
B. Male
✅ Answer: A
Explanation: Turner’s females have XO genotype.
80. Klinefelter’s syndrome
individuals are:
A. Male
B. Female
✅ Answer: A
Explanation: Extra X chromosome in male → XXY → sterile male.
81. Which of the following is not a
chromosomal disorder?
A. Down’s syndrome
B. Phenylketonuria
✅ Answer: B
Explanation: Phenylketonuria is a single gene disorder.
82. Gene for sickle cell anaemia is:
A. Autosomal recessive
B. Autosomal dominant
✅ Answer: A
83. The abnormality in sickle cell
anaemia is due to:
A. Base substitution
B. Base deletion
✅ Answer: A
Explanation: Substitution of A → T changes Glu to Val.
84. Individuals with sickle cell
trait (heterozygous) are:
A. Diseased
B. Normal but resistant to malaria
✅ Answer: B
Explanation: Heterozygotes are carriers and malaria-resistant.
85. Phenylketonuria leads to
accumulation of:
A. Phenylalanine
B. Tyrosine
✅ Answer: A
86. Which of the following genotypes
represents a female carrier for haemophilia?
A. Xá´´Xá´´
B. Xá´´XÊ°
✅ Answer: B
Explanation: One normal and one defective allele → carrier female.
87. Pedigree analysis is used for:
A. Studying evolution
B. Studying inheritance of traits in family
✅ Answer: B
88. In pedigree chart, a shaded
square represents:
A. Affected male
B. Normal male
✅ Answer: A
Explanation: Square = male, shaded = affected.
89. A carrier female for X-linked
disorder and normal male — percentage of affected sons?
A. 0%
B. 50%
✅ Answer: B
90. The disorder caused due to lack
of clotting factor VIII:
A. Sickle cell anaemia
B. Haemophilia A
✅ Answer: B
91. Chromosomal aberration refers
to:
A. Mutation in base pair
B. Change in chromosome number or structure
✅ Answer: B
92. Trisomy means:
A. Addition of one chromosome
B. Deletion of one chromosome
✅ Answer: A
Explanation: Trisomy = 2n + 1.
93. Monosomy means:
A. 2n – 1
B. 2n + 1
✅ Answer: A
Explanation: Missing one chromosome.
94. Which of the following is an
example of monosomy?
A. Turner’s syndrome
B. Down’s syndrome
✅ Answer: A
95. The condition of having extra
chromosome 18 is called:
A. Edwards syndrome
B. Patau syndrome
✅ Answer: A
96. Chromosome number in Down’s
syndrome patient:
A. 46
B. 47
✅ Answer: B
Explanation: Extra chromosome 21 → total 47.
97. Which of the following
statements is incorrect?
A. Linked genes follow independent assortment
B. Haemophilia is X-linked disorder
✅ Answer: A
98. The ratio 9:3:3:1 represents:
A. Dihybrid cross
B. Co-dominance
✅ Answer: A
99. The gene controlling ABO blood
group is located on:
A. Chromosome 9
B. Chromosome 11
✅ Answer: A
Explanation: ABO locus is on chromosome 9.
100. The number of linkage groups in
humans equals:
A. 23
B. 22
✅ Answer: A
Explanation: Linkage groups = number of chromosome pairs → 23 in humans.
