Chapter 5: Principles of Inheritance and Variation – MCQs
🟢 Part 1: Principles of Inheritance and Variation (Q1–Q25)
Q1. Who is considered the father of genetics?
a) Charles Darwin
b) Gregor Mendel
c) Hugo de Vries
d) Alfred Wallace
Answer: b) Gregor Mendel
Explanation: Mendel is regarded as the father of genetics for his experiments on pea plants and laws of inheritance.
Q2. Mendel used which plant for his hybridization experiments?
a) Maize
b) Pea (Pisum sativum)
c) Sunflower
d) Wheat
Answer: b) Pea (Pisum sativum)
Explanation: Mendel selected pea plants because they had contrasting traits, short life cycle, and were easy to cross.
Q3. Which of the following is a monohybrid cross?
a) Tt × Tt
b) TtRr × TtRr
c) TTRR × ttrr
d) AaBb × AaBb
Answer: a) Tt × Tt
Explanation: Monohybrid cross involves inheritance of a single trait, e.g., tall vs dwarf in peas.
Q4. In Mendel’s monohybrid cross, the F2 phenotypic ratio is:
a) 9:3:3:1
b) 3:1
c) 1:2:1
d) 1:1
Answer: b) 3:1
Explanation: In F2 generation of monohybrid cross, 75% dominant and 25% recessive phenotypes appear.
Q5. In Mendel’s dihybrid cross, the F2 phenotypic ratio is:
a) 3:1
b) 9:3:3:1
c) 1:2:1
d) 1:1
Answer: b) 9:3:3:1
Explanation: Dihybrid cross (two traits) in F2 shows a 9:3:3:1 ratio of phenotypes due to independent assortment.
Q6. Which of the following represents Mendel’s law of segregation?
a) Factors occur in pairs but separate during gamete formation
b) Two alleles assort independently
c) Dominant alleles mask recessive ones
d) Alleles blend together
Answer: a) Factors occur in pairs but separate during gamete formation
Explanation: Law of segregation states alleles separate during gamete formation and unite randomly at fertilization.
Q7. Which law explains the inheritance of two independent traits?
a) Law of dominance
b) Law of segregation
c) Law of independent assortment
d) Law of linkage
Answer: c) Law of independent assortment
Explanation: Mendel’s law of independent assortment states that different traits assort independently during gamete formation.
Q8. The physical appearance of an organism is called:
a) Genotype
b) Phenotype
c) Allele
d) Locus
Answer: b) Phenotype
Explanation: Phenotype refers to the observable characteristics of an organism, while genotype is the genetic makeup.
Q9. Which term refers to alternative forms of a gene?
a) Locus
b) Allele
c) Chromatid
d) Homologous chromosome
Answer: b) Allele
Explanation: Alleles are alternate forms of a gene controlling the same trait, e.g., T (tall) and t (dwarf).
Q10. A heterozygous tall plant (Tt) is crossed with a dwarf plant (tt). The ratio of tall to dwarf in progeny is:
a) 1:1
b) 3:1
c) 9:3:3:1
d) 2:1
Answer: a) 1:1
Explanation: Tt × tt gives 50% tall (Tt) and 50% dwarf (tt).
Q11. Which of the following shows incomplete dominance?
a) Snapdragon flower color
b) Pea seed shape
c) Human blood group
d) Hemophilia
Answer: a) Snapdragon flower color
Explanation: In snapdragons, red (RR) × white (rr) gives pink (Rr), an example of incomplete dominance.
Q12. Which phenomenon is seen in blood group inheritance?
a) Incomplete dominance
b) Co-dominance
c) Segregation
d) Polygenic inheritance
Answer: b) Co-dominance
Explanation: In ABO blood group, IA and IB alleles express equally, showing co-dominance.
Q13. A cross between red and white flowers gives pink flowers. This is due to:
a) Mutation
b) Co-dominance
c) Incomplete dominance
d) Independent assortment
Answer: c) Incomplete dominance
Explanation: Intermediate phenotype arises in incomplete dominance.
Q14. Which blood group is called the universal donor?
a) A
b) B
c) AB
d) O
Answer: d) O
Explanation: Blood group O has no antigens, can be donated to all.
Q15. Which blood group is the universal recipient?
a) A
b) B
c) AB
d) O
Answer: c) AB
Explanation: Blood group AB has no antibodies, can receive from all groups.
Q16. Which of the following diseases is sex-linked?
a) Diabetes
b) Hemophilia
c) Tuberculosis
d) Malaria
Answer: b) Hemophilia
Explanation: Hemophilia is X-linked recessive, more common in males.
Q17. Color blindness is caused by defect in:
a) Chromosome 21
b) X chromosome
c) Y chromosome
d) Mitochondria
Answer: b) X chromosome
Explanation: Color blindness is X-linked recessive, affecting red-green color perception.
Q18. Which disorder is due to nondisjunction of chromosome 21?
a) Klinefelter’s syndrome
b) Down’s syndrome
c) Turner’s syndrome
d) Hemophilia
Answer: b) Down’s syndrome
Explanation: Trisomy of chromosome 21 causes Down’s syndrome (47 chromosomes).
Q19. Which condition is represented as 47, XXY?
a) Turner’s syndrome
b) Klinefelter’s syndrome
c) Down’s syndrome
d) Super female
Answer: b) Klinefelter’s syndrome
Explanation: Males with an extra X chromosome (XXY) develop Klinefelter’s syndrome.
Q20. Which condition is represented as 45, XO?
a) Down’s syndrome
b) Turner’s syndrome
c) Klinefelter’s syndrome
d) Super male
Answer: b) Turner’s syndrome
Explanation: Females with a missing X chromosome (XO) develop Turner’s syndrome.
Q21. Which of the following disorders is caused by mutation in a single gene?
a) Down’s syndrome
b) Sickle cell anemia
c) Turner’s syndrome
d) Klinefelter’s syndrome
Answer: b) Sickle cell anemia
Explanation: Point mutation in the β-globin gene causes sickle-shaped RBCs.
Q22. In sickle cell anemia, glutamic acid is replaced by:
a) Alanine
b) Valine
c) Glycine
d) Proline
Answer: b) Valine
Explanation: A point mutation replaces glutamic acid with valine in the hemoglobin β-chain.
Q23. Which type of inheritance is shown in skin color in humans?
a) Monogenic
b) Polygenic
c) Sex-linked
d) Dominant
Answer: b) Polygenic
Explanation: Skin color is controlled by multiple genes → polygenic inheritance.
Q24. Which genetic disorder is caused by absence of clotting factor VIII?
a) Thalassemia
b) Hemophilia
c) Color blindness
d) Sickle cell anemia
Answer: b) Hemophilia
Explanation: Hemophilia A is caused by deficiency of clotting factor VIII.
Q25. Thalassemia is caused due to defect in:
a) Chromosome number
b) Hemoglobin synthesis
c) Blood pressure regulation
d) Immune system
Answer: b) Hemoglobin synthesis
Explanation: Thalassemia is caused by reduced/absent synthesis of hemoglobin α or β chains.
🟢 Part 2: Genetics and Evolution – Principles of Inheritance and Variation (Q26–Q50)
Q26. Who coined the term “gene”?
a) Gregor Mendel
b) Wilhelm Johannsen
c) Hugo de Vries
d) Thomas Hunt Morgan
Answer: b) Wilhelm Johannsen
Explanation: Johannsen coined the term “gene” in 1909 for hereditary units.
Q27. The chromosomal theory of inheritance was proposed by:
a) Mendel
b) Sutton and Boveri
c) Darwin
d) Morgan
Answer: b) Sutton and Boveri
Explanation: Sutton and Boveri (1902) related Mendel’s factors to chromosomes, giving chromosomal theory of inheritance.
Q28. Which scientist proved that genes are located on chromosomes?
a) Sutton
b) Darwin
c) Morgan
d) Wallace
Answer: c) Morgan
Explanation: Thomas Hunt Morgan’s work on Drosophila proved genes are carried on chromosomes.
Q29. The smallest unit of inheritance is:
a) Chromosome
b) Gene
c) DNA molecule
d) Nucleotide
Answer: b) Gene
Explanation: Gene is the basic unit of inheritance, carrying instructions for traits.
Q30. Who discovered linkage in Drosophila?
a) Mendel
b) Morgan
c) Johannsen
d) Sutton
Answer: b) Morgan
Explanation: Morgan observed linked genes in Drosophila, deviating from independent assortment.
Q31. Crossing over occurs in which stage of meiosis?
a) Prophase I
b) Metaphase I
c) Anaphase II
d) Telophase II
Answer: a) Prophase I
Explanation: Homologous chromosomes exchange genetic material during pachytene of prophase I.
Q32. The unit of crossing over is:
a) Cistron
b) Map unit (centimorgan)
c) Chromatid
d) Allele
Answer: b) Map unit (centimorgan)
Explanation: 1 map unit (1 cM) represents 1% recombination frequency between two linked genes.
Q33. The frequency of crossing over is used to:
a) Determine gene expression
b) Construct genetic maps
c) Detect mutations
d) Determine chromosome number
Answer: b) Construct genetic maps
Explanation: Recombination frequency helps locate genes on chromosomes.
Q34. Which scientist introduced the concept of mutation theory?
a) Mendel
b) Hugo de Vries
c) Darwin
d) Morgan
Answer: b) Hugo de Vries
Explanation: De Vries proposed mutation theory based on Oenothera lamarckiana (evening primrose).
Q35. The abnormality due to presence of an extra chromosome is called:
a) Deletion
b) Aneuploidy
c) Euploidy
d) Mutation
Answer: b) Aneuploidy
Explanation: Aneuploidy refers to gain/loss of specific chromosomes (e.g., trisomy).
Q36. The individual with 45 chromosomes (XO) suffers from:
a) Down’s syndrome
b) Turner’s syndrome
c) Klinefelter’s syndrome
d) Thalassemia
Answer: b) Turner’s syndrome
Explanation: Females with 45 chromosomes (XO) develop Turner’s syndrome.
Q37. If a child inherits blood group A from father and blood group B from mother, the child’s blood group will be:
a) A
b) B
c) AB
d) O
Answer: c) AB
Explanation: IA and IB alleles are co-dominant, leading to blood group AB.
Q38. Which of the following is an autosomal recessive disorder?
a) Sickle cell anemia
b) Hemophilia
c) Color blindness
d) Turner’s syndrome
Answer: a) Sickle cell anemia
Explanation: Sickle cell anemia is caused by a recessive mutation in the β-globin gene.
Q39. In a test cross, a heterozygous plant is crossed with:
a) Homozygous dominant
b) Homozygous recessive
c) Heterozygous
d) Self-crossed
Answer: b) Homozygous recessive
Explanation: Test cross determines genotype by crossing with homozygous recessive.
Q40. A cross between two individuals differing in two traits is called:
a) Monohybrid cross
b) Dihybrid cross
c) Test cross
d) Back cross
Answer: b) Dihybrid cross
Explanation: Involves inheritance of two traits simultaneously, e.g., seed color and seed shape.
Q41. Back cross involves crossing F1 hybrid with:
a) Dominant parent only
b) Recessive parent only
c) Either dominant or recessive parent
d) Another F1
Answer: c) Either dominant or recessive parent
Explanation: Back cross = F1 × any parent (dominant or recessive).
Q42. Which of the following shows polygenic inheritance?
a) Hemophilia
b) Skin color in humans
c) Pea seed shape
d) Blood group
Answer: b) Skin color in humans
Explanation: Polygenic inheritance involves multiple genes controlling a trait, e.g., human skin color.
Q43. In dihybrid cross, recombinants are formed due to:
a) Mutation
b) Independent assortment
c) Segregation
d) Polyploidy
Answer: b) Independent assortment
Explanation: Independent assortment of alleles leads to new combinations (recombinants).
Q44. The number of linkage groups in humans is:
a) 22
b) 23
c) 24
d) 46
Answer: b) 23
Explanation: Linkage groups = number of chromosome pairs; humans have 23 pairs.
Q45. A female carrier for hemophilia marries a normal male. Probability of hemophilic son is:
a) 0%
b) 25%
c) 50%
d) 100%
Answer: c) 50%
Explanation: Carrier mother (XHXh) × Normal father (XHY) → 50% sons (XhY) hemophilic.
Q46. Which of the following describes pleiotropy?
a) One gene controlling multiple traits
b) Multiple genes controlling one trait
c) Two alleles blending
d) Genes located on same chromosome
Answer: a) One gene controlling multiple traits
Explanation: Pleiotropy is when one gene influences several traits, e.g., sickle cell gene.
Q47. Thalassemia is caused by defect in:
a) Protein synthesis
b) Hemoglobin chain production
c) Enzyme activity
d) DNA replication
Answer: b) Hemoglobin chain production
Explanation: Thalassemia is due to reduced or absent synthesis of α or β chains of hemoglobin.
Q48. The pink flower color in snapdragon is an example of:
a) Incomplete dominance
b) Co-dominance
c) Polygenic inheritance
d) Mutation
Answer: a) Incomplete dominance
Explanation: Heterozygotes show intermediate phenotype (pink) between red and white.
Q49. Who rediscovered Mendel’s work in 1900?
a) Hugo de Vries, Correns, Tschermak
b) Morgan and Sutton
c) Darwin and Wallace
d) Johannsen and de Vries
Answer: a) Hugo de Vries, Correns, Tschermak
Explanation: Three scientists independently rediscovered Mendel’s laws in 1900.
Q50. Which term describes the position of a gene on a chromosome?
a) Allele
b) Locus
c) Linkage group
d) Centromere
Answer: b) Locus
Explanation: Locus refers to the fixed position of a gene on a chromosome.
🟢 Part 3: Genetics and Evolution – Principles of Inheritance and Variation (Q51–Q75)
Q51. In a dihybrid cross, which of the following phenotypes is least frequent in F2?
a) Parental combinations
b) Recombinant combinations
c) Dominant traits combination
d) Recessive traits combination
Answer: b) Recombinant combinations
Explanation: Recombinants occur due to independent assortment and are less frequent compared to parental types.
Q52. If a heterozygous tall plant (Tt) is self-crossed, the genotypic ratio in F2 is:
a) 1:2:1
b) 3:1
c) 9:3:3:1
d) 2:1
Answer: a) 1:2:1
Explanation: Tt × Tt produces TT:Tt:tt in the ratio 1:2:1.
Q53. The phenotypic ratio of incomplete dominance in F2 generation is:
a) 3:1
b) 9:3:3:1
c) 1:2:1
d) 1:1
Answer: c) 1:2:1
Explanation: In incomplete dominance, F2 shows 1 homozygous dominant : 2 heterozygous : 1 homozygous recessive phenotype.
Q54. Which inheritance pattern is shown by multiple alleles?
a) Blood groups in humans
b) Flower color in snapdragon
c) Sickle cell anemia
d) Skin color in humans
Answer: a) Blood groups in humans
Explanation: ABO blood group system is controlled by three alleles – IA, IB, and i.
Q55. Which law of inheritance explains why two traits can be inherited independently?
a) Law of segregation
b) Law of dominance
c) Law of independent assortment
d) Chromosomal theory
Answer: c) Law of independent assortment
Explanation: Independent assortment allows alleles of different genes to assort independently.
Q56. Crossing over increases:
a) Linkage
b) Mutation rate
c) Variation
d) Homozygosity
Answer: c) Variation
Explanation: Crossing over produces new combinations of alleles, enhancing genetic variation.
Q57. In which phase of meiosis does independent assortment occur?
a) Prophase I
b) Metaphase I
c) Anaphase I
d) Telophase II
Answer: b) Metaphase I
Explanation: Independent assortment occurs when homologous chromosomes align randomly at the equatorial plate.
Q58. Genes present on the same chromosome form a:
a) Gene pool
b) Linkage group
c) Locus
d) Genotype
Answer: b) Linkage group
Explanation: Genes on the same chromosome are said to be linked, forming a linkage group.
Q59. Who first used Drosophila melanogaster for genetic studies?
a) Mendel
b) Morgan
c) Sutton
d) Hugo de Vries
Answer: b) Morgan
Explanation: Thomas Hunt Morgan used fruit fly to study linkage and sex-linked inheritance.
Q60. A dihybrid test cross shows phenotypic ratio:
a) 9:3:3:1
b) 3:1
c) 1:1:1:1
d) 2:1
Answer: c) 1:1:1:1
Explanation: Test cross of dihybrid (AaBb × aabb) produces four types of offspring equally.
Q61. Which disorder is caused by trisomy of chromosome 21?
a) Turner’s syndrome
b) Down’s syndrome
c) Klinefelter’s syndrome
d) Edwards’ syndrome
Answer: b) Down’s syndrome
Explanation: Trisomy 21 (47 chromosomes) results in Down’s syndrome.
Q62. If both alleles of a gene are expressed equally in heterozygotes, it is called:
a) Incomplete dominance
b) Co-dominance
c) Polygenic inheritance
d) Pleiotropy
Answer: b) Co-dominance
Explanation: In co-dominance, both alleles contribute equally to phenotype (e.g., AB blood group).
Q63. Which blood group genotype is heterozygous?
a) IAIA
b) IBIB
c) IAi
d) ii
Answer: c) IAi
Explanation: IAi produces blood group A but carries a recessive i allele.
Q64. A disease in which RBCs become sickle-shaped is due to:
a) Hemophilia
b) Thalassemia
c) Sickle cell anemia
d) Leukemia
Answer: c) Sickle cell anemia
Explanation: Mutation in hemoglobin β-chain causes sickle-shaped red blood cells.
Q65. Which chromosome is affected in Turner’s syndrome?
a) X chromosome missing
b) Y chromosome missing
c) Trisomy 21
d) Extra X chromosome
Answer: a) X chromosome missing
Explanation: Turner’s syndrome results from monosomy (45, XO) in females.
Q66. Which of the following disorders is polygenic?
a) Hemophilia
b) Diabetes mellitus
c) Color blindness
d) Thalassemia
Answer: b) Diabetes mellitus
Explanation: Diabetes is influenced by multiple genes and environment → polygenic disorder.
Q67. Inheritance of tallness in pea plants is an example of:
a) Dominant trait
b) Recessive trait
c) Incomplete dominance
d) Polygenic inheritance
Answer: a) Dominant trait
Explanation: Tallness (T) is dominant over dwarfness (t) in pea plants.
Q68. Who coined the term “linkage”?
a) Sutton
b) Boveri
c) Morgan
d) Bateson
Answer: d) Bateson
Explanation: William Bateson first used the term “linkage” to describe genes inherited together.
Q69. What is the condition of a person with 47 chromosomes including XXY?
a) Turner’s syndrome
b) Down’s syndrome
c) Klinefelter’s syndrome
d) Normal male
Answer: c) Klinefelter’s syndrome
Explanation: XXY condition leads to Klinefelter’s syndrome in males.
Q70. A woman with blood group O can have a child with blood group AB if father’s blood group is:
a) A
b) B
c) AB
d) Not possible
Answer: d) Not possible
Explanation: O mother (ii) cannot contribute IA or IB, so child cannot be AB.
Q71. Independent assortment does not hold true if:
a) Genes are linked
b) Genes are on different chromosomes
c) Crossing over occurs
d) Traits are dominant
Answer: a) Genes are linked
Explanation: Linked genes are inherited together, violating law of independent assortment.
Q72. In which inheritance does one gene control more than one trait?
a) Polygenic inheritance
b) Pleiotropy
c) Co-dominance
d) Linkage
Answer: b) Pleiotropy
Explanation: One gene influencing multiple traits = pleiotropy (e.g., sickle cell gene).
Q73. If both parents are carriers of thalassemia, probability of affected child is:
a) 0%
b) 25%
c) 50%
d) 75%
Answer: b) 25%
Explanation: Cross (Tt × Tt) → TT: Tt: Tt: tt = 1:2:1; 25% chance of thalassemia.
Q74. Which of the following is an example of sex-limited trait?
a) Baldness in humans
b) Color blindness
c) Hemophilia
d) Sickle cell anemia
Answer: a) Baldness in humans
Explanation: Baldness is sex-influenced, more common in males due to hormonal effect.
Q75. Which type of inheritance is human height an example of?
a) Polygenic inheritance
b) Co-dominance
c) Incomplete dominance
d) Sex-linked inheritance
Answer: a) Polygenic inheritance
Explanation: Human height is controlled by many genes and environment, hence polygenic.
🟢 Part 4: Genetics and Evolution – Principles of Inheritance and Variation (Q76–Q100)
Q76. Which of the following is an example of multiple alleles?
a) Hemophilia
b) ABO blood group
c) Color blindness
d) Sickle cell anemia
Answer: b) ABO blood group
Explanation: ABO system has three alleles – IA, IB, and i, which is a classic case of multiple alleles.
Q77. Which phenomenon explains variation produced during gamete formation?
a) Mutation
b) Independent assortment
c) Linkage
d) Gene flow
Answer: b) Independent assortment
Explanation: Independent assortment of chromosomes during meiosis produces genetic variation.
Q78. In which inheritance pattern does phenotype resemble neither parent?
a) Co-dominance
b) Incomplete dominance
c) Polygenic inheritance
d) Pleiotropy
Answer: b) Incomplete dominance
Explanation: Heterozygote shows an intermediate phenotype, e.g., pink flowers in snapdragon.
Q79. Which of the following disorders is caused by absence of clotting factor VIII?
a) Thalassemia
b) Hemophilia A
c) Sickle cell anemia
d) Color blindness
Answer: b) Hemophilia A
Explanation: Hemophilia A is due to absence of clotting factor VIII, leading to excessive bleeding.
Q80. Which scientist proposed that genes are located linearly on chromosomes?
a) Darwin
b) Sutton
c) Morgan
d) Mendel
Answer: c) Morgan
Explanation: Morgan’s experiments on Drosophila showed linear arrangement of genes on chromosomes.
Q81. Which term describes an organism with two identical alleles for a trait?
a) Homozygous
b) Heterozygous
c) Hemizygous
d) Dominant
Answer: a) Homozygous
Explanation: Organisms with identical alleles (TT or tt) are homozygous.
Q82. Who coined the term “chromosome”?
a) Flemming
b) Boveri
c) Sutton
d) Waldeyer
Answer: d) Waldeyer
Explanation: Heinrich Waldeyer coined the term “chromosome” in 1888.
Q83. Which genetic disorder is caused by substitution mutation?
a) Thalassemia
b) Sickle cell anemia
c) Turner’s syndrome
d) Down’s syndrome
Answer: b) Sickle cell anemia
Explanation: Substitution of valine for glutamic acid in hemoglobin β-chain leads to sickle cell anemia.
Q84. The probability of obtaining a homozygous recessive in a monohybrid cross (Tt × Tt) is:
a) 25%
b) 50%
c) 75%
d) 100%
Answer: a) 25%
Explanation: Cross produces TT:Tt:tt = 1:2:1 → 25% homozygous recessive (tt).
Q85. Which of the following is aneuploidy?
a) Trisomy 21
b) Polyploidy in plants
c) Triploidy (3n)
d) Tetraploidy (4n)
Answer: a) Trisomy 21
Explanation: Aneuploidy involves addition/loss of one chromosome, as in Down’s syndrome (trisomy 21).
Q86. Which of the following pairs is mismatched?
a) Color blindness – X-linked
b) Hemophilia – Y-linked
c) Down’s syndrome – Trisomy 21
d) Klinefelter’s syndrome – 47, XXY
Answer: b) Hemophilia – Y-linked
Explanation: Hemophilia is X-linked, not Y-linked.
Q87. A normal couple has a color-blind daughter. What must be true?
a) Father is color blind
b) Mother is carrier
c) Both a and b
d) Neither a nor b
Answer: c) Both a and b
Explanation: For daughter to be color blind (XcXc), father must be color blind (XcY) and mother must be at least a carrier (XcX).
Q88. In humans, the sex of a child is determined by:
a) X chromosome of mother
b) Y chromosome of father
c) X chromosome of father
d) Both parents equally
Answer: b) Y chromosome of father
Explanation: Sperm contributes X or Y chromosome, deciding female (XX) or male (XY) child.
Q89. Which scientist introduced the concept of gene mapping using crossing over frequency?
a) Mendel
b) Sturtevant
c) Morgan
d) Hugo de Vries
Answer: b) Sturtevant
Explanation: Alfred Sturtevant (student of Morgan) constructed first genetic map using recombination frequencies.
Q90. Which of the following is an example of polygenic inheritance?
a) Skin color in humans
b) ABO blood group
c) Hemophilia
d) Sickle cell anemia
Answer: a) Skin color in humans
Explanation: Polygenic traits are controlled by multiple genes and show continuous variation.
Q91. What is the probability of a carrier mother (XcX) and normal father (XY) having a color-blind son?
a) 25%
b) 50%
c) 75%
d) 100%
Answer: b) 50%
Explanation: Sons inherit X from mother and Y from father → 50% chance of XcY (color blind).
Q92. Which of the following is an example of pleiotropy?
a) Human skin color
b) ABO blood group
c) Sickle cell anemia
d) Eye color in Drosophila
Answer: c) Sickle cell anemia
Explanation: A single gene mutation causes multiple effects – abnormal RBC shape, anemia, resistance to malaria.
Q93. Which of the following statements is true for polygenic inheritance?
a) Traits are discontinuous
b) Controlled by a single gene
c) Shows continuous variation
d) Shows 3:1 ratio
Answer: c) Shows continuous variation
Explanation: Polygenic traits (e.g., height, skin color) show a wide range of phenotypes (continuous variation).
Q94. The human genome contains approximately:
a) 10,000 genes
b) 25,000 genes
c) 1,00,000 genes
d) 1,000 genes
Answer: b) 25,000 genes
Explanation: Human genome project estimated about 20,000–25,000 functional genes.
Q95. Which of the following is a sex-influenced trait?
a) Color blindness
b) Hemophilia
c) Baldness in humans
d) Thalassemia
Answer: c) Baldness in humans
Explanation: Baldness is influenced by sex hormones; dominant in males, recessive in females.
Q96. Which disease is caused by an autosomal dominant mutation?
a) Sickle cell anemia
b) Huntington’s chorea
c) Thalassemia
d) Color blindness
Answer: b) Huntington’s chorea
Explanation: Huntington’s disease is an autosomal dominant neurological disorder.
Q97. Which chromosome number anomaly is associated with mental retardation and flat facial features?
a) 45, XO
b) 47, XXY
c) Trisomy 21
d) 46, XY
Answer: c) Trisomy 21
Explanation: Down’s syndrome (Trisomy 21) shows characteristic facial features and intellectual disability.
Q98. Which of the following is not a Mendelian disorder?
a) Hemophilia
b) Thalassemia
c) Sickle cell anemia
d) Down’s syndrome
Answer: d) Down’s syndrome
Explanation: Down’s syndrome is chromosomal, while others are single-gene Mendelian disorders.
Q99. Which process leads to exchange of genetic material between homologous chromosomes?
a) Mutation
b) Crossing over
c) Independent assortment
d) Fertilization
Answer: b) Crossing over
Explanation: During prophase I of meiosis, homologous chromosomes exchange segments, producing recombinants.
Q100. Which concept best explains why linked genes are usually inherited together?
a) Crossing over
b) Mutation theory
c) Law of independent assortment
d) Chromosomal theory of inheritance
Answer: d) Chromosomal theory of inheritance
Explanation: Linked genes are located close together on the same chromosome, so they are inherited together.
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