60. What is the term for different forms of the same gene?
[DSSSB Assistant Superintendent, 6 July 2026 (Shift 2)]
(a) Chromosomes
(b) Traits
(c) Genotypes
(d) Alleles
Answer: (d) Alleles
Explanation: Alleles are alternative versions of a particular gene at the same chromosomal locus. A diploid organism generally receives one allele from each parent. Different allelic combinations help explain inherited variation, such as contrasting seed colours in pea plants.
59. Assertion (A): In polygenic inheritance, each gene has a major and easily identifiable phenotypic effect.
Reason (R): Polygenes usually exert only slight effects individually.
Select the correct answer.
[UPHESC Assistant Professor (Botany), 18 April 2026 (Shift 2)]
(a) Both A and R are true, and R explains A.
(b) A is false, but R is true.
(c) A is true, but R is false.
(d) Both A and R are true, but R does not explain A.
Answer: (b) A is false, but R is true.
Explanation: Polygenic traits arise from the combined action of many genes, each usually contributing a small effect. Human height and skin pigmentation illustrate such inheritance. The assertion wrongly attributes a large individual effect to every contributing gene, while the reason is correct.
58. Which scientist is honoured with the title “Father of Genetics”?
[DSSSB MTS, 5 March 2026 (Shift 3)]
(a) Mendel
(b) Lamarck
(c) Franklin
(d) Darwin
Answer: (a) Mendel
Explanation: Gregor Johann Mendel uncovered fundamental inheritance patterns by crossing garden pea plants and counting offspring with contrasting traits. His evidence established segregation and independent assortment. Darwin studied evolution, Lamarck proposed acquired-character inheritance, and Rosalind Franklin contributed to elucidating DNA structure.
57. What was Mendel’s contribution to genetics?
[RRB Group D, 30 December 2025 (Shift 2)]
(a) Theory of Evolution
(b) Discovery of DNA
(c) Inheritance of Acquired Traits
(d) Laws of Inheritance
Answer: (d) Laws of Inheritance
Explanation: Mendel experimentally showed that hereditary factors are transmitted in predictable patterns, developing laws of dominance, segregation and independent assortment. His approach relied on controlled crosses and counting pea-plant offspring. He did not discover the molecular structure of DNA.
56. What is the main purpose of creating DNA copies during reproduction?
[RRB Group D, 30 December 2025 (Shift 1)]
(a) To change the structure of cells
(b) To make organisms immune to diseases
(c) To produce identical twins
(d) To pass genetic information to offspring
Answer: (d) To pass genetic information to offspring
Explanation: DNA replication provides offspring or daughter cells with genetic instructions inherited from the parent. The copying mechanism is usually accurate but can introduce small variations. Those variations, when heritable, help create diversity on which evolutionary processes can act.
55. How many contrasting characters were used by Mendel to formulate the laws of inheritance?
[RRB Group D, 21 December 2025 (Shift 1)]
(a) 5
(b) 7
(c) 8
(d) 4
Answer: (b) 7
Explanation: Mendel examined seven pairs of contrasting traits in garden pea plants, including tall versus dwarf stems and round versus wrinkled seeds. Carefully following these discrete differences across generations enabled him to discover consistent numerical patterns of inheritance.
54. Why did Mendel use true-breeding plants as parents in his crosses?
[RRB Group D, 14 December 2025 (Shift 1)]
(a) To get a large number of plants quickly
(b) To grow them in similar soil conditions
(c) To study environmental effects on plant growth
(d) To study inheritance patterns
Answer: (d) To study inheritance patterns
Explanation: True-breeding lines consistently reproduce the same observable trait when self-pollinated, making their inherited characteristics predictable. Crossing contrasting pure lines let Mendel determine how parental factors combine in hybrids and how recessive traits reappear in subsequent generations.
53. Which of the following is NOT a trait Mendel studied in pea plants?
[RRB Group D, 9 December 2025 (Shift 1)]
(a) Plant height
(b) Flower position
(c) Seed shape
(d) Leaf size
Answer: (d) Leaf size
Explanation: Mendel chose seven readily distinguishable features, including plant height, seed shape, seed colour, pod shape, pod colour, flower colour and flower position. Leaf size was not among his selected contrasting characters, making it the exception in these options.
52. Which of the following can be considered a reason for Mendel’s success in formulating laws of inheritance?
[RRB Group D, 8 December 2025 (Shift 1)]
(a) He had supernatural power.
(b) He was a monk.
(c) He had knowledge of mathematics.
(d) He was a well-trained scientist.
Answer: (c) He had knowledge of mathematics.
Explanation: Mendel used systematic counting and mathematical ratios to interpret large numbers of pea-plant offspring. Quantitative treatment revealed regular segregation patterns instead of relying only on visual impressions. His mathematical analysis was especially important for identifying Mendelian inheritance laws.
51. Assertion (A): Mendel chose pea plants because they were easy to grow and showed distinct contrasting traits.
Reason (R): Pea plants reproduce asexually, allowing Mendel to control crosses easily.
[RRB Group D, 5 December 2025 (Shift 3)]
(a) A is false, but R is true.
(b) A is true, but R is false.
(c) Both A and R are true, and R explains A.
(d) Both A and R are true, but R does not explain A.
Answer: (b) A is true, but R is false.
Explanation: Garden peas are sexually reproducing flowering plants capable of self-pollination and controlled cross-pollination, not asexual reproduction. Their short generation time and clear alternative traits were useful. Therefore, the assertion correctly explains their experimental suitability, but the reason is false.
50. In Mendel’s experiments, when he crossed a tall (TT) pea plant with a short (tt) pea plant, what did he observe in the first generation (F1)?
[RRB Group D, 28 November 2025 (Shift 3)]
(a) Half were tall and half were short.
(b) All were tall.
(c) All were of medium height.
(d) All were short.
Answer: (b) All were tall.
Explanation: Every F1 offspring has genotype Tt, receiving T from the tall parent and t from the dwarf parent. Because tallness is dominant in Mendel’s chosen pea lines, all F1 plants appear tall even though they carry the recessive allele.
49. The observable expression of the genotype is known as __________.
[DSSSB TGT (Natural Science), 6 September 2025 (Shift 1)]
(a) Genotype
(b) Genome
(c) Gene
(d) Phenotype
Answer: (d) Phenotype
Explanation: Phenotype refers to measurable or observable features of an organism, such as flower colour or body height. It arises through interaction between genetic makeup and environment. Genotype denotes inherited alleles, whereas a genome comprises the organism’s overall genetic material.
48. The process by which traits are passed from parents to offspring is known as __________.
[RRB NTPC (Undergraduate) CBT-I, 28 August 2025 (Shift 3)]
(a) Mutation
(b) Heredity
(c) Hybridisation
(d) Linkage
Answer: (b) Heredity
Explanation: Heredity is the transmission of characteristics between generations through inherited genetic material. A mutation changes genetic information; hybridisation involves crossing different types; and linkage describes genes tending to travel together. Only heredity names the general parent-to-offspring transfer of traits.
47. What is the study of heredity and variation called?
[RRB NTPC (Undergraduate) CBT-I, 18 August 2025 (Shift 3)]
(a) Evolution
(b) Mutation
(c) Genetics
(d) Biology
Answer: (c) Genetics
Explanation: Genetics investigates genes, the transmission of traits, and differences among individuals. It includes inheritance patterns and molecular mechanisms. Biology is the broader study of life; mutation refers to alteration of genetic material, and evolution concerns population changes over generations.
46. A single gene can often have multiple effects on the phenotype of an organism, affecting a number of apparently unrelated traits. This phenomenon is known as:
[MH SET (Life Sciences), 2025]
(a) Epistasis
(b) Polygenic inheritance
(c) Pleiotropy
(d) Epigenetic effect
Answer: (c) Pleiotropy
Explanation: Pleiotropy occurs when one gene influences several distinct traits. Sickle-cell disease is a familiar example, affecting red cells and multiple organs. It contrasts with polygenic inheritance, in which many genes contribute to one characteristic, and epistasis, involving interactions between genes.
45. Which structure within the nucleus contains genetic information in the form of DNA?
[SSC MTS, 11 November 2024 (Shift 1)]
(a) Ribosome
(b) Chromosome
(c) Nucleolus
(d) Vacuole
Answer: (b) Chromosome
Explanation: Chromosomes consist principally of DNA packaged with proteins and contain many genes. In eukaryotic cells, they occupy the nucleus and become particularly conspicuous during cell division. Ribosomes synthesize proteins, while nucleoli participate in ribosome production rather than serving as chromosomes.
44. Which specific chemical can be applied to achieve staining of chromosomes?
[SSC MTS, 23 October 2024 (Shift 1)]
(a) Ethanol
(b) Hydrochloric acid
(c) Acetocarmine
(d) Methanol
Answer: (c) Acetocarmine
Explanation: Acetocarmine stains chromosomal material and helps make dividing-cell chromosomes visible under a microscope. It is commonly used in plant cytology and chromosome preparations. The alternative chemicals listed are not the standard chromosomal stain required by this question.
43. Select the INCORRECT statement.
[SSC MTS, 9 October 2024 (Shift 3)]
(a) Functional segments of DNA are called genes.
(b) Chromatin forms rod-shaped chromosomes when a cell approaches division.
(c) Chromosomes are composed of DNA and carbohydrates.
(d) DNA carries information needed to build and organise cells.
Answer: (c) Chromosomes are composed of DNA and carbohydrates.
Explanation: Eukaryotic chromosomes consist of DNA associated primarily with proteins, especially histones, not carbohydrates as a principal structural component. Genes are functional DNA sequences, and chromatin condenses into visible chromosomes for cell division. Accordingly, the third statement is incorrect.
42. Which of the given options is rod-shaped, carries genetic information, is visible especially during cell division and is present in the nucleus?
[SSC MTS, 8 October 2024 (Shift 2)]
(a) Chromosomes
(b) Lysosomes
(c) Ribosomes
(d) Cytoplasm
Answer: (a) Chromosomes
Explanation: During mitosis, chromatin condenses into distinct chromosomes that can appear rod-shaped under a microscope. Chromosomes carry genes and ensure orderly distribution of DNA to daughter cells. Lysosomes digest cellular material, ribosomes translate RNA, and cytoplasm is the surrounding cellular region.
41. Which of Mendel’s laws states that a diploid organism passes one allele for a trait to its offspring, so the offspring receive one allele from each parent?
[SSC CHSL Tier-I, 5 July 2024 (Shift 2)]
(a) Law of independent assortment
(b) Law of paired factor
(c) Law of dominance
(d) Law of segregation
Answer: (d) Law of segregation
Explanation: The law of segregation states that the two alleles at a gene locus separate during gamete formation. Each gamete normally receives one allele, and fertilisation combines parental contributions. This explains the characteristic 3:1 phenotypic ratio of a standard monohybrid F2 cross.
40. The interaction between nonallelic genes at different loci in which one gene masks the phenotypic expression of another is called:
[SSC CHSL Tier-I, 5 July 2024 (Shift 1)]
(a) Epistasis
(b) Linkage
(c) Incomplete inheritance
(d) Complete inheritance
Answer: (a) Epistasis
Explanation: Epistasis describes an interaction in which one gene alters or masks the expression of another gene at a different locus. It can modify classic Mendelian ratios. Linkage instead concerns physical proximity of genes on the same chromosome and their tendency to be inherited together.
39. In which year did Wilhelm Johannsen coin the term “gene” for Mendelian units of heredity?
[SSC CHSL Tier-I, 4 July 2024 (Shift 2)]
(a) 1920
(b) 1910
(c) 1900
(d) 1909
Answer: (d) 1909
Explanation: Wilhelm Johannsen introduced the term gene in 1909, giving Mendel’s proposed hereditary factors a lasting name. Johannsen also distinguished genotype from phenotype. The terminology helped separate inherited constitution from observable traits and became foundational to modern genetics.
38. Mendel proposed the law of independent assortment on the basis of __________.
[SSC CHSL Tier-I, 1 July 2024 (Shift 4)]
(a) Dihybrid crosses
(b) Alleles
(c) Monohybrid crosses
(d) Genes
Answer: (a) Dihybrid crosses
Explanation: A dihybrid cross follows two different traits simultaneously. Mendel observed an approximately 9:3:3:1 phenotypic ratio among F2 offspring when the relevant alleles assort independently. The rule generally applies to unlinked genes, not necessarily genes tightly linked on one chromosome.
37. “Photo 51” refers to an image of:
[UPSC CDS General Knowledge, 21 April 2024]
(a) A crater on the Moon
(b) DNA molecules
(c) The virus responsible for COVID-19
(d) The virus responsible for the common cold
Answer: (b) DNA molecules
Explanation: Photo 51 is a famous X-ray diffraction photograph of DNA made by Rosalind Franklin and Raymond Gosling. Its characteristic pattern provided important structural evidence for the DNA double helix, the molecule that stores and transmits hereditary information.
36. In most prokaryotes, the chromosome number is:
[UPSC NDA General Ability Test, 21 April 2024]
(a) 4
(b) 3
(c) 2
(d) 1
Answer: (d) 1
Explanation: Many bacteria possess one principal circular chromosome carrying essential hereditary genes, although exceptions exist and some species have multiple replicons. Unlike eukaryotes, prokaryotes lack a membrane-bound nucleus; their chromosomal DNA generally occupies a nucleoid region.
35. Consider:
(1) DNA replication occurs when chromatin opens up;
(2) Chromatin condenses into rod-shaped chromosomes before cell division;
(3) Prokaryotes and eukaryotes divide by the same process.
Which statements are correct?
[UPSC NDA General Ability Test, 21 April 2024]
(a) 1 only
(b) 1 and 2 only
(c) 1, 2 and 3
(d) 3 only
Answer: (b) 1 and 2 only
Explanation: DNA becomes accessible for replication as chromatin reorganises, and it condenses into discrete chromosomes during eukaryotic division. Prokaryotes generally divide by binary fission, unlike mitosis and meiosis in eukaryotes. Thus, the first two statements are correct, but the third is not.
34. Among the following diseases, which one is NOT inherited?
[SSC CGL Tier-II, 26 October 2023]
(a) Down syndrome
(b) Cystic fibrosis
(c) Malaria
(d) Muscular dystrophy
Answer: (c) Malaria
Explanation: Malaria is a parasitic infection transmitted by mosquitoes and is not itself a genetic disease. Cystic fibrosis and many muscular dystrophies result from inherited mutations. Down syndrome is a chromosomal disorder, usually arising from a new nondisjunction event rather than direct parental inheritance.
33. Which process is called “reduction division” because it halves the chromosome number to form sperm and eggs?
[SSC MTS, 6 September 2023 (Shift 1)]
(a) Amitosis
(b) Meiosis
(c) Cytokinesis
(d) Karyokinesis
Answer: (b) Meiosis
Explanation: Meiosis reduces the chromosome complement from diploid to haploid when gametes form. Subsequent fertilisation reunites two haploid sets. Genetic recombination and independent assortment during meiosis also create variation, allowing sexually produced offspring to differ from their parents and siblings.
32. Chromosomes are composed of DNA and:
[UPSC CDS General Knowledge, 3 September 2023]
(a) Lipids
(b) Vitamins
(c) Proteins
(d) Carbohydrates
Answer: (c) Proteins
Explanation: Eukaryotic chromosomes consist of long DNA molecules wrapped around histone and other proteins. This packaging stabilises genetic material and helps regulate gene expression and chromosome segregation. Lipids and carbohydrates are not the principal partners forming the chromosome’s structural framework.
31. The two important features of sexual reproduction in higher organisms that create genetic diversity in offspring are:
[UPSC NDA-II General Ability, 3 September 2023]
(a) Mitosis and fertilisation
(b) Meiosis and fertilisation
(c) Mitosis and binary fission
(d) Meiosis and conjugation
Answer: (b) Meiosis and fertilisation
Explanation: Meiosis shuffles genes through crossing over and random chromosome assortment, producing genetically varied gametes. Fertilisation then combines genetic material from two parents in unpredictable pairings. Their combined effects explain much of the diversity seen among offspring produced sexually.
30. In a sexually reproducing organism, which statement is appropriate for both parent and offspring?
[UPSC NDA-II General Ability, 3 September 2023]
(a) Chromosome number increases but DNA content remains constant.
(b) Both chromosome number and DNA content remain constant.
(c) Chromosome number decreases but DNA content remains constant.
(d) Both chromosome number and DNA content decrease.
Answer: (b) Both chromosome number and DNA content remain constant.
Explanation: Meiosis halves the chromosome number in gametes, and fertilisation restores the normal diploid complement in each new generation. For a species with stable ploidy, parents and offspring ordinarily retain the same characteristic chromosome number and broadly similar total nuclear DNA content.
29. Match: (i) Gaucher disease, (ii) Hunter syndrome, (iii) Tay–Sachs disease, (iv) phenylketonuria
with (a) phenylalanine hydroxylase, (b) hexosaminidase A, (c) iduronate-2-sulfatase, (d) glucocerebrosidase.
[SSC CGL Tier-I, 26 July 2023 (Shift 4)]
(a) i-a, ii-b, iii-c, iv-d
(b) i-b, ii-c, iii-a, iv-d
(c) i-d, ii-c, iii-b, iv-a
(d) i-b, ii-a, iii-d, iv-c
Answer: (c) i-d, ii-c, iii-b, iv-a
Explanation: Each genetic metabolic disorder follows deficiency of a characteristic enzyme: Gaucher disease involves glucocerebrosidase, Hunter syndrome iduronate-2-sulfatase, Tay–Sachs disease hexosaminidase A, and phenylketonuria phenylalanine hydroxylase. The specified order is therefore d, c, b, a.
28. In which year did Joe Hin Tjio publish the finding that 2n = 46 is the exact number of human chromosomes?
[SSC CGL Tier-I, 20 July 2023 (Shift 4)]
(a) 1950
(b) 1952
(c) 1956
(d) 1960
Answer: (c) 1956
Explanation: The correct human somatic chromosome count of 46 was reported in 1956 through work by Joe Hin Tjio and Albert Levan. It overturned the earlier assumption of 48 and became crucial for clinical cytogenetics and the recognition of chromosomal disorders.
27. The process of determining the relative positions of genes on a chromosome is called:
[BPSC Teacher Recruitment Examination (TRE-1), August 2023]
(a) Genome walking
(b) Chromosome walking
(c) Gene mapping
(d) More than one of the above
Answer: (c) Gene mapping
Explanation: Gene mapping identifies the position and relative order of genes on chromosomes. Genetic linkage, recombination frequencies and molecular markers can help locate genes. Such maps are useful in understanding inherited diseases, plant breeding and distinguishing chromosome regions associated with particular traits.
26. The human ABO blood-group system is an example of:
[MPPSC Forest Service Examination, 2023]
(a) Epistatic genes
(b) Multiple alleles
(c) Complementation
(d) Polygenic inheritance
Answer: (b) Multiple alleles
Explanation: The ABO locus has three common alleles in populations: Iᴬ, Iᴮ and i. An individual inherits only two, but the existence of more than two allele forms at the same gene locus demonstrates multiple allelism. Iᴬ and Iᴮ additionally show codominance.
25. What would have happened if Mendel had NOT studied the F2 generation?
[RRB Group D, 11 October 2022 (Shift 3)]
(a) He would not have studied multiple characters.
(b) He would not have identified dominant traits.
(c) He would not have obtained hybrid plants.
(d) He would not have discovered that recessive traits are not lost.
Answer: (d) He would not have discovered that recessive traits are not lost.
Explanation: Recessive characters disappear phenotypically in a standard F1 monohybrid generation but reappear among F2 offspring after hybrid selfing. Seeing the F2 result established that hidden hereditary factors persisted rather than being destroyed or permanently blended in the first generation.
24. Identify the true statement about chromosomes carried by human sperm.
[RRB Group D, 6 October 2022 (Shift 2)]
(a) X-bearing sperm have 22 chromosomes and Y-bearing sperm have 23.
(b) X-bearing sperm have 23 chromosomes and Y-bearing sperm have 22.
(c) Both X-bearing and Y-bearing sperm have 23 chromosomes.
(d) Both X-bearing and Y-bearing sperm have 22 chromosomes.
Answer: (c) Both X-bearing and Y-bearing sperm have 23 chromosomes.
Explanation: A normal human sperm contains 22 autosomes and one sex chromosome, either X or Y, making 23 in total. The identity of the sex chromosome changes, not the total number. An egg also carries 23 chromosomes, including an X.
23. Which statement about Mendel’s pea-plant experiments is INCORRECT?
[RRB Group D, 29 September 2022 (Shift 2)]
(a) Tallness and shortness reappearing in F2 showed both traits were inherited by F1.
(b) All plants in the F2 generation obtained from F1 tall plants were tall.
(c) Mendel studied contrasting traits such as round and wrinkled seeds.
(d) Crossing pure tall and pure dwarf plants gave tall F1 offspring.
Answer: (b) All plants in the F2 generation obtained from F1 tall plants were tall.
Explanation: When heterozygous tall F1 pea plants self-pollinate, recessive dwarf offspring return in F2. The expected phenotypic ratio is approximately three tall to one dwarf, not all tall. This observation helped establish segregation of paired hereditary factors.
22. A normal human body cell has 46 chromosomes. How many chromosomes does a normal human gamete have?
[RRB Group D, 20 September 2022 (Shift 3)]
(a) 22
(b) 44
(c) 46
(d) 23
Answer: (d) 23
Explanation: Human somatic cells are generally diploid, containing 23 chromosome pairs. Meiosis generates haploid sperm or eggs with one member of each pair, totalling 23. Fertilisation then combines two haploid gametes to restore 46 chromosomes in the zygote.
21. Which of the following statements is INCORRECT?
[RRB Group D, 19 September 2022 (Shift 2)]
(a) All children inherit a Y chromosome from their mother.
(b) Human chromosomes do not all exist as identical matching pairs.
(c) In some animals, including certain snails, individuals can change sex.
(d) Sex can be determined by different mechanisms in different species.
Answer: (a) All children inherit a Y chromosome from their mother.
Explanation: Human mothers normally have XX sex chromosomes and contribute X-bearing eggs. Consequently, they do not transmit Y chromosomes to children. A Y chromosome, if present, is contributed by the father. Other species may have different sex-determining systems.
20. How many pairs of sex chromosomes are present in humans?
[RRB Group D, 16 September 2022 (Shift 3)]
(a) 2 pairs
(b) 1 pair
(c) 3 pairs
(d) 4 pairs
Answer: (b) 1 pair
Explanation: A normal human diploid complement has 23 chromosome pairs: 22 pairs of autosomes and one pair of sex chromosomes. Typical females have XX and typical males have XY. Sex chromosomes influence sexual development and carry numerous additional genes.
19. One of the contrasting pairs of characters studied by Mendel was __________.
[RRB Group D, 15 September 2022 (Shift 2)]
(a) Blue and white flowers
(b) Purple and white flowers
(c) Yellow and purple flowers
(d) White and yellow flowers
Answer: (b) Purple and white flowers
Explanation: Mendel examined purple versus white flower colour in garden peas as one of his seven pairs of contrasting traits. Purple flower colour was dominant over white in his experimental lines. Tracking such differences across generations revealed predictable inheritance patterns.
18. In Mendel’s experiment, when F1 plants were self-pollinated, what was the genotypic ratio in F2?
[RRB Group D, 2 September 2022 (Shift 1)]
(a) 1 : 2 : 3
(b) 1 : 2 : 1
(c) 2 : 2 : 1
(d) 3 : 2 : 1
Answer: (b) 1 : 2 : 1
Explanation: Selfing a heterozygous monohybrid, such as Tt × Tt, produces TT, Tt, Tt and tt combinations. Their genotypic ratio is 1:2:1, whereas with complete dominance the corresponding phenotypes show a 3:1 dominant-to-recessive ratio.
17. How is the chromosome number maintained from one generation to another in sexually reproducing organisms?
[RRB Group D, 30 August 2022 (Shift 2)]
(a) Halving of chromosomes during gamete formation
(b) Doubling of chromosomes during zygote formation
(c) Halving of chromosomes during zygote formation
(d) Doubling of chromosomes during gamete formation
Answer: (a) Halving of chromosomes during gamete formation
Explanation: Meiosis reduces the chromosome number by half when gametes form, preventing doubling in successive generations. Fusion of two haploid gametes at fertilisation restores the diploid set. The balancing of reduction and restoration maintains the typical species chromosome number.
16. In human males, sex chromosomes are XY. What is the difference between them?
[RRB Group D, 24 August 2022 (Shift 2)]
(a) There is no difference in size.
(b) Y has more genes than X.
(c) X is larger, whereas Y is smaller.
(d) Y is larger, whereas X is smaller.
Answer: (c) X is larger, whereas Y is smaller.
Explanation: The human X chromosome is considerably larger and contains many more genes than the Y chromosome. Although both participate in sex-chromosome inheritance, the Y carries genes important for male sexual development, including the SRY region, and is much smaller.
15. DNA barcoding can be a tool to:
(1) assess the age of a plant or animal,
(2) distinguish species that look alike,
(3) identify undesirable animal or plant material in processed foods.
Which statements are correct?
[UPSC Civil Services Preliminary Examination, 5 June 2022]
(a) 1 only
(b) 3 only
(c) 1 and 2 only
(d) 2 and 3 only
Answer: (d) 2 and 3 only
Explanation: DNA barcoding compares selected DNA sequences against reference libraries to identify organisms. It can distinguish similar-looking species and reveal biological ingredients in processed products. This technique does not directly measure an individual organism’s chronological age, making statements two and three correct.
14. Har Gobind Khorana won a Nobel Prize for his contribution in __________.
[RRB NTPC CBT-I, 19 March 2021 (Shift 2)]
(a) Mathematics
(b) Physics
(c) Chemistry
(d) Genetics
Answer: (d) Genetics
Explanation: Har Gobind Khorana shared the 1968 Nobel Prize in Physiology or Medicine for research deciphering the genetic code and its role in protein synthesis. His work clarified how nucleotide sequences specify amino acids, establishing a critical link between genes and proteins.
13. Change in the base sequence within a gene is called:
[UPPSC Preliminary Examination, 2020]
(a) Mutation
(b) Cloning
(c) Fission
(d) Breeding
Answer: (a) Mutation
Explanation: A mutation is a change in nucleotide sequence within DNA. A gene-level mutation can alter a protein, change regulation or have no noticeable effect. Such changes may arise during replication or following exposure to mutagens and can be inherited when present in germ cells.
12. Which characteristics of the genetic code are true?
(i) It is generally universal;
(ii) it uses triplets of nucleotide bases;
(iii) it is non-overlapping, unambiguous and comma-less;
(iv) it includes start and stop codons.
[MPPSC State Service Preliminary Examination, 2020]
(a) i, ii and iv only
(b) i, iii and iv only
(c) i, ii and iii only
(d) All of the above
Answer: (d) All of the above
Explanation: Codons are nucleotide triplets, read sequentially during translation. Most organisms use a nearly universal code with defined initiation and termination signals. Each codon specifies one amino acid or a stop signal, though multiple codons can specify the same amino acid.
11. Consider:
(1) Genetic changes can be introduced in the cells that produce eggs or sperm.
(2) A person’s genome can be edited before birth at an early embryonic stage.
(3) Human induced pluripotent stem cells can be injected into a pig embryo.
Which are correct?
[UPSC Civil Services Preliminary Examination, 2020]
(a) 1 only
(b) 2 and 3 only
(c) 2 only
(d) 1, 2 and 3
Answer: (d) 1, 2 and 3
Explanation: Modern biotechnology can alter germline precursor cells, edit early embryos and introduce human pluripotent cells into animal embryos for experimental research. These possibilities raise major ethical and regulatory questions. All three describe techniques or approaches considered biologically feasible.
10. Chromosome number in any species:
[Chhattisgarh PSC (CGPSC) State Service Preliminary Examination, 2019]
(a) Increases with age
(b) Decreases with age
(c) Is constant
(d) Increases with body weight
Answer: (c) Is constant
Explanation: Each species generally has a characteristic chromosome complement in ordinary diploid body cells. Its count is maintained across generations through meiosis and fertilisation. Chromosome number can differ in gametes or due to genetic abnormalities, but it does not normally rise with age or weight.
9. Regarding genetically modified mustard developed in India, consider:
(1) Its bacterial genes give broad pest resistance.
(2) Its introduced genes enable cross-pollination and hybridisation.
(3) It was developed jointly by IARI and Punjab Agricultural University.
Which statements are correct?
[UPSC Civil Services Preliminary Examination, 2018]
(a) 1 and 3 only
(b) 2 only
(c) 2 and 3 only
(d) 1, 2 and 3
Answer: (b) 2 only
Explanation: The barnase–barstar genetic system helps enable hybrid seed production in mustard. The introduced traits were not designed as general protection against many insect pests, and the project was associated with Delhi University researchers rather than the institutional pairing stated.
8. “Particulate theory of inheritance” was proposed by:
[WBCS Preliminary Examination, 2017]
(a) Charles Darwin
(b) Gregor Johann Mendel
(c) Hermann Muller
(d) T. H. Morgan
Answer: (b) Gregor Johann Mendel
Explanation: Mendel proposed that discrete hereditary factors, rather than permanently blending parental characteristics, pass from one generation to another. His pea-plant results demonstrated that recessive traits can remain hidden in hybrids and reappear later, supporting particulate inheritance.
7. The phenotypic ratio of a Mendelian dihybrid cross is:
[WBCS Preliminary Examination, 2015]
(a) 9 : 3 : 3 : 1
(b) 1 : 1 : 1 : 1
(c) 3 : 4 : 3 : 1
(d) 1 : 2 : 1 : 1
Answer: (a) 9 : 3 : 3 : 1
Explanation: For two independently assorting genes showing complete dominance, selfing AaBb hybrids produces four phenotype classes in the ratio 9:3:3:1. The pattern combines two 3:1 monohybrid ratios and requires sufficient independence between the inheritance of the two traits.
6. Who gave the term “genetics”?
[RPSC Senior Teacher Grade II (Science), 2015]
(a) Mendel
(b) Morgan
(c) Bateson
(d) Boveri
Answer: (c) Bateson
Explanation: British biologist William Bateson popularised the term genetics for the scientific study of heredity and variation. Mendel established the experimental laws of inheritance, whereas Thomas Hunt Morgan contributed important evidence for chromosome linkage and the genetic role of chromosomes.
5. Assertion (A): DNA fingerprinting can help establish paternity and identify suspects in criminal investigations.
Reason (R): Small biological samples such as hair, dried blood and semen can provide adequate DNA for analysis.
[Rajasthan RAS Preliminary Examination, 2013]
(a) Both A and R are true, and R explains A.
(b) Both A and R are true, but R does not explain A.
(c) A is true, but R is false.
(d) A is false, but R is true.
Answer: (a) Both A and R are true, and R explains A.
Explanation: DNA profiling compares highly variable genetic markers between biological samples and reference individuals. Properly collected samples containing suitable cells can establish identity or biological relationships with statistical support. Thus, the availability of DNA from trace material explains the technique’s forensic usefulness.
4. Knowing the relative positions of genes on a chromosome can help:
(1) identify livestock pedigrees,
(2) understand the causes of all human diseases,
(3) develop disease-resistant animal breeds.
Which are correct?
[UPSC Civil Services Preliminary Examination, 2011]
(a) 1 and 2 only
(b) 2 only
(c) 1 and 3 only
(d) 1, 2 and 3
Answer: (c) 1 and 3 only
Explanation: Gene maps help trace inherited markers through pedigrees and select desirable traits, including disease resistance, in animal breeding. However, not every human disease is caused solely by identifiable genetic factors; environmental and infectious causes also contribute. Therefore, the second claim is too broad.
3. Genetics deals with:
[BPSC Preliminary Examination (53rd–55th), 2011]
(a) Mendel’s laws only
(b) Organic evolution only
(c) DNA structure only
(d) Heredity and variations
Answer: (d) Heredity and variations
Explanation: Genetics encompasses how traits pass between generations and why genetically related organisms differ. Its scope includes molecular DNA structure, Mendelian laws, chromosomal inheritance and variation. None of the narrower alternatives captures the entire field, making heredity and variation the comprehensive description.
2. Genome mapping relates to:
[UPPSC Preliminary Examination, 2002]
(a) Blood grouping
(b) Mapping of genes
(c) Mapping of nerve centres
(d) Mapping of the brain
Answer: (b) Mapping of genes
Explanation: Genome mapping determines where genes and molecular markers lie along chromosomes and estimates their order or physical distances. It supports research on inherited disorders, genetic linkage and plant or animal breeding. It is not a map of cerebral or nerve structures.
1. When one gene controls two or more different characters simultaneously, the phenomenon is called:
[UPSC Civil Services Preliminary Examination, 2002]
(a) Apomixis
(b) Pleiotropy
(c) Polyploidy
(d) Polyteny
Answer: (b) Pleiotropy
Explanation: Pleiotropy describes the influence of one gene on multiple phenotypic characteristics. A single mutated gene may therefore affect several tissues or biological functions. Polyploidy involves extra chromosome sets, while apomixis refers to seed production without fertilisation.