Heredity is part of Biology. Below are notes on 13 sub-topics, followed by practice MCQs from State PSC and UPSC papers.

Chromosomal Theory of Inheritance

  • Chromosomal Theory of Inheritance proposed by Walter Sutton & Theodor Boveri (1902-1903).
  • This theory states that chromosomes are the carriers of hereditary information.
  • Chromosome number is constant for a given species.
  • A gene is a functional segment of DNA.
  • The double-helical structure of DNA was proposed by James Watson & Francis Crick (1953).
  • James Watson, Francis Crick, and Maurice Wilkins were awarded the Nobel Prize in Physiology or Medicine in 1962 for their discoveries concerning the molecular structure of nucleic acids.
  • Humans possess 23 pairs of chromosomes (46 total).
  • In wheat, the Ph gene, which suppresses homologous pairing between chromosomes, is located on chromosome 5B.
  • Tor Khudree (Mahseer fish) has 2n=100 chromosomes.

Gene Interactions (Epistasis)

  • Epistasis: One gene (epistatic) masks or modifies the expression of another gene (hypostatic) at a different locus.
  • Complementary Gene Interaction (Duplicate Recessive Epistasis): F2 phenotypic ratio 9:7 (2 phenotypes).
  • Recessive Epistasis (Supplementary Gene Interaction): F2 phenotypic ratio 9:3:4 (3 phenotypes).
  • Dominant Epistasis: F2 phenotypic ratio 12:3:1 (3 phenotypes).
  • Inhibitory Gene Interaction (Dominant Inhibitory Epistasis): F2 phenotypic ratio 13:3 (2 phenotypes).
  • Duplicate Dominant Gene Interaction: F2 phenotypic ratio 15:1 (2 phenotypes).
  • Gene-for-gene hypothesis: Proposed by H.H. Flor (1956); describes interaction between host resistance gene and pathogen avirulence gene.

Human Genetic Disorders (Mendelian and Chromosomal)

  • Normal human somatic cells are diploid (2n) with 46 chromosomes.
  • Humans have 23 pairs of chromosomes: 22 pairs of autosomes and 1 pair of sex chromosomes (XX for females, XY for males).
  • Rh incompatibility is a genetic factor that can pose risks in biological marriage.
  • Rh incompatibility occurs when an Rh-negative mother carries an Rh-positive fetus.
  • In such cases, the mother's immune system can produce antibodies against the Rh-positive fetal blood cells, potentially causing Hemolytic Disease of the Newborn (HDN) in subsequent Rh-positive pregnancies.

Incomplete Dominance and Co-dominance

  • Incomplete Dominance:
    • Definition: Heterozygote (F₁) expresses an intermediate phenotype, a blend of parental traits.
    • Neither allele is completely dominant over the other.
    • F₂ phenotypic ratio is identical to F₂ genotypic ratio (1:2:1).
    • Example: Snapdragon (Antirrhinum majus) flower color (Red x White = Pink F₁).
    • Example: Mirabilis jalapa (Four o'clock plant) flower color.
  • Co-dominance:
    • Definition: Both alleles express themselves fully and simultaneously in the heterozygote.
    • No blending; both parental traits are distinctly expressed.
    • F₂ phenotypic ratio is identical to F₂ genotypic ratio (1:2:1).
    • Example: ABO blood group system in humans (alleles IA and IB are co-dominant).
    • Example: Roan coat color in cattle (both red and white hairs are present).

Linkage and Recombination

  • Linkage Group: A set of genes located on the same chromosome. The number of linkage groups in an organism is generally equal to its haploid number of chromosomes.
  • Grasshopper Linkage Groups: Female grasshopper (2n=24, XX) and Male grasshopper (2n=23, XO) both possess 12 linkage groups (11 autosomes + X chromosome).
  • Sex-linked inheritance: Established by T.H. Morgan using Drosophila melanogaster.
  • Bacterial Transduction & Conjugation: Discovered by Lederberg (with Zinder for transduction, and Tatum for conjugation).
  • DNA Polymerase isolation: Arthur Kornberg isolated DNA polymerase (DNA Pol I) from E. coli.
  • Genetic Code: H.G. Khorana made significant contributions to establishing the complete genetic code, including synthesizing DNA/ RNA segments.
  • Recombination Frequency: The frequency of recombination between two genes is directly proportional to the physical distance between them on a chromosome.
  • Factors decreasing Recombination Frequency:
    • Genes located very close to each other.
    • Chromosomal inversions: Suppress viable recombinant products by causing gamete inviability due to unbalanced chromosomes formed during crossing over within the inverted region in heterozygotes.

Mendel's Laws of Inheritance

  • Genetics is the study of patterns of inheritance and variation of characters from parents to offspring.
  • Inheritance is the process of transfer of characters from one to the next generation.
  • DNA (Deoxyribonucleic Acid) is responsible for controlling hereditary characters of living cells.
  • The DNA double helix structure was discovered by James Watson and Francis Crick.
  • Rosalind Franklin and Maurice Wilkins provided crucial X-ray diffraction images (e.g., "Photo 51") essential for the DNA structure discovery.
  • mRNA stands for Messenger Ribonucleic Acid.
  • Transcription is the process of copying genetic information from one strand of DNA into RNA.
  • Gregor Mendel is known as the "Father of Genetics."
  • Mendel first enunciated the principles of heredity and proposed the "Particulate theory of inheritance."
  • Mendel's experimental material was the Pea plant (Pisum sativum).
  • Alleles are different varieties of the same gene, or genes which code for a pair of contrasting traits.
  • In Mendel's monohybrid cross (e.g., pure tall plant crossed with a dwarf plant), all F₁ progeny were tall due to the principle of Dominance.
  • According to Mendel's Law of Independent Assortment, genes assort independently during gamete formation.
  • Hybridization is a process of crossing between genetically dissimilar plants (e.g., intervarietal, interspecific, intergeneric).
  • Intragenic crossing does not refer to hybridization.

Monohybrid and Dihybrid Crosses

  • Monohybrid Cross: Examines inheritance of a single pair of contrasting characters.
  • Monohybrid Cross F1 Gen: All offspring display the dominant phenotype, being heterozygous (e.g., TT x tt → Tt).
  • Monohybrid Cross F2 Gen (Phenotypic Ratio): 3 Dominant : 1 Recessive (e.g., 3 Tall : 1 Short).
  • Monohybrid Cross F2 Gen (Genotypic Ratio): 1 Homozygous Dominant : 2 Heterozygous : 1 Homozygous Recessive (e.g., 1 TT : 2 Tt : 1 tt).
  • In a monohybrid cross, the ratio of pure tall (TT) to short (tt) plants in the F₂ generation is 1:1.
  • Monohybrid crosses provide the basis for Mendel's Law of Segregation.
  • Dihybrid Cross: Examines inheritance of two pairs of contrasting characters simultaneously.
  • Dihybrid Cross F2 Gen (Phenotypic Ratio): 9:3:3:1 (e.g., 9 Round Yellow : 3 Round Green : 3 Wrinkled Yellow : 1 Wrinkled Green).
  • Mendel's Law of Independent Assortment is based upon observations from Dihybrid crosses.

Multiple Alleles and ABO Blood Groups

  • Multiple alleles: A gene having more than two alleles (variants) in a population.
  • ABO blood groups are a classic example of multiple alleles.
  • Three alleles control human ABO blood groups: IA, IB, and i.
  • Alleles IA and IB are co-dominant to each other.
  • Alleles IA and IB are both completely dominant over allele i.
  • Genotypes & Phenotypes:
    • Blood Group A: IAIA or IAi
    • Blood Group B: IBIB or IBi
    • Blood Group AB: IAIB (co-dominance)
    • Blood Group O: ii
  • Parental Crosses & Offspring Possibilities:
    • If one parent has blood group A and the other has blood group B, their biological child can have any of the four blood groups: A, B, O, or AB.
    • This occurs when both parents are heterozygous (e.g., IAi x IBi).
    • For parents with A and B blood groups to have a child with O blood group, both parents must be heterozygous (IAi and IBi).
    • If a man with blood group A marries a woman with blood group AB (IAIB):
      • If the man is heterozygous (IAi), the possible offspring blood groups are A, B, and AB.
      • The presence of a child with blood group B (IBi) specifically indicates that the man with blood group A must be heterozygous (IAi).
  • ABO blood group system was discovered by Karl Landsteiner in 1900.

Mutations: Types, Causes, and Significance

  • Genes are the basic units of heredity, made up of nucleic acids (DNA).
  • Deoxyribonucleic acid (DNA) is the short form of deoxyribonucleic acid.
  • The double helix model of DNA was proposed by Watson and Crick.
  • The structure of DNA, particularly the complementarity of its two strands, makes it uniquely suited to store and transmit genetic information.
  • The pentose sugar present in DNA is $\beta$D-2-deoxyribose.
  • DNA contains nitrogenous bases: Adenine (A), Guanine (G), Cytosine (C), and Thymine (T).
  • RNA contains nitrogenous bases: Adenine (A), Guanine (G), Cytosine (C), and Uracil (U). Uracil is found in RNA but not in DNA, replacing Thymine.
  • The genetic code is a triplet of nucleotide bases corresponding to 20 amino acids.
  • Characteristics of the genetic code include: it is universal, non-overlapping, non-ambiguous, commaless, and has start/stop codons.
  • A mutation is a change in the base sequence within a gene.
  • A mutagen is a physical or chemical agent capable of causing a mutation in the DNA of a cell.
  • Ultraviolet (UV) radiation is an example of a mutagen.
  • The Hardy-Weinberg principle explains the constant allele frequency in a population under specific conditions (absence of mutation, selection, genetic drift, gene flow, nonrandom mating).

Pedigree Analysis

  • Pedigree Analysis: Study of inheritance patterns of traits within families using standardized symbols across generations.
  • DNA Test (DNA Fingerprinting/Profiling): The definitive method for establishing biological parentage and genetic relationships.
  • Principle of DNA Test for parentage: Compares unique DNA segments (e.g., VNTRs, STRs) between a child and alleged parents. A child inherits half of its DNA markers from the biological mother and half from the biological father.
  • Applications of DNA testing: Confirming maternity/paternity, forensic identification, genetic disease diagnosis, lineage tracking.
  • Vidal Test: Diagnostic test for enteric fever (Typhoid).
  • Tuberculin Test: Screening test for Mycobacterium tuberculosis infection (Tuberculosis).
  • ELISA Test: Detects antibodies or antigens in a sample, used for diagnosing various infectious diseases (e.g., HIV, Hepatitis).

Polygenic Inheritance and Pleiotropy

  • Polygenic Inheritance: Multiple genes (polygenes) control a single phenotypic trait.
  • Each gene in polygenic inheritance contributes additively or cumulatively to the trait.
  • Polygenic traits typically exhibit continuous variation and a bell-shaped frequency distribution in a population (e.g., human skin color, human height).
  • Also known as Quantitative Inheritance.
  • Commercial edible wheat (Triticum aestivum) is a hexaploid organism with an ABD genome, a complex genetic background influencing many polygenic traits.
  • Pleiotropy: A single gene controls two or more different, seemingly unrelated, phenotypic characters simultaneously.
  • Pleiotropic effects often arise when the gene product is involved in multiple metabolic pathways or developmental processes.
  • Examples of pleiotropy:
    • Phenylketonuria (PKU): A single gene defect leads to mental retardation, reduced hair and skin pigmentation.
    • Sickle Cell Anemia: A single gene mutation in the beta-globin gene causes abnormal red blood cell shape, anemia, and increased resistance to malaria.
    • Starch synthesis in pea seeds: One gene influences both the size of starch grains and the shape of the seed (round vs. wrinkled).

Sex Determination and Sex-Linked Inheritance

  • In humans, sex determination is chromosomal. Females are homogametic (XX) and males are heterogametic (XY).
  • Human females produce only X-bearing ova. Human males produce X-bearing and Ybearing sperm.
  • The sex of the offspring in humans is determined by the father's sperm: X-sperm results in a female (XX), Y-sperm results in a male (XY).
  • A normal female child (XX) inherits one X chromosome from her mother and one X chromosome from her father.
  • If a human zygote inherits an X-chromosome from the father, it will develop into a girl (XX).
  • Sex-linked inheritance refers to traits governed by genes on the sex chromosomes, primarily the X chromosome.
  • X-linked recessive traits are more common in males as they are hemizygous for the X chromosome.
  • Colour blindness is an X-linked recessive disorder.
  • If a normal visioned man (XNY) and a normal visioned woman (XNXc, a carrier, whose father was colour-blind) marry, their daughters will always have normal vision (either XNXN or XNXc). The probability of a colourblind daughter (XcXc) is 0%.
  • If a colour-blind woman (XcXc) marries a normal visioned man (XNY), all their sons (XcY) will be colour-blind, and all their daughters (XNXc) will have normal vision but will be carriers.
  • In Drosophila, eye colour is an X-linked trait where red eye colour (XR) is dominant over white eye colour (Xr).
  • A cross between a white-eyed female Drosophila (XrXr) and a red-eyed male Drosophila (XRY) will produce F1 females (XRXr) that all have red eyes.

Test Cross and Back Cross

  • Test Cross:
  • Purpose: To determine the genotype (homozygous dominant or heterozygous) of an individual exhibiting a dominant phenotype.
  • Method: Crossing the individual with unknown genotype (e.g., T) with a homozygous recessive individual (e.g., tt).
  • Interpretation 1: If all progeny express the dominant trait, the unknown individual was homozygous dominant (e.g., TT x tt → all Tt).
  • Interpretation 2: If progeny show both dominant and recessive traits in a 1:1 ratio, the unknown individual was heterozygous (e.g., Tt x tt → 1 Tt : 1 tt).
  • Application: Essential for verifying pure lines, identifying hybrids, and determining the genetic makeup of an organism with a dominant trait (e.g., verifying if a tall plant is TT or Tt).
  • Back Cross:
  • Definition: Crossing a hybrid individual (e.g., F1 generation) with either of its parental genotypes.
  • Types: Can be with the dominant parent (e.g., F1 x P-dominant) or the recessive parent (e.g., F1 x P-recessive).
  • Relationship to Test Cross: A Test Cross is a specific type of Back Cross, where the hybrid is crossed with the homozygous recessive parent.
  • Purpose: Often used in breeding to introduce desirable traits from a donor parent into a recurrent parent's genetic background or to recover the genetic makeup of a recurrent parent.

6. Biofertilizers

Practice MCQs: Heredity

Chromosomal Theory of Inheritance

  1. Chromosome number in any species

    Asked in: CGPSC Prelims Exam 2019

    1. increase by age.
    2. decrease by age.
    3. is constant.
    4. increase with the weight.
    Show answer

    Answer: C. is constant.

    Except for the gametes (sex cells), which have half the number of chromosomes (haploid), the number of chromosomes in the somatic cells of individuals within a healthy species is characteristic and constant (diploid). For example, humans typically have 46 chromosomes (23 pairs).

  2. Chromosomal theory of inheritance was given by:

    Asked in: B. glycogen is made in animal cells, but starch is · UPSC CAPF 2023 · JPSC CS Prelims 2021

    1. Muller
    2. Waldeyer
    3. Mendel
    4. Sutton and Boveri
    Show answer

    Answer: D. Sutton and Boveri

    made in plant cells. C. both starch and glycogen are present in animal and plant cells. D. both starch and glycogen are present in plant cells only. Ans: B - Both starch and glycogen are glucose polymers used for energy storage. - Starch is found in plants. - Glycogen is found in animals and fungi. This theory was crucial in establishing genetics as a field and provided a physical basis for Mendel's abstract laws of inheritance. It proposed that chromosomes occur in pairs, homologous chromosomes separate during meiosis, and their behavior mirrors the segregation and independent assortment of genes described by Mendel.

  3. Who among the following shared the Nobel Prize in 1962 along with Francis Crick and James Watson for their discoveries concerning the molecular structure of nucleic acids ?

    Asked in: UPSC NDA 2 2017

    1. Erwin Chargaff
    2. Maurice Hugh Frederick Wilkins
    3. Rosalind Franklin
    4. Phoebus Levene
    Show answer

    Answer: B. Maurice Hugh Frederick Wilkins

    The discovery of the double helix structure of DNA by Watson, Crick, and Wilkins, significantly aided by the X-ray diffraction work of Rosalind Franklin (who was not awarded as the prize is not posthumous), was a landmark achievement in molecular biology.

  4. Double-helical structure of DNA was given by whom?

    Asked in: UPPCS Prelims 2018

    1. Jacob and Monod
    2. Watson and Crick
    3. H.G. Khorana
    4. None of the above
    Show answer

    Answer: B. Watson and Crick

    The double-helical structure of DNA explained how genetic information is stored and replicated, forming the cornerstone of molecular biology.

  5. In wheat, the Ph gene which suppresses homologous pairing between chromosomes is located on

    Asked in: Agri. Officer 2020

    1. 5B
    2. 5D
    3. 5A
    4. 5C
    Show answer

    Answer: A. 5B

    The Ph locus on the long arm of chromosome 5B is a major regulator of meiotic chromosome pairing in bread wheat (Triticum aestivum). In the presence of the Ph gene, homologous chromosomes are strongly attracted, leading to precise pairing. When this gene is absent (e.g., in nullisomic 5B), homologous chromosomes fail to pair properly, and instead, the more weakly homologous chromosomes (homeologous) pair, which can lead to aneuploidy and reduced fertility.

  6. Number of chromosomes in Tor Khudree are : - (5) Question not attempted

    Asked in: Asst. Fisheries Development Officer 2024

    1. (1) $2n=54$
    2. (2) $2n=118$
    3. (3) $2n=100$
    4. (4) $2n=50$
    Show answer

    Answer: A. (1) $2n=54$

    The diploid chromosome number ($2n$) for Tor Khudree is 54.

  7. How many pairs of chromosomes are present in humans ?

    Asked in: Clerk GR II Comb. Comp. Exam 2013

    1. 23
    2. 26
    3. 33
    4. 36
    Show answer

    Answer: A. 23

    The normal human karyotype consists of 46 chromosomes arranged in 23 pairs. This number is characteristic of the human species.

Gene Interactions (Epistasis)

  1. In which of the following, 3 different phenotypes are observed?

    Asked in: Agri. Officer 2020

    1. Duplicate gene interaction
    2. Complimentary gene interaction
    3. Supplementary gene interaction
    4. Inhibitory gene interaction
    Show answer

    Answer: C. Supplementary gene interaction

    - Duplicate gene interaction (recessive epistasis) Two genes, where recessive alleles at either locus mask the phenotype (e.g., 9:7 ratio). - Complementary gene interaction (dominant epistasis) Dominant allele at one locus masks the expression of alleles at another locus (e.g., 12:3:1 or 13:3 ratio). - Supplementary gene interaction (duplicate recessive epistasis) A dominant allele at one locus is required for expression of another gene, and the dominant allele at the second gene produces a different phenotype. This can lead to a 9:3:4 ratio in the F2 generation, showing three distinct phenotypes. - Inhibitory gene interaction (dominant suppression) Dominant allele at one locus suppresses the expression of another gene (e.g., 13:3 ratio).

  2. Gene for gene hypothesis was given by

    Asked in: Agri. Officer 2020

    1. H.H. Flor
    2. J.E. Vanderplank
    3. Hansen and Smith
    4. P.A. Michelli
    Show answer

    Answer: A. H.H. Flor

    Flor's gene-for-gene concept is a foundational principle in plant pathology and genetics, explaining the genetic basis of host-pathogen interactions and the evolution of disease resistance. J.E. Vanderplank contributed significantly to understanding disease resistance and epidemics, but Flor is credited with the gene-for-gene hypothesis.

Human Genetic Disorders (Mendelian and Chromosomal)

  1. Which of the following should be avoided in biological marriage ?

    Asked in: OPSC CS Prelims 2015

    1. A⁺ boy and A⁻ girl
    2. A⁺ boy and A⁺ girl
    3. O⁺ boy and O⁺ girl
    4. AB⁺ boy and AB⁺ girl
    Show answer

    Answer: A. A⁺ boy and A⁻ girl

    Rh incompatibility is a medical condition where the mother has Rh-negative blood (e.g., O⁻, A⁻, B⁻, AB⁻) and the baby has Rh-positive blood (inherited from the father). The mother's immune system can react to the baby's Rh-positive blood cells.

  2. Human genome has how many chromosomes?

    Asked in: lower devision clerk 2025

    1. 23
    2. 46
    3. 44
    4. 48
    Show answer

    Answer: B. 46

    Chromosomes are thread-like structures found in the nucleus of most living cells, carrying genetic information in the form of DNA. Humans inherit half of their chromosomes from each parent.

  3. The diploid number of chromosomes in human body

    Asked in: Forest Officer (RFO) 2018

    1. 12×2=24
    2. 20×2=40
    3. 23×2=46
    4. 24×2=48
    Show answer

    Answer: C. 23×2=46

    Human somatic cells are diploid, containing 46 chromosomes (23 pairs).

Incomplete Dominance and Co-dominance

  1. A pure red flower bearing plant is crossed with a pure white flower and the F₁ plant bears pink flowers. This is an example of

    Asked in: WBPSC CS Prelims 2016

    1. Pseudo dominance
    2. Dominance
    3. Epistasis
    4. Co-dominance
    Show answer

    Answer: B. Dominance

    The phenomenon described, where the F₁ generation exhibits an intermediate phenotype (pink) from parents with contrasting traits (red and white), is known as incomplete dominance. Neither allele is completely dominant over the other, resulting in a blend. However, 'Incomplete Dominance' is not an option. Among the given choices, 'Dominance' is the general term referring to the interaction between alleles where one influences the phenotype more than the other. While incomplete dominance is distinct from complete dominance, the term "Dominance" might be used here in a broader, albeit inaccurate, context to represent allelic interaction at a single locus, distinguishing it from phenomena like epistasis or co-dominance.

  2. Which among the following is an example of incomplete dominance ?

    Asked in: Clerk GR II Comb. Comp. Exam 2013

    1. Pea
    2. Papaya
    3. Snapdragon
    4. Tomoto
    Show answer

    Answer: C. Snapdragon

    Incomplete dominance occurs when neither allele in a heterozygous genotype is completely dominant over the other, resulting in a blended or intermediate phenotype.

Linkage and Recombination

  1. How many linkage groups are present in the female and male grasshopper insect?

    Asked in: MPSC CS Prelims 2019

    1. 04 and 04
    2. 10 and 10
    3. 12 and 12
    4. 23 and 24
    Show answer

    Answer: C. 12 and 12

    - Linkage groups represent sets of genes on the same chromosome that tend to be inherited together. - The number of linkage groups corresponds to the number of unique chromosomes in a haploid set.

  2. Match List I with List II and select the correct answer using the codes given below the Lists: List II List I (Scient‐ (Achievement in genetics) ists) I. Discovery of tramsdiction and A) Khur‐ Conjugation in bacteria ana II. Establishing the sex-linked in‐ B) Kornheritance berg III. Isolation of DNA polymerase C) Lederform E. coli berg D) Mor‐ IV. Establishing the complete gan genetic code E) Ochoa

    Asked in: UPPCS Prelims 2001

    1. I-D, II-C, III-B, IV-A
    2. I-C, II-D, III-A, IV-E
    3. I-D, II-C, III-A, IV-E
    4. I-C, II-D, III-B, IV-A
    Show answer

    Answer: D. I-C, II-D, III-B, IV-A

    - Joshua Lederberg significantly contributed to bacterial genetics, discovering bacterial conjugation with Edward Tatum and transduction with Norton Zinder. - Thomas Hunt Morgan's work on Drosophila established the principles of sex-linked inheritance and gene linkage. - Arthur Kornberg isolated DNA polymerase I, an enzyme essential for DNA replication, from E. coli. - Har Gobind Khorana was instrumental in cracking the genetic code, specifically by synthesizing polynucleotides of defined sequences which helped confirm codon assignments. Severo Ochoa also contributed to this effort.

  3. Which of these decrease the frequency of recombination between two genes?

    Asked in: Agri. Officer 2020

    1. Mitomycin C treatment
    2. Gamma irradiation
    3. Inversion
    4. Larger distance between those genes
    Show answer

    Answer: C. Inversion

    - Mitomycin C treatment & Gamma irradiation These are mutagens that can cause DNA damage and mutations. They generally increase the likelihood of recombination or chromosome aberrations, not decrease recombination between specific genes. - Larger distance between genes Genes that are far apart on a chromosome tend to recombine more frequently, not less. - Inversion A chromosomal rearrangement that, when heterozygous, can lead to reduced recombination in the inverted region. This is because crossing over within the inverted segment and subsequent chromosome breakage can lead to unbalanced gametes that are not viable. This selective disadvantage for recombinant chromosomes effectively suppresses recombination.

Mendel's Laws of Inheritance

  1. Which of the following is responsible for controlling hereditary characters of the living cells ?

    Asked in: BPSC Prelims Exam 60 62rd

    1. Enzyme
    2. Hormone
    3. RNA
    4. DNA
    Show answer

    Answer: D. DNA

    DNA contains the genetic instructions used in the development, functioning, growth, and reproduction of all known organisms and many viruses. Genes, which are segments of DNA, carry the code for specific proteins or functional RNA molecules. These proteins and RNA molecules determine the traits (hereditary characters) of an organism. While RNA, enzymes, and hormones are crucial molecules in cells, their production and function are ultimately directed by the information encoded in the DNA.

  2. Who discovered DNA?

    Asked in: BPSC Prelims Exam 64th

    1. James Watson and Francis Crick
    2. Gregor Mendel
    3. Johannsen
    4. Hargovind Khorana
    Show answer

    Answer: A. James Watson and Francis Crick

    - James Watson and Francis Crick proposed the double helix structure of DNA. - This structural discovery was key to understanding DNA's function as genetic material. - Other scientists like Mendel, Johannsen, and Khorana made significant contributions to genetics but are not credited with the discovery of the DNA structure itself.

  3. The DNA double helix structure was discovered by

    Asked in: BPSC Prelims Exam 69th

    1. James Watson and Francis Crick
    2. Rosalind Franklin and Maurice Wilkins
    3. Linus Pauling
    4. Gregor Mendel
    Show answer

    Answer: A. James Watson and Francis Crick

    - Watson and Crick built the final, correct structural model of DNA. - Their work was significantly informed by the experimental data, particularly X- ray crystallography, provided by Rosalind Franklin and Maurice Wilkins.

  4. What is the expanded form of the term ‘mRNA’ that has been widely discussed since the beginning of the pandemic?

    Asked in: BPSC Prelims Exam 69th

    1. Messenger Ribonucleic Acid
    2. Mutant Ribonucleic Acid
    3. Modified Ribonucleic Acid
    4. Mnemonic Ribonucleic Acid
    Show answer

    Answer: A. Messenger Ribonucleic Acid

    - mRNA stands for Messenger Ribonucleic Acid. - It acts as a messenger molecule in the cell, carrying instructions for protein synthesis. - mRNA technology became widely discussed in the context of certain COVID-19 vaccines.

  5. The process of copying genetic information from one strand of DNA into RNA is termed as

    Asked in: UPSC CDS 1 2017

    1. translation
    2. transcription
    3. replication
    4. mutation
    Show answer

    Answer: B. transcription

    Knowing the central dogma of molecular biology (DNA -> RNA -> Protein) and the processes involved (replication, transcription, translation) is essential.

  6. Photo 51 refers to an image of

    Asked in: UPSC CDS 1 2024

    1. a crater on the Moon
    2. DNA molecules
    3. the virus responsible for COVID-19
    4. the virus responsible for common cold
    Show answer

    Answer: B. DNA molecules

    Photo 51 was an X-ray diffraction pattern of DNA, obtained by Rosalind Franklin and Raymond Gosling in 1952 at King's College London. This image was crucial in determining the double helix structure of DNA by James Watson and Francis Crick.

  7. Match List-I with List-II: List-I List-II

    Asked in: HPPSC HPAS Prelims 2020

    1. Gregor 1. Role of earthworms in soil Mendel fertility
    2. Harold C. 2. University of Vienna Urey A. A–4, B–3, C–2, D–1 B. A–3, B–4, C–1, D–2
    3. A–1, B–2, C–3, D–4
    4. A–2, B–3, C–4, D–2
    Show answer

    Answer: D. A–2, B–3, C–4, D–2

    Based on the likely full question (assuming List-I included Charles Darwin and Alexander Fleming, and List-II included Discovery of Deuterium and Discovery of Penicillin): - Gregor Mendel: Known as the father of modern genetics. Studied and taught at the University of Vienna. Thus, A maps to 2 (University of Vienna). - Harold C. Urey: American physical chemist, Nobel laureate for discovering deuterium (heavy hydrogen). Thus, B maps to 4 (Discovery of Deuterium). - Charles Darwin: Famous for his theory of evolution. Also wrote a book on the role of earthworms in soil formation and fertility. Thus, C maps to 1 (Role of earthworms in soil fertility). - Alexander Fleming: Scottish physician and microbiologist, Nobel laureate for discovering penicillin. Thus, D maps to 3 (Discovery of Penicillin).

  8. Gregor Mendel is often referred to as the Father of Genetics, since he first enunciated the principles of heredity. His experimental material was

    Asked in: MPSC CS Prelims 2018

    1. Fruit fly
    2. Bread mould
    3. Pea plant
    4. Rhesus monkey
    Show answer

    Answer: C. Pea plant

    Gregor Mendel, the "Father of Genetics", conducted his foundational experiments on heredity using the garden pea plant (Pisum sativum). He chose pea plants due to their distinct traits, ease of cultivation, and ability to control pollination.

Monohybrid and Dihybrid Crosses

  1. In pea, a pure tall plant (TT) is crossed with a short plant (tt). What will be the ratio of pure tall plants to short plants in the F₂ generation ?

    Asked in: UPSC CDS 2 2021

    1. 1:1
    2. 1:3
    3. 3:1
    4. 2:1
    Show answer

    Answer: A. 1:1

    - Pure tall genotype is TT, short genotype is tt. - F1 generation from TT x tt is always Tt (heterozygous tall). - F2 generation from Tt x Tt has genotypes TT, Tt, tt in ratio 1:2:1. - Pure tall is TT, short is tt.

  2. Phenotypic ratio of Mendelian Dihybrid cross is

    Asked in: WBPSC CS Prelims 2015

    1. 9:3:3:1
    2. 1:1:1:1
    3. 3:4:3:1
    4. 1:2:1:1
    Show answer

    Answer: A. 9:3:3:1

    This 9:3:3:1 ratio is observed when genes for the two traits are located on different chromosomes or are sufficiently far apart on the same chromosome to assort independently.

  3. Mendel's law of independent assortment is based upon observations of

    Asked in: Clerk GR II Comb. Comp. Exam 2013

    1. Monohybrid crosses
    2. Dihybrid crosses
    3. Test crosses
    4. Back crosses
    Show answer

    Answer: B. Dihybrid crosses

    A dihybrid cross involves the study of inheritance of two contrasting characters at a time. This allows for the observation of how genes for different traits are inherited independently.

Multiple Alleles and ABO Blood Groups

  1. एक जोड़े (कपल्स) को संदेह है ͩक उनके नवजात ͧशशु की हॉǔस्पटल में अदला-बदली हुई है। इस ͪववाद को सुलझाने के ͧलए रक्त वगर्गीकरण चाहा गया है। पुरुष का रक्त समूह A है तथा औरत का रक्त समूह B है। उनके जैͪवक ͧशशु का रक्त समूह हो सकता है : i. या तो A या B ii. A या B या O या AB iii. A या B या AB iv. AB सही ͪवकल्प चुǓनए :

    Asked in: HAS Prelims 2021

    1. के विलि i
    2. के विलि ii
    3. के विलि iii
    4. के विलि iv
    Show answer

    Answer: B. के विलि ii

    - Blood groups are determined by alleles I^A, I^B, and i. I^A and I^B are codominant, and i is recessive. - Blood Group A corresponds to genotypes I^A I^A or I^A i. - Blood Group B corresponds to genotypes I^B I^B or I^B i. - Blood Group AB corresponds to genotype I^A I^B. - Blood Group O corresponds to genotype ii. - The father has blood group A, so his genotype is either I^A I^A or I^A i. - The mother has blood group B, so her genotype is either I^B I^B or I^B i. - To determine all possible offspring genotypes/phenotypes, we consider all combinations of parental genotypes: 1. Father I^A I^A x Mother I^B I^B: Offspring: I^A I^B (Blood Group AB). 2. Father I^A I^A x Mother I^B i: Offspring: I^A I^B (Blood Group AB), I^A i (Blood Group A). 3. Father I^A i x Mother I^B I^B: Offspring: I^A I^B (Blood Group AB), I^B i (Blood Group B). 4. Father I^A i x Mother I^B i: Offspring: I^A I^B (Blood Group AB), I^A i (Blood Group A), I^B i (Blood Group B), ii (Blood Group O). - Considering all possible pairings of parental genotypes (as the exact genotype is not specified, only the phenotype), the possible blood groups for the child are A, B, AB, and O.

  2. A couple suspects a mix up of their new born baby in the hospital. Blood typing is sought to resolve the dispute. The man has blood group A and the woman has blood group B. Their biological child can have blood group i. Either A or B ii. A or B or O iii. A or B or AB iv. only AB Choose the correct option :

    Asked in: HAS Prelims 2021

    1. i only
    2. ii only
    3. iii only
    4. iv only
    Show answer

    Answer: C. iii only

    Blood group A can have genotypes IAIA or IAi. Blood group B can have genotypes IBIB or IBi. When a parent with type A (IAIA or IAi) and a parent with type B (IBIB or IBi) have a child, the possible blood types of the offspring depend on the specific genotypes of the parents.

  3. Father and mother having A and B blood group respectively

    Asked in: UPSC CAPF 2011

    1. cannot give birth to child with AB blood group
    2. cannot give birth to child with O blood group
    3. can give birth to child with O blood group
    4. cannot give birth to twin child with B blood group
    Show answer

    Answer: C. can give birth to child with O blood group

    Blood group A can have genotypes I^A I^A or I^A i, and blood group B can have genotypes I^B I^B or I^B i. A child with blood group O has the genotype ii. This genotype can only be formed if both parents contribute an 'i' allele.

  4. A man of blood group-A marries a woman of blood group-AB, which type of progeny would indicate that man is heterozygous?

    Asked in: WBCS Main Paper 4 2019

    1. O
    2. B
    3. A
    4. AB
    Show answer

    Answer: B. B

    Blood group genotypes are determined by alleles Iᴬ, Iᴮ, and i. Blood group A can be genotype IᴬIᴬ or Iᴬi. Blood group AB is genotype IᴬIᴮ. Blood group B is IᴮIᴮ or Iᴮi. Blood group O is ii. A child with blood group B (Iᴮi or IᴮIᴮ) from this marriage can only get the Iᴮ allele from the mother (who is AB, IᴬIᴮ). Therefore, the child must inherit either an i or an Iᴮ allele from the father. Since the father has blood group A, he cannot have the Iᴮ allele. He must contribute the i allele. A man with blood group A can only have the i allele if his genotype is Iᴬi (heterozygous).

  5. Who discovered ABO system?

    Asked in: ECONOMIC INVESTIGATOR(EO) 2019

    1. Edward Jenner
    2. Alexander G. Bell
    3. Louis Pasteur
    4. None of them
    Show answer

    Answer: D. None of them

    Karl Landsteiner's discovery of the ABO blood group system revolutionized blood transfusions, making them much safer by allowing for blood typing and matching.

Mutations: Types, Causes, and Significance

  1. Genes are made-up of

    Asked in: CGPSC Prelims Exam 2012

    1. nucleic acids
    2. proteins
    3. carbohydrates
    4. lipids
    Show answer

    Answer: A. nucleic acids

    Genes are composed of nucleic acids, primarily DNA.

  2. The characteristics features of genetic code are i. It is always universal ii. It is triplet of nucleotides bases corresponding to 20 amino acids iii. It is non-overlapping, non-ambiguous and commaless iv. It has start and stop codon Which of the statements given above are true ?

    Asked in: MPPSC CS Prelims 2020

    1. i, ii and iv only
    2. i, iii and iv only
    3. i, ii and iii only
    4. All of the above
    Show answer

    Answer: D. All of the above

    The genetic code is the set of rules by which information encoded within genetic material (DNA or RNA sequences) is translated into proteins (amino acid sequences) by living cells.

  3. Change in the base sequence within a gene is called :

    Asked in: OPSC CS Prelims 2020 · UPPCS Prelims 2020

    1. Mutation
    2. Cloning
    3. Fusion
    4. Breeding
    Show answer

    Answer: A. Mutation

    - Mutations can occur spontaneously or be induced by external factors (mutagens). - Mutations can lead to changes in the protein encoded by the gene, potentially affecting function.

  4. Who had proposed for the first time the double helix model of DNA ?

    Asked in: UPPCS Prelims 2012

    1. Watson and Crick
    2. Fisher and Haldoni
    3. Lamurk and Darwin
    4. HugodeVries
    Show answer

    Answer: A. Watson and Crick

    James Watson and Francis Crick are credited with proposing the double helix model of DNA structure in 1953. Their work was based on experimental data from other scientists, notably the X-ray diffraction images produced by Rosalind Franklin and Maurice Wilkins.

  5. Change in the base sequence within the gene is called

    Asked in: UPPCS Prelims 2016

    1. Breeding
    2. Cloning
    3. Mutation
    4. Fusion
    Show answer

    Answer: C. Mutation

    Mutation is a change in the DNA sequence of a gene.

  6. James D. Watson and Francis Crick are associated with the discovery of:

    Asked in: UPPSC Upper Mains 2012

    1. Vaccine
    2. Structure of DNA
    3. Anti-malerial drugs
    4. Penicilline
    Show answer

    Answer: B. Structure of DNA

    In 1953, James Watson and Francis Crick published a groundbreaking paper describing the double helix structure of deoxyribonucleic acid (DNA), the molecule that carries genetic information. Their work was based on X-ray diffraction data collected by Rosalind Franklin and Maurice Wilkins, as well as chemical information available at the time.

  7. Which of the following features of DNA makes in uniquely suited to store and transmit genetic information from generation to generation?

    Asked in: UPPCS Prelims 2001

    1. Complementarity of the two stands
    2. Double helix
    3. Number of base pairs per turn
    4. Sugar phosphate backbone
    Show answer

    Answer: A. Complementarity of the two stands

    The complementary base pairing (A-T, C-G) between the two DNA strands is fundamental for accurate DNA replication and transmission of genetic information.

  8. The short form of deoxyribonucleic acid is

    Asked in: District Library and Information Officer(DLIO) 2018

    1. DNA
    2. DDA
    3. DRA
    4. None of the above
    Show answer

    Answer: A. DNA

    Understanding scientific acronyms and their full forms is common in general knowledge and science sections of competitive exams.

Pedigree Analysis

  1. Two women put claim over a child as mother; which test can prove this claim to be true ?

    Asked in: Assistant Accountant 2012

    1. Vidal Test
    2. Tuberculin Test
    3. D.N.A. Test
    4. ELISA Test
    Show answer

    Answer: C. D.N.A. Test

    A D.N.A. Test is the most reliable method to determine biological parentage.

Polygenic Inheritance and Pleiotropy

  1. Human insulin molecule is composed of one α-chain having 21 amino acids and one β-chain having 30 amino acids. How many functional insulin genes occur in adult humans?

    Asked in: UPSC CDS 2 2017

    1. One
    2. Two
    3. Three
    4. Four
    Show answer

    Answer: A. One

    The gene encoding human insulin, INS, is located on chromosome 11. Humans are diploid organisms, meaning they have two sets of chromosomes (except for sex chromosomes in males). Therefore, a healthy individual has two copies of the INS gene, one on each of the homologous chromosome 11 pair. Both copies are typically functional, encoding the proinsulin precursor that is cleaved to form mature insulin.

  2. Which of the following genomic conditions is found in commercial edible wheat?

    Asked in: JPSC CS Prelims 2024

    1. AB genome
    2. ABC genome
    3. ABCD genome
    4. ABD genome
    Show answer

    Answer: D. ABD genome

    Commercial bread wheat (Triticum aestivum) is an allohexaploid (6x) with the genomic constitution AABBDD. This means it contains complete sets of chromosomes from three different ancestral diploid genomes, denoted as A, B, and D.

  3. When one gene control two or more different characters simultaneously, the phenomenon is called

    Asked in: UPPCS Prelims 2002

    1. Apomixis
    2. Pleiotropy
    3. Polyploidy
    4. Polytony
    Show answer

    Answer: B. Pleiotropy

    Pleiotropy occurs when a single gene influences multiple, seemingly unrelated phenotypic traits.

Sex Determination and Sex-Linked Inheritance

  1. In human beings, the chromosomes that determine birth of a normal female child are

    Asked in: UPSC CDS 2 2020

    1. one X chromosome from mother and one X chromosome from father
    2. one X chromosome from mother and one Y chromosome from father
    3. two X chromosomes from mother and one X chromosome from father
    4. one X chromosome and one Y chromosome from father and one X chromosome from mother
    Show answer

    Answer: A. one X chromosome from mother and one X chromosome from father

    The mother's gametes (ova) always carry an X chromosome. The father's gametes (sperm) carry either an X or a Y chromosome. Fertilization with an X- carrying sperm results in an XX zygote (female), while fertilization with a Y-carrying sperm results in an XY zygote (male).

  2. A husband and wife have normal vision but father of both of them were colour-blind. Probability of their first daughter to be colour-blind is

    Asked in: KPSC KAS Prelims 2014

    1. 25%
    2. 50%
    3. 75%
    4. 0%
    Show answer

    Answer: D. 0%

    - Colour blindness is typically an X-linked recessive trait. - Males transmit their X chromosome to their daughters and their Y chromosome to their sons. - Females transmit one of their two X chromosomes to both daughters and sons. - A daughter gets one X from the father and one X from the mother.

  3. What will be the eye colour of all female individuals in F1 generation when a white eyed female Drosophila is crossed with a red eyed male Drosophila ?

    Asked in: MPSC CS Prelims 2022

    1. White
    2. Red
    3. Mixture of Red & White
    4. Mixture of Red & Blue
    Show answer

    Answer: B. Red

    This is a classic example of X-linked dominant/ recessive inheritance. Females have two X chromosomes, while males have one X and one Y. Traits on the X chromosome are inherited differently in males and females.

  4. If a colour blind woman marries a normal visioned man, they will produce

    Asked in: TNPSC CS Prelims 2015

    1. Normal visioned sons and daughters
    2. Colour blind sons and normal visioned daugh‐ ters
    3. Normal sons and colour blind daughters
    4. Colour blind sons and daughters
    Show answer

    Answer: B. Colour blind sons and normal visioned daugh‐ ters

    Colour blindness is an X-linked recessive trait. A colour blind woman has the genotype X^c X^c (where X^c is the allele for colour blindness). A normal visioned man has the genotype X^C Y (where X^C is the allele for normal vision). When they have offspring, sons inherit an X chromosome from their mother and a Y chromosome from their father. All sons will inherit the X^c allele from their mother, resulting in the genotype X^c Y, which makes them colour blind. Daughters inherit one X chromosome from their mother and one X chromosome from their father. They will inherit X^c from the mother and X^C from the father, resulting in the genotype X^C X^c. Since normal vision (X^C) is dominant over colour blindness (X^c), all daughters will have normal vision but will be carriers of the colour blindness allele.

  5. Assertion (A): In human beings, the females play a maj ‘X’ chromosomes.

    Asked in: UPPCS Prelims 2000

    1. Both A and R are true, and R is the correct explanation of A
    2. Both A and R are true, but R is not a correct explanation of A
    3. A is true, but R is false
    4. A is false, but R is true
    Show answer

    Answer: D. A is false, but R is true

    Assertion (A) states that females play a major role in determining the sex of the offspring. This is false in human beings. Males have sex chromosomes XY, and females have XX. During gamete formation, females produce ova containing only X chromosomes, while males produce sperm containing either an X or a Y chromosome. The sex of the offspring is determined by the type of sperm that fertilizes the ovum: if an X sperm fertilizes, the offspring is XX (female); if a Y sperm fertilizes, the offspring is XY (male). Thus, the male gamete (sperm) determines the sex. Reason (R) states that women have two ‘X’ chromosomes. This is true for typical human females (XX).

  6. In humans a zygote which has an X-chromosome inherited from the father will develop into a :

    Asked in: Clerk GR II Comb. Comp. Exam 2013

    1. Boy
    2. Girl
    3. X-chromosome does not determine the sex of a child
    4. Either boy or girl
    Show answer

    Answer: B. Girl

    The sex of a human child is determined by the father's sperm. An X chromosome from the father results in a girl (XX), and a Y chromosome results in a boy (XY).

  7. A normal baby girl receives her X chromosomes from -

    Asked in: School Lecturer (School Edu.) 2018 3 2018

    1. her father only
    2. her mother only
    3. her mother and father both
    4. either her mother or father
    Show answer

    Answer: C. her mother and father both

    Sex determination in humans is based on the contribution of sex chromosomes from both parents. The mother always contributes an X chromosome, while the father can contribute either an X (resulting in a daughter) or a Y (resulting in a son).