🔬 Biology · Class 12 · NEET
Principles of Inheritance and Variation - Practice Questions with Answers 75 free MCQs on Principles of Inheritance and Variation, each with its own worked answer and explanation. Mendel's laws, inheritance patterns, DNA structure, and molecular biology. Core of NEET biology.
Take the timed Principles of Inheritance and Variation chapterwise test → 75 practice questions on Principles of Inheritance and Variation , sorted Easy → Hard. Try each one first, then open its answer page for the worked explanation. Want the full theory first? Read the Principles of Inheritance and Variation notes .
Monohybrid Cross: Tt x Tt Parent 1 (Tt) Parent 2 (Tt) gametes: T, t (from each parent) T t T t TT Tt Tt tt Ratio 1 TT : 2 Tt : 1 tt (3 tall : 1 short if T = tall is dominant) Punnett square for a monohybrid cross between two heterozygous (Tt) parents, showing the 3:1 phenotypic ratio predicted by Mendel's Law of Segregation.
Easy - 25 questions Q1.
Mendel carried out his classic hybridisation experiments on which plant?
A Garden pea (Pisum sativum)B Snapdragon (Antirrhinum majus)C Maize plant (Zea mays)D Sweet pea (Lathyrus odoratus)Show answer & explanation →
Q2.
Down syndrome is caused by an extra copy of chromosome number:
A number 18B number 21C number 13D number 23Show answer & explanation →
Q3.
The phenotypic ratio seen in the F<sub>2</sub> generation of a dihybrid cross is:
A 3:1B 1:2:1C 9:3:3:1D 1:1:1:1Show answer & explanation →
Q4.
Red-green colour blindness in humans is inherited as a trait that is:
A autosomal dominantB Y-linked dominantC X-linked dominantD X-linked recessiveShow answer & explanation →
Q5.
How many pairs of contrasting traits did Mendel select in the pea plant?
A Seven pairsB Five pairsC Four pairsD Nine pairsShow answer & explanation →
Q6.
DNA stands for:
A Di-nitrogen acidB Deoxyribonucleic acidC Deoxyribose nucleotide acidD Directed nucleic acidShow answer & explanation →
Q10.
A cross between a homozygous dominant (AA) and homozygous recessive (aa) gives:
A All AAB All AaC 25% AA : 50% Aa : 25% aaD 50% AA : 50% aaShow answer & explanation →
Q11.
In a monohybrid cross between two Aa parents, ratio of phenotypes in F<sub>2</sub>:
A 3:1 dominant:recessiveB 1:2:1 ratio as seen in incomplete dominanceC 1:1 ratio as seen in a test crossD All offspring showing the dominant phenotypeShow answer & explanation →
Q12.
The central dogma of molecular biology is:
A Protein → RNA → DNAB DNA → RNA → ProteinC RNA → DNA → ProteinD Protein → DNA → RNAShow answer & explanation →
Q13.
mRNA carries genetic information from:
A Ribosome to DNAB DNA (nucleus) to ribosomeC Ribosome to cytoplasmD tRNA to DNAShow answer & explanation →
Q14.
Haemophilia is an example of:
A Autosomal dominant traitB Autosomal recessive traitC X-linked recessive traitD Y-linked traitShow answer & explanation →
Q17.
RNA differs from DNA in having:
A Thymine instead of uracil, like DNAB Deoxyribose instead of ribose as its sugarC Uracil instead of thymine; ribose sugarD A stable double-stranded helical structureShow answer & explanation →
Q18.
Sickle cell anaemia is caused by:
A Large-scale deletion spanning the entire beta-globin gene clusterB Single base mutation in haemoglobin gene (point mutation)C Retroviral insertion disrupting globin gene expressionD Complete loss of chromosome 11 in red cell precursorsShow answer & explanation →
Q20.
ABO blood groups are an example of:
A Complete dominance of a single allele over all othersB Incomplete dominance producing a blended intermediate phenotypeC Co-dominance (A and B) with recessive OD Sex linkage carried on the X chromosomeShow answer & explanation →
Q21.
The structure of DNA was described by:
A Mendel and MorganB Watson and Crick (1953)C Avery, MacLeod, McCartyD Hershey and ChaseShow answer & explanation →
Q22.
A mutation in a body cell (somatic mutation) can cause:
A Heritable changes passed to all offspringB Cancer, but cannot be passed to offspringC Genetic disease appearing directly in offspringD Errors arising specifically during meiosisShow answer & explanation →
Q23.
Chromosomes are made of:
A RNA mainly, transcribed directly from the nucleolusB Protein mainly, folded into a fibrous keratin-like scaffoldC DNA and proteins (mainly histones)D Lipids and DNA bound by a phospholipid bilayerShow answer & explanation →
Q24.
Transcription is the process of making:
A DNA from RNA (reverse)B mRNA from a DNA templateC Protein from mRNAD DNA from proteinShow answer & explanation →
Q25.
Codon is:
A Three bases on tRNA that recognize the anticodonB Three bases on mRNA that code for one amino acidC One base on mRNA marking the start of translationD A sequence on DNA recognized by RNA polymeraseShow answer & explanation →
Medium - 25 questions Q26.
Mendel's law of segregation is also known as the law of:
A independent assortmentB purity of gametesC partial dominanceD complete linkageShow answer & explanation →
Q27.
The chromosomal constitution of an individual with Turner's syndrome is:
A 44 autosomes + XXYB 44 autosomes + XYYC 44 autosomes + XOD 44 autosomes + XXXShow answer & explanation →
Q28.
In honeybees, the male drones develop from unfertilised eggs by the process of:
A normal fertilisationB vegetative buddingC simple binary fissionD parthenogenesisShow answer & explanation →
Q29.
The phenomenon of linkage between genes was first discovered by:
A T. H. MorganB Gregor MendelC Walter SuttonD Hugo de VriesShow answer & explanation →
Q30.
Phenylketonuria is caused by the lack of an enzyme that converts:
A tyrosine into melanin pigmentB phenylalanine into tyrosineC glucose into glycogenD galactose into glucoseShow answer & explanation →
Q31.
In incomplete dominance, F<sub>1</sub> of RR x WW red and white snapdragons is:
A All red, like the dominant red parentB All white, like the recessive white parentC Pink (intermediate phenotype)D Half red, half white in a mosaic patternShow answer & explanation →
Q32.
The law of independent assortment states that:
A Alleles of the same gene fail to separate during meiosisB Genes on different chromosomes sort independently into gametesC All linked genes are always inherited together as one unitD Dominant alleles permanently mask recessive ones in offspringShow answer & explanation →
Q33.
Which scientist used X-ray crystallography data to help discover DNA structure?
A Linus PaulingB Rosalind FranklinC Erwin ChargaffD Frederick GriffithShow answer & explanation →
Q34.
Chargaff's rules state that in DNA:
A A = G and C = T, an unrelated pairing ruleB A = T and G = C (complementary base pairing)C A is generally found in greater amount than TD The ratio of A+T to G+C is generally constant within a speciesShow answer & explanation →
Q35.
Point mutation that changes one amino acid to another is called:
A Silent mutationB Frameshift mutationC Missense mutationD Nonsense mutationShow answer & explanation →
Q36.
Okazaki fragments are produced during:
A TranscriptionB Lagging strand DNA synthesisC Leading strand synthesisD Meiosis onlyShow answer & explanation →
Q37.
A test cross involves crossing an individual with unknown genotype with:
A Another individual of equally unknown genotypeB A known homozygous dominant individualC A known homozygous recessive (aabb...)D Another F<sub>1</sub> hybrid from the same crossShow answer & explanation →
Q38.
Sex-limited traits appear:
A Only in females, carried on the X chromosomeB Only in males, carried on the Y chromosomeC In both sexes but only fully expressed in one sexD Only in genes located on the X chromosomeShow answer & explanation →
Q39.
Genetic mapping uses recombination frequencies to:
A Determine the total chromosome number of an organismB Estimate relative distances between genes on a chromosomeC Locate point mutations directly within a geneD Determine the nucleotide sequence of a DNA strandShow answer & explanation →
Q40.
The Hershey-Chase experiment proved that:
A DNA has a double helix structure overallB DNA, not protein, is the genetic materialC Chromosomes are the carriers of hereditary genesD Enzymes are proteins that catalyze reactionsShow answer & explanation →
Q41.
Epigenetics refers to:
A Permanent, irreversible changes occurring within the underlying DNA nucleotide sequence itselfB Heritable changes in gene expression without DNA sequence change (e.g., methylation, acetylation)C Random point mutations that arise spontaneously during ordinary DNA replicationD Environmental effects that mainly influence seedling growth rate in young plantsShow answer & explanation →
Q42.
Repetitive DNA sequences that can move within the genome are called:
A Introns removed during pre-mRNA splicingB Transposons (jumping genes)C Exons retained in the mature mRNA transcriptD Promoters that recruit RNA polymerase to a geneShow answer & explanation →
Q43.
In which condition does a female carrier transmit a disease to half of her sons?
A Autosomal recessiveB X-linked dominantC X-linked recessiveD Y-linkedShow answer & explanation →
Q44.
RNA polymerase reads the template strand in which direction?
A 5' to 3', the same direction as mRNA synthesisB 3' to 5' (template read), synthesizing mRNA 5' to 3'C In one fixed direction that never varies across speciesD Bidirectionally, reading both strands simultaneouslyShow answer & explanation →
Q45.
Post-transcriptional modification of pre-mRNA includes:
A Mainly the enzymatic addition of a 5 prime methylguanosine cap structureB Capping (5 prime), poly-A tail (3 prime), and splicing out intronsC Mainly the removal of introns from the transcript by the spliceosome complexD Mainly the chemical methylation of cytosine bases within the DNA templateShow answer & explanation →
Q46.
The mutation that causes cystic fibrosis is most commonly:
A A point mutation creating a premature stop codon early in the CFTR transcriptB Deletion of 3 nucleotides in CFTR gene (phenylalanine deleted at position 508)C Duplication of an entire arm of chromosome 7 during meiosisD Insertion of an extra nucleotide causing a frameshift in the reading frameShow answer & explanation →
Q47.
Which enzyme unwinds the DNA double helix during replication?
A DNA polymeraseB PrimaseC HelicaseD LigaseShow answer & explanation →
Q48.
Lac operon in E. coli is an example of:
A Positive regulation mainly, requiring little repressor protein activityB Negative regulation (lac repressor) with positive control (CAP-cAMP)C Constitutive expression occurring regardless of lactoseD Eukaryotic gene regulation involving chromatin remodelingShow answer & explanation →
Q49.
Klinefelter syndrome (47,XXY) results in:
A Female with an extra X chromosome and tall statureB Male with extra X: infertile, some female featuresC Normal male with standard XY karyotypeD Turner syndrome arising from a missing X chromosomeShow answer & explanation →
Q50.
Genetic drift has the greatest effect in:
A Large, stable populationsB Small isolated populationsC Populations with high gene flowD Outcrossing populationsShow answer & explanation →
Hard - 25 questions Q51.
Pleiotropy is best described as a situation in which:
A two genes together control one single traitB many genes add up to control one traitC a single gene affects several traitsD the environment alone controls the traitShow answer & explanation →
Q52.
The chromosomal theory of inheritance was proposed by:
A Morgan and SturtevantB Watson and Crick togetherC Beadle and Tatum jointlyD Sutton and BoveriShow answer & explanation →
Q53.
Human skin colour, governed by several genes, is an example of:
A polygenic inheritanceB incomplete dominanceC multiple allelismD pleiotropic controlShow answer & explanation →
Q54.
Sturtevant used the frequency of recombination between linked genes to:
A determine the charge on the DNAB prepare genetic maps of chromosomesC count the number of chromosomesD measure the overall mutation rateShow answer & explanation →
Q55.
Thalassemia differs from sickle-cell anaemia mainly because thalassemia is a:
A structural defect of the globin chainsB problem of oxygen transport onlyC quantitative defect in globin synthesisD defect limited to the red cell membraneShow answer & explanation →
Q56.
Imprinting in genetics refers to:
A The random chemical marking of DNA bases for methylation occurring during cell replication according to conventional understandingB Parent-of-origin-specific gene expression (some genes expressed only from maternal or paternal allele)C The random inactivation of one X chromosome occurring within female somatic cells in routine practiceD The silencing of transposable genomic elements carried out by small interfering RNA molecules overallShow answer & explanation →
Q57.
Prader-Willi syndrome is caused by:
A Trisomy of chromosome 15 arising from meiotic nondisjunctionB Deletion of paternal chromosome 15q11-q13 (or maternal UPD15)C Deletion of the equivalent maternal region on chromosome 15D Presence of an extra X chromosome in a male karyotypeShow answer & explanation →
Q58.
The locus control region (LCR) regulates:
A Mainly the localized pattern of DNA methylation occurring across a single gene clusterB Long-range transcriptional regulation of gene clusters (e.g., globin gene cluster)C Mainly the removal of introns from pre-mRNA carried out by the spliceosome complexD Mainly the recruitment of ribosomes needed to begin translation of a mature mRNAShow answer & explanation →
Q59.
ENCODE project revealed that the human genome is:
A Composed mainly of protein-coding exons with relatively few introns presentB Made up of roughly 98% inert, largely non-functional junk DNA sequencesC Largely transcribed with most non-coding regions having biochemical functionD Composed mainly of transposons that serve little discernible biochemical functionShow answer & explanation →
Q60.
Alternative splicing allows one gene to produce:
A Exactly one single, fixed protein product with little variation across different tissuesB Multiple different proteins from the same pre-mRNA by including/excluding different exonsC Mainly two fixed protein variants regardless of the tissue type being examinedD Mainly progressively shorter, truncated protein products lacking key functional domainsShow answer & explanation →
Q61.
The SOS response in E. coli is triggered by:
A Prolonged nutrient starvation activating the stringent responseB DNA damage (RecA coprotease activity)C Exposure to high temperature alone, triggering heat-shock proteinsD Osmotic stress activating compatible solute accumulation pathwaysShow answer & explanation →
Q62.
Heterochromatin position effect (position effect variegation) occurs when:
A A gene is overexpressed due to amplification of its nearby promoter region in most cases under typical conditionsB A gene is moved near heterochromatin and silenced in some cells but not others (mosaic phenotype)C Every gene across the entire genome becomes uniformly silenced all at once according to standard textbooksD Chromosome inversion mainly disrupts ribosomal RNA gene clusters specifically in general practiceShow answer & explanation →
Q63.
Uniparental disomy (UPD) means:
A One copy of a chromosome inherited from each parent, as normalB Both copies of a chromosome pair from the same parentC An entire extra set of chromosomes added to the genomeD Random, unselective loss of a chromosome during cell divisionShow answer & explanation →
Q64.
The chi-square test in genetics is used to:
A Determine the precise nucleotide sequence of a geneB Test whether observed phenotype ratios fit expected Mendelian ratiosC Directly measure the recombination frequency between two lociD Determine the nucleotide sequence of an RNA transcriptShow answer & explanation →
Q65.
Trinucleotide repeat expansion diseases include:
A Sickle cell anemia and cystic fibrosis, both caused by simple point mutations as frequently describedB Huntington disease, myotonic dystrophy, fragile X syndrome (repeat tracts expand each generation)C Down syndrome and Turner syndrome, both caused by chromosome number changes overall in most textbook accountsD Mainly conditions following a generally autosomal recessive inheritance pattern during normal conditionsShow answer & explanation →
Q66.
X-inactivation in female mammals is:
A Largely permanent silencing of both X chromosomes occurring within most cell as generally observedB Random inactivation of one X in each somatic cell (forming Barr body), creating cellular mosaicismC Consistent inactivation of mainly the maternally inherited X chromosome each time in typical laboratory settingsD Inactivation of both X chromosomes occurring specifically within male individuals under usual circumstancesShow answer & explanation →
Q67.
XIST RNA is involved in:
A Coding directly for a protein enzyme that catalyzes the replication of DNAB Coating the inactive X chromosome and recruiting silencing factors (X-inactivation)C Repairing double-strand breaks within damaged genomic DNA exclusively, with no other roleD Directing and catalyzing the translation of mRNA transcripts at the ribosomeShow answer & explanation →
Q68.
Anticipation in genetic diseases is caused by:
A Improved diagnostic technology that detects disease earlier in a person's life according to most researchersB Trinucleotide repeat expansion through generations causing more severe disease at earlier onsetC Switching of parental imprinting marks occurring between successive generations in the majority of cases studiedD Translocation of a chromosome segment onto an unrelated non-homologous chromosome as widely reportedShow answer & explanation →
Q69.
In population genetics, the Hardy-Weinberg equilibrium requires:
A Active and ongoing natural selection acting consistently across the whole populationB No selection, no mutation, no migration, random mating, large population size (all 5 conditions)C A consistently small population size combined with frequent random genetic driftD Sustained, deliberate inbreeding occurring among closely related individuals in the populationShow answer & explanation →
Q70.
Quantitative trait loci (QTL) analysis identifies:
A Single-gene traits that generally follow simple Mendelian dominant-recessive inheritance patternsB Chromosomal regions containing multiple genes that together contribute to complex quantitative traitsC Mainly the dominant alleles that happen to be present at a given genetic locusD Mainly environmental factors that have no underlying genetic basis whatsoeverShow answer & explanation →
Q71.
The selfish DNA theory proposes:
A All DNA sequences present in the genome are sometimes thought to provide a direct, measurable fitness benefit to the organismB Repetitive and transposable DNA elements persist because they replicate themselves, not because they benefit the hostC Mainly protein-coding regions of the genome are sometimes thought to carry out any meaningful biochemical or regulatory functionD Non-coding junk DNA sequences are sometimes thought to be steadily eliminated from the genome over a long span of evolutionary timeShow answer & explanation →
Q72.
Epistasis occurs when:
A Two alleles of the exact same gene happen to interactB One gene masks or modifies the expression of another geneC All genes in the genome act largely independently of each otherD Genes located on the same chromosome generally do not interactShow answer & explanation →
Q73.
The founder effect is:
A Loss of alleles when a small group colonizes a new area (low genetic diversity from few founders)B Natural selection acting consistently across very large, stable population groups over timeC Gene flow occurring freely and continuously between two well-mixed populations nearbyD Sustained inbreeding occurring gradually within long-established, large populationsShow answer & explanation →
Q74.
CpG islands in the genome are:
A Genomic repetitive sequences that occur scattered randomly throughout most intronic regions of the genome in standard practiceB Regions with high C-G dinucleotide frequency, usually unmethylated near gene promoters; hypermethylation silences genes in cancerC Sequences found mainly packed within densely compacted, transcriptionally silent heterochromatin regions under most conditions encounteredD Regions of the genome characterized by an unusually elevated rate of meiotic recombination events as frequently observed in practiceShow answer & explanation →
Q75.
Two-hit hypothesis (Knudson) for tumor suppressors means:
A A single mutation occurring in just one allele of any gene is largely sufficient on its own to cause cancerB Both alleles of a tumor suppressor gene must be inactivated for cancer to occur (first hit germline, second somatic in familial cases)C Tumor formation usually and mainly requires the sequential activation of exactly two separate, unrelated oncogenes in the same cellD Invading viral particles must physically and mechanically strike the DNA double helix exactly twice during a single infection cycleShow answer & explanation →