17 public questions tagged with this topic.
A frameshift mutation alters the reading frame, leading to incorrect amino acid sequences.
Ref: NCERT Class 12 Biology Chapter 5: Molecular Basis of Inheritance DNA Structure Double Helix and Packaging - Nucleosome
A nonsense mutation results in a premature stop codon, leading to incomplete protein synthesis.
Ref: NCERT Class 12 Biology Chapter 5: Molecular Basis of Inheritance DNA Structure Double Helix and Packaging - Nucleosome
Point mutations do not always cause frameshift mutations; they can be silent or missense mutations.
Ref: NCERT Class 12 Biology Chapter 4: Principles of Inheritance and Variation Sex Determination Mutation and Genetic Disorders
Silent mutations do not change the amino acid sequence, as the altered codon still codes for the same amino acid.
Ref: NCERT Class 12 Biology Chapter 4: Principles of Inheritance and Variation Polygenic Inheritance Pleiotropy and Quantitative Inheritance
Molecular evolution studies changes in DNA, RNA and proteins over time. Neutral theory by Kimura proposes most molecular substitutions are neutral and fixed by drift at rate equal to mutation rate, explaining molecular clock constancy where synonymous mutations accumulate steadily. Mitochondrial DNA maternally inherited and pseudogenes evolving faster due to lack of constraint provide markers for phylogeny. Purifying selection removes deleterious variants. Therefore Constant mutation rate illustrates principle of molecular evolution and neutral processes. This concept integrates genetics, ecology and molecular evidence, frequently tested in NEET, GATE and CSIR-NET, highlighting links between genotype, phenotype and
Ref: Nei & Kumar, Molecular Evolution, Clocks and Purifying Selection.
Molecular evolution studies changes in DNA, RNA and proteins over time. Neutral theory by Kimura proposes most molecular substitutions are neutral and fixed by drift at rate equal to mutation rate, explaining molecular clock constancy where synonymous mutations accumulate steadily. Mitochondrial DNA maternally inherited and pseudogenes evolving faster due to lack of constraint provide markers for phylogeny. Purifying selection removes deleterious variants. Therefore Neutral mutation rate illustrates principle of molecular evolution and neutral processes. This concept integrates genetics, ecology and molecular evidence, frequently tested in NEET, GATE and CSIR-NET, highlighting links between genotype, phenotype and
Ref: Li, Molecular Evolution, Neutral Theory and Molecular Clocks.
Linear pathway A to E ordered by observing which supplements rescue growth of mutant blocked between C and D, applying bypass logic. Upstream intermediates A and B require functional conversion through blocked enzyme so they fail to restore growth because defect remains. Downstream products D and E bypass defect directly supplying end product for protein synthesis. Some textbooks include immediate precursor C as rescuing if accumulation drives leaky activity but principle remains downstream rescue indicates block position. Counting rescued mutants per supplement allows sequential arrangement of metabolites reflecting enzyme order along chromosome.
Ref: Griffiths et al., Introduction to Genetic Analysis, 12th ed., Chapter 14: Determining Pathway Order by Supplementation Rescue
Auxotrophic mutants fail on minimal medium because structural gene encoding enzyme for specific anabolic step carries lesion abolishing catalytic activity. Without functional enzyme pathway halts, intracellular pool of needed amino acid or vitamin depletes and protein synthesis stops preventing colony formation. Wild-type prototroph synthesises metabolite endogenously whereas mutant requires supplementation bypassing block. Beadle and Tatum isolated such mutants to prove each gene controls one reaction, with auxotrophy revealing gene-controlled biochemical lesion rather than defects in DNA replication or cell division machinery itself.
Ref: Griffiths et al., Introduction to Genetic Analysis, 12th ed., Chapter 14: Auxotrophs Pathway Blocks Enzyme Loss
Mobilization of transposable elements impacts genome through multiple mechanisms: insertion into coding exons disrupts open reading frame causing gene inactivation and null alleles, insertion into introns or near enhancers modulates transcription by providing promoters, splice sites, or insulators altering expression patterns, and transposition intermediates create double-strand breaks that trigger illegitimate recombination leading to deletions, inversions, or translocations. Collectively these effects explain why host silencing via piRNAs, siRNAs, and heterochromatin repression is essential for maintaining stability while permitting evolutionary innovation. This principle illustrates essential molecular mechanisms governing replication fidelity and mutation fixation relevant for exam interpretation.
Ref: Watson et al., Molecular Biology of the Gene, 7th ed., Chapter 12: Functional Consequences of TE Mobilization
Most newly arising loss-of-function mutations are phenotypically recessive because diploid organisms possess two gene copies and many gene products are haplosufficient, meaning one functional allele produces sufficient protein for normal physiology. Complete loss from single allele is compensated by wild-type counterpart, so heterozygotes appear wild type and phenotype emerges only in homozygous mutants lacking functional product. This recessive behavior allows deleterious alleles to persist cryptically in carriers, explaining carrier frequencies in human genetics and complementation testing in model organisms. This principle illustrates essential molecular mechanisms governing replication fidelity and mutation fixation relevant for exam interpretation.
Ref: Alberts et al., Molecular Biology of the Cell, 7th ed., Chapter 8: Recessive Nature of Loss-of-Function Mutations
Restriction endonucleases recognize specific palindromic tetra- to octanucleotide sequences and introduce double-strand breaks at those sites. A single nucleotide polymorphism within recognition motif abolishes existing site or creates new site, altering fragment lengths after digestion, which appears as restriction fragment length polymorphism on gels. For example, sickle cell GAG to GTG mutation destroys MstII site. VNTR and STR polymorphisms involve tandem repeat copy number, not restriction recognition changes, while ESTs represent transcribed sequences. Therefore SNPs commonly provide molecular basis for RFLP variation and linkage studies.
Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.
Provide selective growth advantage, is consistent with established principles of cell signaling, receptor pharmacology and cellular regulation. Experimental measurements of binding parameters, genetic loss-of-function studies and pharmacological interventions all converge on the same interpretation. Related options address neighboring concepts but do not satisfy the precise criterion stated in the question.
Ref: NCERT Biology Class 11–12 Alberts et al Molecular Biology of the Cell Lodish et al, Molecular Cell Biology Cooper & Hausman, The Cell Abbas et al., Cellular and Molecular Immunology (for immunology sections)
