Botany 2022 Paper II 50 marks Discuss

Q4

(a) How male sterility helps in heterosis breeding ? Discuss the application of barnase-barstar system in achieving heterosis. (10+10=20 marks) (b) Describe the steps in DNA sequencing. What are its applications ? (10+5=15 marks) (c) What do you mean by signal transduction ? Explain the different types of intracellular signal transduction. (5+10=15 marks)

हिंदी में प्रश्न पढ़ें

(a) नर बंध्यता संकरओज (हेट्रोसिस) प्रजनन में किस प्रकार सहायता करती है ? संकरओज प्राप्त करने में बार्नज-बारस्टर प्रणाली के अनुप्रयोग की चर्चा कीजिए । (10+10=20 अंक) (b) डी.एन.ए. अनुक्रमण में चरणों का वर्णन कीजिए । इसके अनुप्रयोग क्या हैं ? (10+5=15 अंक) (c) संकेतक पारक्रमण (सिग्नल ट्रांसडक्शन) से आप क्या समझते हैं ? विभिन्न प्रकार के अंतरकोशिक (इंट्रासेल्युलर) संकेतक पारक्रमण की व्याख्या कीजिए । (5+10=15 अंक)

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Directive word: Discuss

This question asks you to discuss. The directive word signals the depth of analysis expected, the structure of your answer, and the weight of evidence you must bring.

See our UPSC directive words guide for a full breakdown of how to respond to each command word.

How this answer will be evaluated

Approach

The directive 'discuss' demands a balanced, analytical treatment with critical evaluation. Allocate ~40% word/time to part (a) given its 20 marks weightage, covering male sterility mechanisms and barnase-barstar molecular biology; ~30% each to parts (b) and (c). Structure: brief introduction on plant biotechnology relevance → systematic treatment of all three sub-parts with diagrams → integrated conclusion on how these techniques converge in modern crop improvement (e.g., Indian hybrid rice/maize programs).

Key points expected

  • Part (a): Genetic (cytoplasmic-nuclear) and cytoplasmic male sterility (CMS) mechanisms; how they eliminate manual emasculation, ensure cross-pollination, and maintain hybrid vigor; barnase (RNase) and barstar (inhibitor) gene system from Bacillus amyloliquefaciens; their deployment in hybrid seed production (e.g., Proagro's mustard hybrids in India)
  • Part (a): Molecular mechanism of barnase-barstar: barnase expression in tapetum causes male sterility; barstar restores fertility in maintainer/restorer lines; three-line and two-line systems in hybrid breeding
  • Part (b): Sanger (chain termination) method: template preparation, primer annealing, DNA polymerase extension with ddNTPs, capillary electrophoresis, fluorescence detection; OR Next-Generation Sequencing (Illumina) workflow: library preparation, cluster generation, sequencing-by-synthesis, data analysis
  • Part (b): Applications: genome sequencing (rice, wheat, chickpea under Indian initiatives), marker-assisted selection, functional genomics, personalized medicine, forensic identification, phylogenetic studies
  • Part (c): Signal transduction definition: extracellular signal → receptor → intracellular cascade → cellular response; types: G-protein coupled receptors (GPCRs), receptor tyrosine kinases (RTKs), steroid hormone receptors (nuclear), ion channel-linked receptors
  • Part (c): Secondary messengers: cAMP, IP3/DAG, Ca2+; MAP kinase cascades; cross-talk between pathways; specific plant examples: phytohormone signaling (auxin, ABA), pathogen recognition (PAMP-triggered immunity)

Evaluation rubric

DimensionWeightMax marksExcellentAveragePoor
Concept correctness20%10Precise definitions across all parts: distinguishes CMS from GMS in (a); accurately describes dideoxy chain termination or sequencing-by-synthesis chemistry in (b); correctly differentiates membrane-bound vs. nuclear receptors and their downstream effectors in (c); no conflation of barnase (toxin) with barstar (antidote)Generally correct definitions with minor errors: confuses CMS with GMS; oversimplifies sequencing chemistry as 'reading DNA'; describes signal transduction vaguely without receptor-effector specificity; barnase-barstar described functionally but mechanism unclearFundamental misconceptions: treats male sterility as disease; describes sequencing as 'gel running' without chemistry; conflates signal transduction with simple diffusion; barnase and barstar roles reversed or confused
Diagram / labelling20%10Three clear, labeled diagrams: (a) barnase-barstar construct showing tapetum-specific promoter (TA29) and restorer configuration; (b) Sanger sequencing gel pattern or NGS flow cell with bridge amplification; (c) GPCR or RTK signaling cascade with secondary messenger generation; all with proper molecular labels and directional arrowsTwo adequate diagrams with minor labeling gaps: basic barnase-barstar cross shown; simple sequencing ladder or vague NGS representation; linear signal pathway without feedback loops; some molecular components unnamedSingle or no diagram; poorly drawn with missing labels; generic cell diagram not specific to question; no attempt to illustrate molecular mechanisms or process steps
Examples & nomenclature20%10Specific nomenclature: CMS-T, CMS-S systems; TA29 promoter, Ri plasmid context; Indian examples: DMH-11 mustard, hybrid rice (IRRI-India collaboration), chickpea genome (ICRISAT); sequencing platforms: ABI 3730, Illumina HiSeq, Ion Torrent; plant signaling: FLS2 receptor, heterotrimeric G-proteins (GPA1), phospholipase CGeneric examples: mentions 'hybrid maize' without system; 'DNA sequencing' without method specification; 'hormone signaling' without naming specific pathways; some Indian context missing or vagueNo specific examples; incorrect nomenclature (e.g., 'barnstar' misspelled throughout); no Indian applications cited; confuses species or systems (animal signaling for plants)
Process explanation20%10Step-wise logical flow: (a) CMS establishment → maintainer line propagation → hybrid seed production with restorer; barnase expression timeline in anther development; (b) detailed Sanger protocol (denaturation, annealing, extension, termination, separation) or NGS library-to-data pipeline; (c) signal reception → transduction → amplification → response with temporal sequenceBroad process outline with gaps: hybrid breeding steps mentioned but barnase-barstar integration unclear; sequencing 'steps' listed without mechanistic detail; signaling described as 'message passed' without cascade specificityNo sequential logic; random facts listed; processes described as single events; complete absence of temporal or causal relationships between steps
Application / ecology20%10Integrated applications: (a) hybrid vigor exploitation in Indian agriculture (20-40% yield increase), biosafety considerations of barnase-barstar (gene flow concerns); (b) crop improvement through resequencing (rice 3,000 genomes project), conservation genomics, GM detection; (c) agricultural biotechnology: drought stress signaling for crop resilience, precision breeding through marker-trait associations; ecological awareness of transgene containmentGeneric applications: 'better seeds' for (a); 'medical uses' for (b); 'cell communication' for (c); some mention of Indian agriculture but not specifically linked to techniques; limited ecological or biosafety considerationNo real-world applications; purely theoretical treatment; irrelevant applications cited; complete absence of Indian agricultural context or contemporary relevance

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