Botany 2023 Paper II 50 marks Differentiate

Q2

(a) Differentiate between polytene chromosomes and normal chromosomes. 15 (b) Describe polygenic inheritance by giving suitable examples. 15 (c) Describe the problems associated with gene transfer in plants. Write a note on the status of transgenic research in India. 15+5=20

हिंदी में प्रश्न पढ़ें

(a) बहुपट्टीय गुणसूत्र एवं सामान्य गुणसूत्र में विभेद कीजिए । 15 (b) उपयुक्त उदाहरणों को देते हुए अनेकजीनी वंशागति का वर्णन कीजिए । 15 (c) पादपों में जीन स्थानांतरण (जीन ट्रांसफर) से जुड़ी समस्याओं का वर्णन कीजिए । भारत में पारजीनी अनुसंधान की स्थिति पर एक टिप्पणी लिखिए । 15+5=20

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Directive word: Differentiate

This question asks you to differentiate. 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 'differentiate' in part (a) demands clear comparative analysis, while parts (b) and (c) require descriptive exposition. Allocate approximately 30% time/words to part (a) given its 15 marks and comparative nature, 30% to part (b) for detailed polygenic explanation with examples, and 40% to part (c) as it combines two elements (15+5 marks). Structure as: brief introduction → systematic treatment of (a), (b), (c) with clear sub-headings → concluding synthesis on chromosome research and transgenic applications in Indian agriculture.

Key points expected

  • Part (a): Polytene chromosomes show endoreduplication without cell division, forming giant chromosomes with visible banding patterns (chromomeres), contrasting with normal mitotic chromosomes; mention occurrence in Drosophila salivary glands and their use in cytogenetic mapping
  • Part (b): Polygenic inheritance involves multiple genes with additive effects producing continuous variation; exemplify with kernel colour in wheat (Nilsson-Ehle), human skin colour, or plant height in tobacco; contrast with Mendelian monogenic ratios
  • Part (c): Gene transfer problems include position effects, gene silencing, pleiotropic effects, antibiotic resistance marker concerns, pollen-mediated gene flow to wild relatives, and regulatory challenges; cite Bt cotton, Bt brinjal controversy, and current status under GEAC/RCGM with examples like GM mustard (DMH-11)
  • Part (c) continued: Indian transgenic research status requires mention of institutional framework (DBT, MoEFCC), commercialized crops (Bt cotton since 2002), field trials moratorium context, and biosafety regulatory evolution
  • Integration: Connect polytene chromosome research (giant chromosome mapping) to modern transgenic techniques; note how understanding chromosome structure aids gene insertion site selection

Evaluation rubric

DimensionWeightMax marksExcellentAveragePoor
Concept correctness22%11Precisely defines endoreduplication mechanism in polytene formation; correctly distinguishes qualitative vs. quantitative inheritance; accurately identifies somaclonal variation, position effects, and co-suppression as gene transfer problems; names correct regulatory bodies (GEAC, RCGM) and their jurisdictionBasic distinction between chromosome types without mechanistic detail; general description of polygenic inheritance without mathematical basis; lists generic problems like 'low efficiency' without specificity; mentions Bt cotton but confuses regulatory historyConfuses polytene with lampbrush chromosomes or polyploidy; describes polygenic as 'many genes' without additive effect explanation; conflates gene transfer with tissue culture problems; factual errors on Indian GMO policy timeline
Diagram / labelling18%9Draws labeled polytene chromosome showing chromomeres, interchromomeric regions, and puffing; includes normal metaphase chromosome for comparison; sketches polygenic distribution curve with parental, F1, F2 generations; illustrates gene transfer methods (Agrobacterium/ particle bombardment) with T-DNA border sequencesSimple diagram of giant chromosome without structural details; basic bell curve for polygenic distribution; generic plant transformation diagram without mechanism labels; diagrams present but incompletely integrated with textNo diagrams despite visual nature of question; mislabeled chromosome structures; diagrams copied without explanation; irrelevant illustrations (e.g., DNA double helix instead of chromosomes)
Examples & nomenclature20%10Cites Drosophila melanogaster salivary glands for polytene; Nilsson-Ehle's wheat kernel colour (3:1:3:1:7:1:15:1:... ratios) or East's tobacco for polygenic; names specific Indian transgenic developments (Bt cotton hybrids like MECH-162, RCH2; GM mustard DMH-11; biosafety guidelines 1990, 1994, 1998 revisions)General mention of 'fruit flies' and 'wheat' without specific experiments; human height/skin colour as polygenic examples; Bt cotton mentioned without hybrid names; generic reference to 'many GM crops in trials'Incorrect examples (e.g., polyploidy for polytene); no Indian-specific instances; outdated or invented regulatory information; confuses transgenic with conventional breeding examples
Process explanation22%11Explains endoreduplication cycle (S-phase without M-phase) producing 1024-2048 chromatids; details polygenic inheritance mathematics (1/4ⁿ, 2/4ⁿ, etc. for n gene pairs); elaborates Agrobacterium-mediated transformation mechanism, vector construction, and T-DNA integration; explains gene silencing mechanisms (RNAi, methylation)States polytene chromosomes are 'replicated many times' without cell cycle detail; describes polygenic as 'blending inheritance' without statistical basis; lists transformation steps without molecular mechanism; mentions 'safety concerns' without process explanationNo mechanistic explanation for any part; confuses processes (e.g., crossing over with endoreduplication); describes transformation as 'injecting genes' without biological basis; ignores molecular aspects entirely
Application / ecology18%9Links polytene puffs to gene activation studies; connects polygenic analysis to crop improvement and heritability calculations; evaluates ecological risks (gene flow to wild Oryza nivara, Brassica rapa); critically assesses Indian regulatory framework evolution, farmer suicides debate, and socio-economic impacts of Bt cotton adoptionMentions polytene use in mapping without modern applications; states polygenic importance in breeding without methodology; lists biosafety concerns without ecological context; descriptive account of Indian GMO policy without critical evaluationNo application or ecological dimension; ignores 20 marks explicitly on problems and Indian status; purely theoretical treatment; no mention of environmental release, biodiversity, or socio-economic factors

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