Botany 2024 Paper II 50 marks Explain

Q2

(a) Explain briefly the process and importance of the following : 5+5+5=15 (i) Male sterility and heterosis breeding. 5 (ii) Molecular basis of cell cycle. 5 (iii) Gene silencing. 5 (b) Discuss briefly different methods of gene mapping. How molecular maps are of help in evulating the gene function ? 12+8=20 (c) Explain what is apomixis and how this may be of help in plant breeding ? Elaborate the answer with suitable examples. 15

हिंदी में प्रश्न पढ़ें

(a) निम्नलिखित की प्रक्रिया तथा महत्व को संक्षिप्त में स्पष्ट कीजिए : 5+5+5=15 (i) नरबंध्यता तथा संकर ओज (हेटेरोसिस) प्रजनन । 5 (ii) कोशिका चक्र का आणविक आधार । 5 (iii) जीन साइलेंसिंग । 5 (b) जीन चित्रण की विभिन्न विधियों पर संक्षिप्त में चर्चा कीजिए । आणविक मानचित्र जीन कार्यों के मूल्यांकन में कैसे सहायक होते हैं ? 12+8=20 (c) असंगजनन क्या है तथा यह पादपप्रजनन में कैसे लाभदायक है ? उत्तर को उपयुक्त उदाहरणों सहित विस्तार से लिखिए । 15

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Directive word: Explain

This question asks you to explain. 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 'explain' demands clear, logical exposition of processes and their significance. Allocate approximately 30% time/words to part (a) covering three sub-topics (5+5+5), 40% to part (b) as it carries the highest marks (12+8), and 30% to part (c) on apomixis. Structure with brief introductions for each part, systematic process explanations, and integrated examples rather than separate conclusions.

Key points expected

For (a)(i): Types of male sterility (genic, cytoplasmic, cytoplasmic-genic), their mechanisms, and role in hybrid seed production; concept of heterosis and its exploitation through CMS-based systems
For (a)(ii): Cyclins, CDKs, checkpoints (G1/S, G2/M, spindle assembly), p53 and Rb tumor suppressor roles in cell cycle regulation
For (a)(iii): RNA interference (RNAi), siRNA and miRNA pathways, post-transcriptional and transcriptional gene silencing, VIGS and its applications
For (b): Classical mapping methods (two-point and three-point test crosses, recombination frequency, mapping functions like Haldane and Kosambi) AND molecular methods (RFLP, RAPD, AFLP, SSR/SNP-based maps); use of molecular maps for positional cloning, QTL mapping, and comparative genomics
For (c): Definition of apomixis (agamospermy: adventive embryony, apospory, diplospory), genetic control (ASGR in Pennisetum), fixation of heterosis through apomictic hybrids like 'Kaveri' sorghum or citrus varieties, and limitations in breeding

Evaluation rubric

Dimension	Weight	Max marks	Excellent	Average	Poor
Concept correctness	22%	11	Precise definitions across all sub-parts: distinguishes cytoplasmic-genic male sterility from other types; correctly identifies CDK-cyclin complexes and checkpoint proteins; accurately describes RNAi mechanism with Dicer and RISC; distinguishes linkage mapping from association mapping; defines apomixis types without confusing with parthenogenesis	Generally correct definitions but conflates related concepts (e.g., mixes cytoplasmic and genic male sterility mechanisms); mentions cell cycle phases but omits key regulatory proteins; describes gene silencing superficially without pathway specificity; lists mapping methods without clear distinction	Major conceptual errors: confuses male sterility with self-incompatibility; describes mitosis/meiosis instead of cell cycle regulation; equates gene silencing with mutation; cannot distinguish classical from molecular mapping; misidentifies apomixis as vegetative propagation
Diagram / labelling	16%	8	At least 3 relevant diagrams: cell cycle with cyclin oscillations and checkpoint controls; RNAi pathway showing dsRNA→siRNA→RISC; gene mapping showing recombination or marker positions; OR schematic of apomictic vs sexual embryo sac development with proper labelling of nucellar embryo formation	One or two diagrams present but incomplete labelling; cell cycle shown as circular diagram without regulatory components; gene silencing described textually without pathway illustration; mapping shown as linear without distance calculations	No diagrams or completely unlabelled sketches; irrelevant diagrams (e.g., general plant breeding flowchart); diagrams copied without understanding, showing mitosis instead of cell cycle regulation
Examples & nomenclature	18%	9	Specific Indian/relevant examples: CMS systems in rice (WA-CMS), sorghum (A1/A2 lines), pigeonpea; cell cycle genes (cdc2, cyclin B); gene silencing in cotton bollworm resistance (Bt cotton) or papaya ringspot virus; molecular maps in rice (submergence tolerance SUB1A), wheat; apomixis in Citrus, Mangifera, or Pennisetum squamulatum with ASGR locus	Generic examples without specificity (e.g., 'maize hybrids' without naming A/B/R lines); mentions model organisms (Arabidopsis, yeast) for cell cycle but no crop applications; lists mapping techniques without citing actual crop maps; mentions apomixis in 'some grasses' without naming species	No examples or incorrect examples (e.g., apomixis in wheat which is actually sexual); confuses male sterility with self-incompatibility examples; invents non-existent gene names or mapping techniques
Process explanation	24%	12	Clear stepwise exposition: for male sterility—restorer gene action and maintenance of A/B lines; for cell cycle—sequential activation of cyclin-CDK complexes and checkpoint signalling; for RNAi—dsRNA processing, RISC assembly, and target cleavage; for gene mapping—calculation of recombination frequencies and map construction; for apomixis—meiotic modification and parthenogenetic embryo development	Describes processes in general terms without mechanistic detail; mentions 'checkpoints exist' without explaining how they function; describes mapping as 'crossing and observing' without recombination mathematics; describes apomixis as 'asexual seed formation' without developmental steps	No process explanation—only lists terms; confuses cause and effect in regulatory pathways; describes unrelated processes; complete absence of mechanistic understanding
Application / ecology	20%	10	Strong integration of theory to practice: hybrid seed industry economics and food security; cell cycle manipulation in cancer biology and crop improvement; RNAi applications in functional genomics and virus resistance breeding; molecular maps for marker-assisted selection, gene pyramiding, and genome-wide association studies; apomixis for hybrid variety fixation and preserving heterosis in marginal farmer conditions	Mentions applications superficially ('used in breeding') without elaboration; states importance without connecting to specific outcomes; generic statements about 'improving crops' without naming actual breeding programs or varieties	No application discussed; purely theoretical treatment; incorrect applications (e.g., suggesting apomixis creates new variability when it actually fixes genotypes); irrelevant ecological discussion

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