Botany 2022 Paper II 50 marks Discuss

Q3

(a) What is organic evolution ? Highlight the mechanisms governing organic evolution. (5+10=15 marks) (b) Explain the phenomenon of incomplete dominance and its significance. (10+5=15 marks) (c) What is gene editing ? Discuss its applications and advantages for genetic engineering. (10+10=20 marks)

हिंदी में प्रश्न पढ़ें

(a) जैविक विकास क्या है ? जैविक विकास को नियंत्रित करने वाले तंत्र पर प्रकाश डालिए । (5+10=15 अंक) (b) अपूर्ण प्रभाविता की परिघटना और इसके महत्व की व्याख्या कीजिए । (10+5=15 अंक) (c) जीन एडिटिंग क्या है ? आनुवंशिक अभियांत्रिकी में इसके अनुप्रयोगों और लाभों पर चर्चा कीजिए । (10+10=20 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' for part (c) demands critical examination with multiple perspectives, while parts (a) and (b) require 'highlight' and 'explain' respectively. Allocate approximately 30% time/words to part (a) on organic evolution, 30% to part (b) on incomplete dominance, and 40% to part (c) on gene editing given its higher mark weightage. Structure with a brief introduction connecting evolutionary mechanisms to genetic principles, then address each sub-part sequentially with clear sub-headings, and conclude with synthesis on how gene editing extends our understanding of evolutionary mechanisms.

Key points expected

  • Part (a): Definition of organic evolution as descent with modification; mechanisms including natural selection, genetic drift, gene flow, mutation, and non-random mating with their relative contributions
  • Part (a): Distinction between microevolution and macroevolution; role of Hardy-Weinberg equilibrium as null hypothesis for evolutionary change
  • Part (b): Incomplete dominance in Mirabilis jalapa (4 o'clock plant) or Antirrhinum majus; phenotypic ratio 1:2:1 distinguishing it from codominance
  • Part (b): Molecular basis involving intermediate enzyme levels; significance in maintaining genetic variation and evolutionary potential
  • Part (c): CRISPR-Cas9 mechanism with guide RNA and PAM site recognition; distinction from earlier techniques (ZFNs, TALENs)
  • Part (c): Applications in crop improvement (Golden Rice 2, Bt brinjal development), disease resistance, and therapeutic genome editing
  • Part (c): Advantages including precision, efficiency, multiplexing capability, and cost-effectiveness; ethical considerations and regulatory framework in India

Evaluation rubric

DimensionWeightMax marksExcellentAveragePoor
Concept correctness20%10Precise definitions across all parts: organic evolution distinguished from chemical evolution; incomplete dominance correctly differentiated from codominance and epistasis; CRISPR mechanism accurately described with Cas9 nuclease function and DSB repair pathwaysGenerally correct definitions with minor confusions; may conflate incomplete dominance with codominance or misstate CRISPR as RNAi; evolutionary mechanisms listed without clear distinctionsFundamental errors such as defining evolution as 'progress' or 'Lamarckian'; confusing incomplete dominance with blending inheritance; describing gene editing as 'cutting DNA with enzymes' without specificity
Diagram / labelling15%7.5Clear diagrams for part (b) showing parental, F1, and F2 generations with phenotypic ratios; part (c) diagram of CRISPR-Cas9 complex with sgRNA, PAM site, and DSB; proper labelling of all componentsBasic Punnett square for incomplete dominance without phenotypic illustration; simplified CRISPR diagram missing key components like tracrRNA or repair mechanismsNo diagrams or incorrect diagrams; confusing evolutionary tree with phylogenetic relationships; misrepresenting gene editing as restriction enzyme digestion
Examples & nomenclature20%10Specific examples: Mirabilis jalapa/Antirrhinum for incomplete dominance; Indian examples like CRISPR-edited banana for Fusarium resistance, drought-tolerant rice varieties; correct nomenclature (Cas9, sgRNA, HDR, NHEJ)Generic examples like 'flowers' for incomplete dominance; international examples without Indian context; partial nomenclature with some technical terms misspelledNo specific examples or invented examples; incorrect nomenclature (e.g., 'CRISPR-Cas13' for standard gene editing); confusing gene editing with genetic modification by transgenesis
Process explanation25%12.5Stepwise mechanisms: for (a) how mutation-selection balance maintains variation; for (b) molecular basis of intermediate phenotype through enzyme dosage; for (c) detailed CRISPR workflow from design to validation including off-target assessmentSequential but superficial coverage; lists evolutionary mechanisms without explaining interactions; describes CRISPR steps without explaining molecular basis of target recognitionNo logical flow; random facts without process linkage; fundamental misunderstanding of how CRISPR achieves specificity or how incomplete dominance produces 1:2:1 ratio
Application / ecology20%10Ecological significance of evolutionary mechanisms in adaptation; agricultural applications of incomplete dominance in heterosis; comprehensive coverage of gene editing applications in Indian agriculture (biofortification, climate resilience) with biosafety and ethical dimensionsMentions applications without depth; generic statements about 'feeding the world'; limited awareness of Indian regulatory framework (GEAC, RCGM) or Cartagena Protocol implicationsNo application dimension; purely theoretical treatment; ignores ethical concerns or presents gene editing as unproblematic; no connection between genetic mechanisms and evolutionary outcomes

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