Botany 2024 Paper II 50 marks 150 words Compulsory Explain

Q1

Write short notes on the following in about 150 words each : 10×5=50 (a) Explain the types of variations found in the structure of chromosomes and discuss their importance and significance. 10 (b) Explain with at least two examples what is incomplete dominance and polygenic inheritance and what happens as a result of these events ? 10 (c) Discuss what are cell receptors and how do they help in cell signalling ? Elaborate the answer with the help of at least one example. 10 (d) Discuss with one example the role of RNA in the origin and evolution of life. 10 (e) Probability and distribution are two important factors which should always be taken into account to establish a successful breeding programme. Explain with a suitable example. 10

हिंदी में प्रश्न पढ़ें

निम्नलिखित में से प्रत्येक पर लगभग 150 शब्दों में संक्षिप्ट टिप्पणियाँ लिखिए : 10×5=50 (a) गुणसूत्रों की संरचना में पाए जाने वाले बदलाव के प्रकार को स्पष्ट कीजिए तथा उनके महत्व एवं उपयोगिता का वर्णन कीजिए । 10 (b) कम से कम दो उदाहरणों सहित स्पष्ट कीजिए, अधूरा प्रभुत्व तथा पॉलीजेनिक वंशागति क्या है तथा इनके परिणाम स्वरूप क्या होता है ? 10 (c) कोशिका ग्राही (रिसेप्टर्स) क्या हैं वर्णन कीजिए तथा वे कोशिका सिग्नलिंग में कैसे सहायता करते हैं ? कम से कम एक उदाहरण सहित उत्तर को विस्तार से लिखिए । 10 (d) कम से कम एक उदाहरण सहित जीव की उत्पत्ति तथा विकास में आर.एन.ए. की भूमिका का वर्णन कीजिए । 10 (e) प्रायिकता तथा वितरण दो महत्वपूर्ण कारक हैं जिन्हें सफल प्रजनन कार्य को स्थापित करने के लिए हमेशा ध्यान में रखना चाहिए । उपयुक्त उदाहरण सहित स्पष्ट कीजिए । 10

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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 conceptual clarity with cause-effect linkages across all five parts. Allocate approximately 30 words per sub-part (150 total), spending roughly equal time on each since all carry 10 marks. Structure each note as: definition → mechanism → significance/example. For (a), prioritize structural variation types with their cytogenetic consequences; for (b), contrast incomplete dominance (qualitative) with polygenic inheritance (quantitative); for (c), emphasize receptor-ligand binding and signal transduction cascade; for (d), focus on RNA world hypothesis with catalytic RNA evidence; for (e), apply probability rules to breeding outcomes. No introduction or conclusion needed—jump directly into each sub-part.

Key points expected

  • (a) Structural variations: deletion, duplication, inversion, translocation; importance in evolution, speciation, and genetic disorders (e.g., Philadelphia chromosome in CML)
  • (b) Incomplete dominance: Mirabilis jalapa (4 O'clock plant) flower color; polygenic inheritance: wheat kernel color/Human skin color; continuous variation vs. discrete phenotypes
  • (c) Cell receptors: membrane-bound (GPCRs, RTKs) and intracellular receptors; signal transduction via second messengers (cAMP, Ca2+); example: insulin receptor tyrosine kinase pathway
  • (d) RNA world hypothesis: ribozymes, self-splicing introns, ribosomal RNA catalytic activity; example: Tetrahymena self-splicing intron or peptidyl transferase activity of 23S rRNA
  • (e) Probability in breeding: Mendelian ratios, chi-square test for goodness of fit; distribution: normal distribution of polygenic traits; example: predicting F2 segregation ratios or heritability calculations in wheat breeding
  • Nomenclature accuracy: proper genetic symbols, chromosome banding terminology, receptor classification
  • Comparative framing: contrasting structural vs. numerical chromosomal changes; incomplete dominance vs. codominance; qualitative vs. quantitative inheritance
  • Evolutionary and agricultural significance: connecting molecular mechanisms to crop improvement and evolutionary theory

Evaluation rubric

DimensionWeightMax marksExcellentAveragePoor
Concept correctness25%12.5Precise definitions across all parts: correctly distinguishes pericentric vs. paracentric inversion in (a); accurately contrasts additive gene action vs. dominance deviation in (b); correctly identifies receptor domains and downstream signaling in (c); accurately describes RNA catalytic properties and evolutionary transition to DNA-protein world in (d); applies probability rules (product and sum) correctly in (e). No conceptual conflation between incomplete dominance and codominance.Generally correct definitions with minor errors: confuses Robertsonian translocation with reciprocal translocation; oversimplifies polygenic inheritance as 'many genes'; describes signal transduction vaguely without specifying kinase cascades; mentions RNA world without catalytic evidence; calculates probability correctly but without showing Punnett square or formula.Fundamental errors: confuses structural with numerical chromosomal changes; describes incomplete dominance as 'blending inheritance'; conflates receptors with carrier proteins; describes RNA only as messenger without catalytic role; applies probability incorrectly or uses wrong distribution for genetic data.
Diagram / labelling15%7.5Includes at least 2-3 schematic diagrams: chromosome structural variations with breakpoints labelled (a); Punnett square or bell curve for polygenic traits (b); receptor-ligand binding with conformational change (c); RNA secondary structure with catalytic site (d); probability distribution curve or branching diagram for breeding (e). Labels are precise and diagram supports explanation.Includes one diagram or rough sketches without proper labels; diagrams are generic rather than specific to the example cited; labels incomplete or arrows unclear; diagrams mentioned in text but not clearly drawn.No diagrams despite visualizable content; or diagrams completely wrong (e.g., drawing meiosis for chromosome structural variation); labels missing or misleading; diagrams contradict written explanation.
Examples & nomenclature20%10Specific, accurate examples: (a) Cri-du-chat syndrome (5p deletion), Burkitt lymphoma (8;14 translocation); (b) Antirrhinum majus or Mirabilis jalapa for incomplete dominance, human skin color or wheat grain color for polygenic; (c) specific G-protein coupled receptor or insulin receptor with correct subunit names; (d) Tetrahymena ribozyme or RNase P with discoverer (Cech/Altman); (e) specific Indian crop example (e.g., rice yield improvement at IRRI or Indian wheat varieties). Standard genetic and cytogenetic nomenclature throughout.Examples given but generic or partially inaccurate: mentions 'cancer' without specific chromosomal abnormality; gives one example each for dominance and polygenic but second example missing or vague; receptor example without specificity; RNA world mentioned without specific molecule; breeding example without numerical probability demonstration.No specific examples or wrong examples: cites sickle cell anemia for incomplete dominance; gives Lamarckian example for evolution; examples contradict the concept explained; no Indian or standard international examples; invented or confused nomenclature.
Process explanation20%10Clear mechanistic flow: for (a), how breakage-reunion leads to each structural change and consequences for pairing/segregation; for (b), biochemical basis of intermediate phenotype and additive effects producing continuous variation; for (c), sequential steps from ligand binding to receptor activation to cellular response; for (d), stepwise transition from RNA catalysts to DNA genomes and protein enzymes; for (e), step-by-step probability calculation with proper statistical reasoning.Describes processes in static terms without dynamic mechanism; mentions steps but not their sequence or causal relationships; explains 'what happens' without 'how it happens'; some processes described well, others superficially across the five parts.No process explanation or completely garbled sequence; describes outcomes without any mechanism; confuses cause and effect; processes described are biologically impossible or violate central dogma; no mention of molecular mechanisms.
Application / ecology20%10Explicit significance statements: (a) role in evolution, speciation, and clinical cytogenetics; (b) agricultural importance of heterosis and selection for quantitative traits; (c) therapeutic targeting of receptors, drug design; (d) implications for origin of life research and synthetic biology; (e) practical breeding strategies, heritability estimation, and marker-assisted selection in Indian agriculture. Connects basic biology to societal benefit.Mentions significance superficially ('important in evolution') without elaboration; applications stated without specificity; some parts have clear application, others none; generic statements about 'helping farmers' without mechanism.No significance or application discussed; or completely misidentifies significance (e.g., structural variations 'cause DNA replication'); applications are irrelevant or factually wrong; misses evolutionary and agricultural context entirely.

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