Zoology 2024 Paper II 50 marks 150 words Compulsory Write short notes

Q1

Write on the following in about 150 words each: (a) Polytene chromosome (10 marks) (b) Difference between male heterogamety and female heterogamety with examples (10 marks) (c) Types of chromosomal aberrations (10 marks) (d) Geographic versus reproductive isolation (10 marks) (e) Main types of molecular mutations and their effect on phenotype (10 marks)

हिंदी में प्रश्न पढ़ें

निम्नलिखित प्रत्येक पर लगभग 150 शब्दों में लिखिए : (a) बहुपट्टी गुणसूत्र (10 अंक) (b) उदाहरण सहित नर विषमयुग्मनी (हेट्रोगैमिटी) एवं मादा विषमयुग्मनी के बीच अंतर (10 अंक) (c) गुणसूत्री विपथन के प्रकार (10 अंक) (d) भौगोलिक बनाम प्रजननात्मक पृथक्करण (10 अंक) (e) आणविक उत्परिवर्तन के मुख्य प्रकार तथा लक्षणप्ररूप (फीनोटाइप) पर उनका प्रभाव (10 अंक)

Evaluate your answer to this question → See all 2024 Zoology questions

Directive word: Write short notes

This question asks you to write short notes. 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

Write short notes demands concise, information-dense responses without elaborate introductions. Allocate approximately 30 words per mark (150 words × 5 parts = 750 total). Spend roughly equal time on each sub-part (a-e) as all carry equal marks; begin each part with a crisp definition, follow with 2-3 distinguishing features or types, and end with a specific Indian/global example where applicable. No conclusion needed; maximize factual density within word limits.

Key points expected

(a) Polytene chromosome: Define as giant chromosomes from repeated DNA replication without cell division; mention salivary glands of Drosophila; note chromosomal puffing as gene activation sites; cite Balbiani rings and their use in gene mapping
(b) Male vs female heterogamety: Contrast XY/XX system (Drosophila, humans) with ZW/ZZ system (birds, butterflies); specify which sex produces heteromorphic gametes; mention Indian examples like silkworm (Bombyx mori) for ZW system
(c) Chromosomal aberrations: Distinguish structural (deletion, duplication, inversion, translocation) from numerical (euploidy, aneuploidy); mention specific human disorders like Down syndrome (trisomy 21), Cri-du-chat syndrome
(d) Geographic vs reproductive isolation: Define allopatric speciation through physical barriers (Himalayan uplift separating populations) versus prezygotic/postzygotic barriers; cite Indian examples like Western Ghats endemic species
(e) Molecular mutations and phenotype effects: Classify as substitution (missense, nonsense, silent), frameshift (insertion, deletion); explain how synonymous mutations may not alter phenotype while nonsense mutations truncate proteins; cite sickle cell anemia (β-globin Glu→Val)

Evaluation rubric

Dimension	Weight	Max marks	Excellent	Average	Poor
Concept correctness	20%	10	All five sub-parts demonstrate accurate core concepts: correctly identifies polytene chromosomes as endoreduplication products; precisely distinguishes heterogametic sex in XY versus ZW systems; accurately categorizes aberration types; correctly differentiates extrinsic versus intrinsic isolating mechanisms; properly classifies molecular mutation types by DNA-level change	Most concepts correctly stated but with minor errors: confuses ZW system sex determination direction; conflates structural and numerical aberration examples; vague on whether geographic isolation is a subset or distinct from reproductive isolation	Fundamental conceptual errors: describes polytene chromosomes as meiotic products; reverses heterogamety in XY and ZW systems; treats all mutations as having phenotypic effects; fails to distinguish between isolation types
Diagram / labelling	15%	7.5	Includes at least two well-executed diagrams: polytene chromosome showing banding pattern and puff; clear schematic comparing XY and ZW sex determination; OR chromosomal aberration types (ideogram showing deletion/duplication/inversion/translocation); labels are precise and exam-appropriate	One relevant diagram attempted but incomplete: polytene chromosome drawn without indicating puffs; sex chromosome schematic lacks gamete formation arrows; aberration diagram present but translocation incorrectly depicted	No diagrams or completely inaccurate sketches; labels missing or wrong; diagrams unrelated to question content; wastes space with decorative but non-informative illustrations
Examples & nomenclature	20%	10	Specific, diverse examples across all parts: Drosophila salivary glands and Chironomus for polytene; Homo sapiens, Drosophila melanogaster for XY; Gallus domesticus, Bombyx mori for ZW; Down syndrome, Turner syndrome for aberrations; Western Ghats salamanders or Himalayan langurs for geographic isolation; sickle cell anemia, β-thalassemia for molecular mutations; scientific names italicized correctly	Generic examples only: mentions 'fruit fly' without species name; 'humans' for XY but no ZW example; 'birds' without specific species; common disorders named but without chromosomal specification; no Indian examples	No specific examples or incorrect ones: states 'all animals have XY system'; confuses geographic and reproductive isolation examples; cites Lamarckian or non-genetic examples; scientific names incorrectly formatted or misspelled
Process explanation	25%	12.5	Clear mechanistic explanations: for (a) explains endoreduplication cycle (S phase without M phase); for (b) details meiotic segregation patterns producing unequal gamete ratios; for (c) describes how non-disjunction creates aneuploidy and how breakage-fusion-bridge cycles cause structural changes; for (d) explains how geographic barriers lead to divergent selection and reproductive character displacement; for (e) clarifies codon degeneracy and reading frame maintenance	Static descriptions without mechanisms: states polytene chromosomes are 'large' without explaining why; lists heterogamety types without explaining gamete formation; names aberration types without describing origin; describes isolation as 'preventing breeding' without speciation mechanism; mentions mutation types without explaining molecular consequences	No process understanding: describes polytene chromosomes as 'mutated chromosomes'; presents heterogamety as arbitrary sex assignment; treats chromosomal aberrations as always inherited; cannot explain how geographic isolation leads to reproductive isolation; conflates all mutation types as equally damaging
Evolutionary / applied context	20%	10	Explicit evolutionary and applied significance: polytene puffs as gene expression windows for developmental studies; heterogamety systems in sex-ratio manipulation and conservation genetics (Indian crocodile temperature-dependent sex determination context); chromosomal aberrations in speciation (Indian muntjac chromosome evolution) and prenatal diagnosis; reproductive isolation as speciation mechanism; molecular mutations as raw material for selection and basis of genetic disorders with Indian prevalence data	Brief mention of significance without depth: notes polytene chromosomes are 'useful for study'; states heterogamety 'determines sex'; mentions aberrations 'cause disease'; notes isolation 'prevents gene flow'; states mutations 'change traits'	No evolutionary or applied context: treats all topics as isolated facts; misses that polytene chromosomes revolutionized cytogenetics; fails to connect heterogamety to sex chromosome evolution; ignores that chromosomal changes drive macroevolution; no mention of mutation in adaptation or disease

Practice this exact question

Write your answer, then get a detailed evaluation from our AI trained on UPSC's answer-writing standards. Free first evaluation — no signup needed to start.

Evaluate my answer →