Principles of Inheritance and Variation
Class 12 Biology · Biology · Chapter 4
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Physics, Chemistry, Maths + English
88 Class 12 PCM kits: what the board asked
- Physics: 35 marks for Ray Optics, four papers
- Maths: 35 marks for Integrals, four papers
- Maths: 35 marks in the Calculus unit
- Chemistry: 9 marks in Electrochemistry
- Chemistry: seven board sums, worked stepwise
- English: 13 Flamingo texts, what 2025 asked
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Physics, Chemistry, Biology + English
7 Class 12 PCB kits: what the board asked
- Biology: 20 marks in Unit VII, the biggest
- Physics: 35 marks for Ray Optics, four papers
- Physics: 32 marks for Capacitance, 4 papers
- Chemistry: 9 marks in Electrochemistry
- Biomolecules: 7 marks in every paper
- English: 13 Flamingo texts, what 2025 asked
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Accountancy, Business Studies, Economics + English
99 Class 12 Commerce kits: what the board asked
- Accountancy: 65 marks for Admission, 4 papers
- Accountancy: all 18 ratios, the book's answers
- Business Studies: 37 marks for Directing
- Economic Development: 20 marks in Unit 7
- Macroeconomics: 12 marks in Ch 4, the lead
- English: 13 Flamingo texts, what 2025 asked
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Biology
Genetics + Evolution: Unit VII, 20 marks
- 16 marks: Reproduction, Unit VI
- 12 marks each: Units VIII and IX
- 10 marks: Ecology, Unit X
- 13 chapters, with page numbers
- Common traps, corrected
- Final test with answers
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Physics
Both Physics parts: marks from four papers
- 35 marks: Ray Optics across four papers
- 32 marks: Capacitance in 4 papers
- 34 marks: Magnetism, Ch 4–5, in 4 papers
- 33 marks: Induction and AC in 4 papers
- 7 marks: Semiconductors in all four papers
- 12-question test in both kits
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History
3All 3 History parts: board marks by theme
- 35 of 100 marks: Kings, Farmers and Towns
- 26 of 100 each: Travellers and Bhakti-Sufi
- 24 of 100 each: Vijayanagara, Mughal village
- 25 theory marks: Themes 9–12, 1793 to 1950
- Q24 from Vijayanagara in every 2025 set
- A final test in all three kits
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Hindi Elective
2अंतरा + अंतराल: lessons, marks, answer frames
- 17 अंतरा lessons, each with its board marks
- 38 board marks: अंतरा prose 4–8
- 3 अंतराल lessons, three model 5-mark answers
- 22 marks: खंड ख, covered in both kits
- 17 writers on one timeline
- 12 mistakes + 12-question test in both kits
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Mathematics
2Both Maths parts: what the board papers asked
- 35 marks: Integrals across the four papers
- 35 marks: the Calculus unit; Algebra: 10
- 23 marks: Vectors across the four papers
- Part I: every 2025 and SQP question
- Integral tables + properties P0–P7
- 14-question test in both kits
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Sociology
2Both Sociology books: the examined chapters
- 10 marks each: Indian Society Ch 2, 3, 5, 6
- 5 examined chapters in Social Change
- 10 marks each: Units 11, 12 and 15
- 2025 questions mapped to Social Change
- Demography formulas, sex-ratio, age tables
- A final test in both kits
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Economics
2Both Economics books: marks, unit by unit
- 12 marks: Macro Ch 4, the biggest unit
- 10 marks: National Income Accounting
- 20 marks: Unit 7 of Economic Development
- GDP by three methods, M1–M4, multiplier
- India, China and Pakistan compared
- 12-question test in both kits
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Home Science
2Both Home Science parts: 2025 Qs, by chapter
- 38 of the 70 theory marks: Part I
- 32 of the 70 theory marks: Part II
- 23 marks: Unit II, nutrition and food
- 17 marks: Fabric and Apparel
- 2025 board and SQP questions, by chapter
- Traps and a final test in both kits
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Urdu Elective
2Both Urdu Elective books: writers to answers
- 20 گلستانِ ادب lessons, 14 writers, 9 genres
- 13 literary terms and devices
- Three translated stories in Khayaban-e-Urdu
- 12 book answers for the three stories
- Chekhov, Basheer, Nirmal Verma introduced
- 10 common mistakes + 10 questions
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Geography
3All 3 Geography books: marks and map items
- 48 CBSE India map items, by chapter
- 18 of 120 marks asked: Human Development
- 20 marks in 4 papers: Ch 1 Population
- 30 practical marks: where each one sits
- 13 of the 28 map items asked: Minerals
- A final test in all three kits
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Accountancy
All 3 Accountancy kits: what the board asked
- 65 marks in 4 papers: Admission of a Partner
- 36 of 80 theory marks: Partnership
- 18 ratios, with the book's answers
- 15 marks in every 2025 set: share capital
- 56 of 105 Option II marks: Spreadsheet
- 6-mark cash flow in every paper
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English Core
2Flamingo + Vistas: texts, formats, passages
- 13 Flamingo texts, with what 2025 asked
- 5 poems: Q7 is always one of these
- 4 writing formats, 18 marks
- 13 Vistas marks: characters with quotes
- 22 unseen-passage marks: both types decoded
- Traps + 12-question test in both kits
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Political Science
2Both Political Science books: 40 marks each
- 4 of 4 papers asked End of Bipolarity
- 3 of 4 papers: the 6-marker from Security
- 4-marker on Environment in all 4 papers
- 8 marks: Ch 8 of Politics in India, 1989–2019
- State-formation and war timelines
- Dates, treaties, leaders in tables
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Chemistry
2Both Chemistry parts: marks, unit by unit
- 9 marks: Electrochemistry, Part I's biggest
- 8 marks: Unit 8 carbonyls, Part II's biggest
- 7 marks: Biomolecules, in every paper
- Seven board sums, worked stepwise
- Named reactions, reagents, conditions
- 12-question test in both kits
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Business Studies
2Both Business Studies parts: what was asked
- 37 marks in 4 papers: Directing
- 8 Part I chapters, ranked by what was asked
- 31 marks: Organising, a 6-marker every set
- 26 marks across 4 papers: Financial Markets
- 14 principles of Fayol + case cues
- Consumer Protection Act 2019 tiers
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Hindi Core
2आरोह + वितान: board asks and answer frames
- 15 आरोह lessons, board asks by lesson
- 30 marks of आरोह: answer frames
- 10 marks: वितान's Q12, with 9 board questions
- 22 marks: Section B formats
- 15 writers on a timeline
- 12 mistakes + 12-question test in both kits
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Mathematics
Every Part I question from 2025 + the SQP
- 35 marks: Calculus, shared with Part II
- 10 marks: Algebra, Ch 3–4
- 6 principal branches of inverse trig
- Every derivative rule with its condition
- Marking-scheme templates for board methods
- 14-question final test with answers
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हिंदी (आधार)
All 15 आरोह lessons, board asks by lesson
- 30 marks: answer frames for आरोह
- 40 marks outside the book, mapped
- 15 writers on one timeline
- Unseen passage question types
- 12 common mistakes, corrected
- 12-question final test with answers
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Accountancy
Spreadsheet: 56 of 105 Option II marks
- 22 of 105 marks on offer: CAS overview
- Most asked item: error values
- What Q27–34 ask, answer by answer
- Every Excel function, result checked
- 12 common traps, corrected
- 15-question final test with answers
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اردو (اختیاری)
20 گلستانِ ادب lessons, 14 writers
- 13 literary terms and devices
- 9 genres, each defined
- Writers' dates and works, by page
- Five ghazals and four nazms covered
- 10 common mistakes, corrected
- 10-question final test
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Mathematics
Integrals: 35 marks across the four papers
- 23 marks in the four papers: Vector Algebra
- Integral tables with properties P0–P7
- 3 methods for differential equations
- 8 marks: Probability, with Bayes' theorem
- Patterns the board repeats, by chapter
- 14-question final test with answers
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हिंदी (आधार)
वितान: Q12's 10 marks, answer frames
- 9 board questions in one place
- 22 marks: Section B formats
- 3 lessons: characters and symbols for each
- Event order for each lesson, with pages
- 12 common mistakes
- 12-question final test with answers
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संस्कृतम् (केन्द्रिकम्)
All 8 भास्वती lessons: who says what to whom
- 20 marks: grammar, 4 × 1 per part
- Sandhi, samasa, pratyaya from the text
- Upapada-vibhakti and vachya examples
- Anvaya and bhavartha answer method
- Literature intro: epics, prose, champu
- 12-question final test with answers
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Physics
Capacitance: 32 marks in 4 papers, most asked
- 34 marks in 4 papers: Magnetism, Ch 4–5
- 33 marks in 4 papers: Induction and AC
- 26 marks in 4 papers: Current Electricity
- Every formula with its page number
- What each 2025 board paper asked
- 12-question final test with answers
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हिंदी (ऐच्छिक)
All 17 अंतरा lessons, with board marks
- 38 board marks: prose 4–8
- 37 board marks: poems 1–5
- 22 marks: खंड ख, with answer frames
- 17 writers on one timeline
- 12 common mistakes, corrected
- 12-question final test with answers
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संस्कृत (ऐच्छिक)
शाश्वती: where the 25 + 10 + 10 marks sit
- 15 marks: grammar from the lessons
- 6 metres with their gana-sutras
- 6 figures of speech (अलङ्कार)
- 20 shlokas of रघुकौत्ससंवादः, upajati metre
- Literary history in tables, epic to drama
- 12-question final test with answers
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Physics
TrendingRay Optics: 35 marks across four papers
- 22 marks across four papers: Wave Optics
- 22 marks: Dual Nature, with 4-mark cases
- 13 marks each: Atoms and Nuclei
- 7 marks in all four papers: Semiconductors
- 5-marker: prisms, microscopes, telescopes
- 12-question final test with answers
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हिंदी (ऐच्छिक)
All 3 अंतराल lessons + खंड ख (22 marks)
- 7 exercise, 3 board answers for lesson 1
- 5-mark answers in about 100 words
- Three model 5-mark answers
- Malwa's rivers and rainfall figures
- 12 common mistakes, corrected
- 12-question final test with answers
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اردو (کور)
11 نئی آواز lessons + the board's idioms
- Author, genre and summary, lesson by lesson
- Verse meanings: پرچھائیاں, اپنے گھر کا حال
- Essay, letter and precis writing
- Map of the question paper
- 8 common mistakes
- 12-question final test with answers
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Chemistry
Electrochemistry: 9 marks, biggest unit
- 7 marks each: the other four units
- 37 of 70 theory marks across 5 units
- Seven board sums, worked stepwise
- Every data table, with page numbers
- Mixed traps, corrected
- 12-question final test with answers
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Urdu Elective
Three translated stories, 12 book answers
- Chekhov, Basheer and Nirmal Verma introduced
- کلرک کی موت: 1 sneeze, 5 apologies
- Event order and characters for each story
- 3 stories compared in one table
- Method for writing board answers
- 8-question final test with answers
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Computer Science
Files, stack, functions: Unit 1, 40 marks
- 20 marks: SQL and databases, Unit 3
- 10 marks: Networks, Unit 2
- 7 chapters: every output run and checked
- Stack algorithms and output questions
- Text, binary and CSV file programs
- Final test with answers
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Chemistry
Unit 8 carbonyls: 8 marks, biggest unit
- 7 marks in every paper: Biomolecules
- 6 marks in each 2025 set: Haloalkanes
- 4–5-mark question every paper: Alcohols
- Named reactions, reagents, conditions
- Tests that tell compounds apart
- 12-question final test with answers
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Fine Art · Painting
TrendingAll 29 prescribed works: painter to medium
- 24 of 92 board marks: Bengal School
- 20 of 92 board marks: Mughal School
- 17 of 92 board marks: Rajasthani Schools
- 11 of 92: modern art, mostly 2-markers
- 2025 paper and SQP, question by question
- 12-question final test with answers
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हिंदुस्तानी संगीत (गायन / वादन)
15 gamak, 14 murchhana, three ragas
- 30 theory marks, all five units
- Bhairav, Bageshri, Malkauns in full
- Jhaptal, Rupak, Dhamar: dugun to chaugun
- Sangeet Ratnakar and Parijat, by chapter
- Tuning the tanpura and the sitar
- 12-question final test with answers
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Informatics Practices
Pandas: 38 of 140 board marks, mapped
- 35 of 140 board marks: SQL functions
- 20 board marks: networks and the web
- 12 board marks: Matplotlib plots
- Every statement with its exact output
- Common traps, corrected
- Final test with answers
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Accountancy
Partnership Accounts: 36 of 80 theory marks
- 65 board marks: Admission of a Partner
- 26 board marks: Dissolution
- 22 board marks: Retirement/Death
- Goodwill formulas with the book's figures
- 12 common traps, corrected
- 12-question final test with answers
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Biotechnology
Beyond NCERT: 46 of 140 board marks
- 40 marks: Unit V, rDNA and genomes
- 30 marks: Unit VI, culture and bioprocess
- 10 syllabus chapters: every vector, enzyme
- PCR, blots and DNA fingerprinting
- Every number tied to its book page
- Final test with answers
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Accountancy
All 18 ratios, with the book's answers
- 15 marks in every 2025 set: share capital
- 9 marks in every 2025 set: debentures
- 6-mark cash flow in every paper
- 5 marks in every 2025 set: ratios
- 6-mark journal: forfeiture and reissue
- Final test with answers
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सृजनात्मक लेखन और अनुवाद
सृजन 2: all 4 units, Hindi + English parts
- Elements of a poem and a story, Unit 1
- Feature and article writing, Unit 2
- Radio and TV script rules, with marks
- Steps and types of translation, Unit 3
- Levels of editing, Unit 4
- Final test with answers
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Business Studies
Directing: 37 marks in 4 papers, the most
- 8 chapters ranked by what the board asked
- 31 marks: Organising, a 6-marker every set
- 30 marks in 4 papers: nature of management
- 14 principles of Fayol
- Case cues the board keeps using
- Final test with answers
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हिंदुस्तानी संगीत (तबला / पखावज)
Taal notation: 20 of 60 board marks
- 16 of 60 board marks: taal comparison
- 12 of 60 board marks: gharanas
- 13 thekas, from thah to chaugun
- 6 marks: history of the tabla, Unit 3
- 4 biographies, with dates
- Final test with answers
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Business Studies
Financial Markets: 26 marks, not in NCERT
- 15 marks each: Units 9–10 and 11–12
- 4 Ps of marketing, Unit 11
- Consumer Protection Act 2019 tiers, appeals
- Capital structure with EBIT-EPS examples
- The three financial decisions, every factor
- 12-question board-style test
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Economics
Macro marks by unit: Ch 4 leads with 12
- 10 marks: National Income Accounting
- 3 methods for GDP, with identities
- M1–M4 and credit creation, Ch 3
- Every deficit measure of the budget, Ch 5
- 6 chapters: every formula, board numerical
- 12-question final test with answers
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Economics
TrendingUnit 7 (Ch 4–7) carries 20 marks
- 12 marks: Unit 6, Ch 1–3
- 8 marks: Unit 8, India-China-Pakistan
- Every committee, policy and date, by chapter
- Data tables with the book's own numbers
- Common traps, corrected
- 12-question final test with answers
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History
Kings, Farmers and Towns: 35 of 100 marks
- 23 of 100 marks: Thinkers, Beliefs, Buildings
- 22 of 100 board marks: Harappa
- 20 of 100 marks: Kinship, Caste and Class
- 8-mark answer: Theme 2 in 3 of 4 papers
- 5 marks: the Part I map list
- Final test with answers
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History
Travellers, Bhakti-Sufi: 26 of 100 each
- 24 of 100 board marks: Vijayanagara
- 24 of 100 marks: Mughal village, Theme 8
- Q24 from Vijayanagara in every 2025 set
- 3 of 4 papers: source question on travellers
- 5 marks: the two map lists
- Final test with answers
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History
Themes 9–12: 25 theory marks, 1793 to 1950
- 1857 and National Movement map items
- Constituent Assembly committees table
- Gandhiji 1915–1931: Champaran to Salt March
- Permanent Settlement and the Fifth Report
- Bombay Deccan: ryotwari and the 1875 riots
- 12 questions with answers
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Geography
Human Development: 18 of 120 marks asked
- 17 of 120 marks each: industry, services
- 15 of 120 marks: Primary Activities
- 14 of 120 marks: Transport
- 5 marks: world map work
- HDI, rail and internet data as charts
- Final test with answers
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Geography
All 48 CBSE India map items, by chapter
- 20 board marks in 4 papers: Population
- 14 board marks: Minerals and Energy
- 13 of the 28 map items asked: minerals
- 10 marks: Unit III, Ch 3–6
- Common traps, corrected
- Final test with answers
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Geography
30 practical marks: where each one sits
- 18 marks: Ch 1–3, data and diagrams
- 7 marks: GIS, Ch 4
- 5 marks: file and viva
- Mean, median and mode, fully worked
- Which diagram for which data
- 12-question final test with answers
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English Elective · Kaleidoscope
All 16 texts + what the sample paper asked
- 22 textbook marks: how each is asked
- 3 stories: 10 marks in the sample paper
- 9 poems side by side, with devices
- 5 essays, each argument set out
- 6-mark drama extract: Chandalika
- 12-question final test with answers
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Political Science
End of Bipolarity: asked in all 4 papers
- 6-marker in 3 of 4 papers: Security
- 4-marker in all 4 papers: Environment
- 6-marker in 3 of 4 papers: centres of power
- 2 papers asked UN cartoons
- 7 chapters: dates, treaties, leaders
- Final test with answers
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Political Science
40 theory marks, split chapter by chapter
- 8 marks: Chapter 8, 1989 to 2019
- 6 marks each: Chapters 1, 4 and 7
- State-formation and war timelines
- Party tables and election results
- Map clues the board uses
- Final test with answers
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Sociology
Ch 2, 3, 5, 6: the four examined chapters
- 10 marks for each of the four chapters
- Demography formulas for Ch 2
- Sex-ratio and age tables from the book
- 10 must-know facts with a self-check
- Common traps, corrected
- Final test with answers
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Sociology
Five examined chapters, 2025 Qs mapped
- 10 marks each: Units 11, 12 and 15
- 5 marks each: Units 8 and 9
- 4 processes of cultural change, in a table
- Land reforms table, Chapter 4
- Types of social movements, in one table
- Final test with answers
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Psychology
140 board marks counted, chapter by chapter
- 26 board marks each: Ch 1 and Ch 2
- 22 of 140 board marks: disorders, Ch 4
- 20 of 140 board marks: therapies, Ch 5
- 6-mark questions on Freud, RET and Beck
- IQ bands and twin correlations from the book
- Final test with answers
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English Core · Flamingo
All 13 Flamingo texts, with what 2025 asked
- 5 poems: Q7 is always one of these
- 4 writing formats, 18 marks
- 8 prose pieces: events, characters, themes
- Poetic devices with short quotes
- Common traps, corrected
- 12-question final test with answers
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English Core · Vistas
13 Vistas marks + 22 unseen-passage marks
- 12 marks: unseen passage Q1, decoded
- 10 marks: case-based passage Q2, decoded
- Every character, with evidence and quotes
- 7 texts: plot timelines for each
- 4-, 2- and 5-mark answers: how to write
- 12-question final test with answers
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Home Science
Unit II nutrition and food: 23 marks
- 38 of the 70 theory marks: Ch 1–7
- 10 marks: Unit III, ECCE to elderly
- 5 marks: Unit I, work and careers
- 2025 paper and SQP: ranked by what they asked
- Book's tables and figures, charted
- 12-question final test with answers
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Home Science
Ch 8–13: 32 of the 70 theory marks
- 17 marks: Unit IV Fabric and Apparel
- 10 marks: Unit V Resource Management
- 2025 board questions mapped to each chapter
- Every consumer right and standard mark
- Common traps, corrected
- Final test with answers
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Summary
This chapter introduces genetics through Mendel's experiments on the garden pea, establishing the principles of inheritance. Mendel's monohybrid crosses gave the Law of Dominance and the Law of Segregation, while dihybrid crosses gave the Law of Independent Assortment, expressed through phenotypic ratios such as 3:1 and 9:3:3:1. Deviations from Mendelian ratios are explained by incomplete dominance (Snapdragon), co-dominance (ABO blood groups), multiple allelism, pleiotropy and polygenic inheritance (human skin colour). The chromosomal theory of inheritance, proposed by Sutton and Boveri, links genes to chromosomes, supported by Morgan's work on Drosophila showing linkage and recombination, and the construction of genetic maps. Sex determination mechanisms (XX-XY, XX-XO, ZZ-ZW) and the chromosomal basis of sex are explained, along with the role of environment. Mutations, sudden heritable changes in DNA, and the resulting variations are described, including chromosomal aberrations (deletion, duplication) and point mutations like in sickle-cell anaemia. The chapter concludes with the genetic basis of human disorders, classifying them as Mendelian (haemophilia, colour blindness, thalassaemia, sickle-cell anaemia, phenylketonuria) and chromosomal (Down's syndrome, Klinefelter's syndrome, Turner's syndrome).
Mendel's laws of inheritanceDeviations: incomplete dominance and co-dominanceChromosomal theory and linkageSex determinationMutation and variationGenetic disorders in humans
Key terms
Law of Segregation
Mendel's principle that the two alleles of a gene separate during gamete formation so that each gamete carries only one allele.
Incomplete dominance
A pattern where the heterozygote shows a phenotype intermediate between the two homozygotes, as in pink-flowered snapdragon.
Co-dominance
A pattern where both alleles express themselves fully and independently in the heterozygote, as in AB blood group.
Linkage
The tendency of genes located close together on the same chromosome to be inherited together.
Pleiotropy
A condition where a single gene affects multiple, apparently unrelated phenotypic traits.
Aneuploidy
Gain or loss of one or more chromosomes due to failure of segregation (non-disjunction), as in Down's syndrome (trisomy 21).
Extra questions & answers
Try one from this chapter
The phenotypic ratio of a typical dihybrid cross in F2 is: