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Principles of Inheritance and Variation — Syllabus

Punjab Board · Class 12 · Biology

What Principles of Inheritance and Variation covers in Punjab Board Class 12 Biology: 4 topics, for the 2026-27 session.

42 questions31 flashcards5 concepts

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A comparison chart illustrating Mendel's seven pairs of contrasting traits in pea plants, showing both dominant and recessive phenotypes for each trait.
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4 Topics · Punjab Board Class 12 Biology · 2026-27

Topics in Principles of Inheritance and Variation

1

Mendel's Experiments and Laws of Inheritance

  • Mendel worked on Pisum sativum (garden pea) for 7 years (1856–1863) and studied 7 pairs of contrasting traits.
  • He used true-breeding lines – plants that show stable trait inheritance over several generations through continuous self-pollination.
  • The 7 contrasting traits: Stem height (Tall/Dwarf), Flower colour (Violet/White), Flower position (Axial/Terminal), Pod shape (Inflated/Constricted), Pod colour (Green/Yellow), Seed shape (Round/Wrink
2

Inheritance of One Gene – Monohybrid Cross

  • Monohybrid cross: Cross between parents differing in ONE pair of contrasting traits.
  • Example: Tall (TT) × Dwarf (tt) → F1: All Tall (Tt) → F2: 3 Tall : 1 Dwarf.
  • F1 phenotypic ratio: 1 (all Tall) | F2 phenotypic ratio: 3 Tall : 1 Dwarf.
3

Inheritance of Two Genes – Dihybrid Cross and Law of Independent Assortment

  • Dihybrid cross: Cross between parents differing in TWO pairs of contrasting traits.
  • Example: RRYY (Round, Yellow) × rryy (Wrinkled, Green) → F1: All RrYy (Round, Yellow).
  • F1 self-pollination → F2 phenotypic ratio: 9 Round Yellow : 3 Wrinkled Yellow : 3 Round Green : 1 Wrinkled Green = 9:3:3:1.
4

Chromosomal Theory of Inheritance, Linkage and Recombination

  • Chromosomal Theory of Inheritance was proposed by Walter Sutton and Theodore Boveri (1902).
  • They noted that chromosome behaviour during meiosis parallels the behaviour of Mendel's factors (genes).
  • Both chromosomes and genes: (a) occur in pairs, (b) segregate during gamete formation, (c) independent pairs segregate independently.

Key Concepts

Genes are units of inheritance containingWhen two contrasting alleles existDuring gamete formation (meiosis)When two or more gene pairsGenotype refers to the genetic composition

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Frequently Asked Questions

What are the important topics in Principles of Inheritance and Variation for Punjab Board Class 12 Biology?
Key topics in Principles of Inheritance and Variation include Mendel's Experiments and Laws of Inheritance, Inheritance of One Gene – Monohybrid Cross, Inheritance of Two Genes – Dihybrid Cross and Law of Independent Assortment, Chromosomal Theory of Inheritance, Linkage and Recombination. Study these first, then practise questions on each for the Punjab Board Class 12 board exam.
How should I revise Principles of Inheritance and Variation for the Punjab Board Class 12 board exam?
Learn the core ideas first, then work through the 42 practice questions on Principles of Inheritance and Variation. Revise definitions regularly and use flashcards for quick recall before the exam.

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Content is aligned to the official syllabus. Refer to the board website for the latest curriculum.

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