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Principles of Inheritance and Variation

Punjab Board · Class 12 · Biology

Complete topic list for Principles of Inheritance and Variation in Punjab Board Class 12 Biology. Key concepts, sub-topics, and what to focus on for board exams.

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

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

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 Chapter Overview – Principles of Inheritance and Variation, Mendel's experimental methodology: Sequential steps from plant selection through statistical analysis to formulate laws of inheritance, Monohybrid cross showing parental cross through F1 and F2 generations with both genotypic and phenotypic outcomes. These are the concepts Punjab Board Class 12 examiners draw on most — study them first, then practise related questions.
How to score full marks in Principles of Inheritance and Variation — Punjab Board Class 12 Biology?
Understand the core concepts first, then work through the 42 practice questions available for this chapter. Revise formulas and definitions regularly, and use flashcards for quick recall before the exam.

Sources & Official References

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

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