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Principles of Inheritance and Variation — Syllabus

ICSE · Class 12 · Biology

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

130 questions50 flashcards5 formulas & key relations5 concepts

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A detailed diagram illustrating the process of crossing over, where genetic material is exchanged between non-sister chromatids of homologous chromosomes during Pachytene of Prophase I.
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4 Topics · ICSE Class 12 Biology · 2026-27

Topics in Principles of Inheritance and Variation

1

1. Heredity, Variation, and Mendel’s Work

  • Genetics studies heredity and variation.
  • Heredity means transmission of genetically based characters from parents to offspring.
  • Variation means differences among individuals, even within the same family or species.
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2. Mendel’s Laws and Basic Crosses

  • Mendel studied monohybrid and dihybrid crosses.
  • A monohybrid cross involves two plants differing in one character.
  • A dihybrid cross involves two pairs of contrasting characters.
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3. Deviations from Mendelism: Incomplete Dominance, Co-dominance, Pleiotropy, and Multiple Alleles

  • Incomplete dominance means neither allele is completely dominant, so the F1 shows an intermediate phenotype.
  • In incomplete dominance, phenotype and genotype ratios in F2 are the same: 1:2:1.
  • Snapdragon and four O’clock plant show incomplete dominance for flower colour, producing pink F1.
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4. Chromosomal Theory, Linkage, and Crossing Over

  • Sutton and Boveri independently proposed the chromosomal theory of inheritance in 1903.
  • The chromosomal theory states that genes are located on chromosomes and chromosomes segregate and assort during meiosis.
  • Chromosomes occur in pairs like alleles.

Key Concepts

Central concept: Genetics: heredity, variation, inheritance patterns, and chromosomal basis of inheritance

Heredity and variationMendel and his experimentsMendelian lawsBasic genetic termsOther inheritance patternsChromosomal theory of inheritanceLinkage and crossing overSex determination and sex-linked inheritance

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Frequently Asked Questions

What are the important topics in Principles of Inheritance and Variation for ICSE Class 12 Biology?
Key topics in Principles of Inheritance and Variation include Heredity, Variation, and Mendel’s Work, Mendel’s Laws and Basic Crosses, Deviations from Mendelism: Incomplete Dominance, Co-dominance, Pleiotropy, and Multiple Alleles, Chromosomal Theory, Linkage, and Crossing Over. Study these first, then practise questions on each for the ICSE Class 12 board exam.
How should I revise Principles of Inheritance and Variation for the ICSE Class 12 board exam?
Learn the core ideas first, then work through the 130 practice questions on Principles of Inheritance and Variation. Revise 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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