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Principles of Inheritance and Variation

ICSE · Class 12 · Biology

Quick revision notes for Principles of Inheritance and Variation — ICSE Class 12 Biology. Key concepts, formulas, and definitions for last-minute revision.

130 questions50 flashcards5 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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Key Topics to Revise

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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.

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Full Notes

Key Concepts

Heredity is the transmission of traitsMendel's work on garden pea ledA monohybrid cross involves one pairIncomplete dominance appears when neither alleleCodominance occurs when both alleles express

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 Mendel's Laws — Cross Results, ABO Blood Group Inheritance, Dihybrid Cross — F2 Ratio. These are the concepts ICSE Class 12 examiners draw on most — study them first, then practise related questions.
How to score full marks in Principles of Inheritance and Variation — ICSE Class 12 Biology?
Understand the core concepts first, then work through the 130 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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