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Principles of Inheritance and Variation

Tamil Nadu Board · Class 12 · Zoology

Quick revision notes for Principles of Inheritance and Variation — Tamil Nadu Board Class 12 Zoology. Key concepts, formulas, and definitions for last-minute revision.

44 questions24 flashcards5 concepts

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Key Topics to Revise

1

4.1 Multiple Alleles

  • A gene can exist in multiple forms called alleles
  • When three or more alleles of a gene occupy the same locus on homologous chromosomes, it is called multiple alleles
  • Inheritance involving multiple alleles is called multiple allelism
2

4.2 Human Blood Groups - ABO System

  • Blood group inheritance is a classic example of multiple allelism in humans
  • Karl Landsteiner discovered antigens A and B on red blood cell surfaces
  • Three alleles control ABO blood groups: I^A, I^B, and I^O
3

4.3 Genetic Control of Rh Factor

  • Rh factor (Rh antigen/D antigen) discovered in 1940 in rhesus monkey blood
  • Present on red blood cell surfaces like ABO antigens
  • Individuals with D antigen are Rh positive (Rh⁺); those without are Rh negative (Rh⁻)
4

4.3.1 Erythroblastosis Foetalis (Hemolytic Disease of Newborn)

  • Occurs when Rh negative mother carries Rh positive fetus
  • Mother becomes sensitized during pregnancy or childbirth when fetal blood enters maternal circulation
  • Maternal immune system produces anti-D antibodies (IgG type)

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Full Notes

Key Concepts

Multiple alleles occur when a geneThe ABO blood group is determinedThe Rh factor is a DSex determination varies across speciesFemales have two X chromosomes while

Frequently Asked Questions

What are the important topics in Principles of Inheritance and Variation for Tamil Nadu Board Class 12 Zoology?
Key topics in Principles of Inheritance and Variation include Shows how multiple alleles exist in a population but individuals carry only two; demonstrates the relationship between number of alleles and possible genotypes/phenotypes, Illustrates how three alleles at a single locus produce four distinct blood group phenotypes through different enzyme activities, Shows mapping of six possible genotype combinations to four blood type phenotypes. These are the concepts Tamil Nadu 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 — Tamil Nadu Board Class 12 Zoology?
Understand the core concepts first, then work through the 44 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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