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Sex Determination — Syllabus

Telangana Open School (TOSS) · Class 12 · Biology

What Sex Determination covers in Telangana Open School (TOSS) Class 12 Biology: 4 topics, for the 2026-27 session.

40 questions25 flashcards3 formulas & key relations5 concepts

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4 Topics · Telangana Open School (TOSS) Class 12 Biology · 2026-27

Topics in Sex Determination

1

Types of Chromosomes

  • There are two types of chromosomes: autosomes and allosomes (sex chromosomes).
  • Autosomes control somatic (body) traits and are present in pairs in both males and females.
  • Allosomes determine the sex of an individual and differ between males and females.
2

Chromosomal Theory of Sex Determination

  • Sex is determined by the type of sex chromosomes present in the zygote after fertilization.
  • Two main patterns: male heterogamety (XY system) and female heterogamety (ZW system).
  • In male heterogamety, males produce two types of gametes (X and Y), while females produce only X gametes.
3

Types of Sex Determination Mechanisms

  • XX-XO system: Found in grasshoppers, bugs; males have XO (one X), females have XX.
  • XX-XY system: Found in humans and Drosophila; males XY, females XX.
  • ZO-ZZ system: Found in moths and butterflies; females ZO, males ZZ.
4

Sex Determination in Drosophila – Genic Balance Theory

  • Calvin Bridges proposed the genic balance theory for Drosophila.
  • Sex is determined by the ratio of X chromosomes to sets of autosomes (X/A ratio), called the sex index.
  • If X/A = 1.0 or more → Female; if X/A = 0.5 or less → Male; if between 0.5 and 1.0 → Intersex.

Key Concepts

Central concept: Sex Determination

Chromosomal Theory of Sex DeterminationHaplodiploidyGenic Balance Theory (Drosophila)Hormonal Control of Sex Determination

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Frequently Asked Questions

What are the important topics in Sex Determination for Telangana Open School (TOSS) Class 12 Biology?
Key topics in Sex Determination include Types of Chromosomes, Chromosomal Theory of Sex Determination, Types of Sex Determination Mechanisms, Sex Determination in Drosophila – Genic Balance Theory. Study these first, then practise questions on each for the Telangana Open School (TOSS) Class 12 board exam.
How should I revise Sex Determination for the Telangana Open School (TOSS) Class 12 board exam?
Learn the core ideas first, then work through the 40 practice questions on Sex Determination. 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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All Telangana Open School (TOSS) Class 12 Biology Syllabus

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