Sex Determination
Telangana Open School (TOSS) · Class 12 · Biology
Complete topic list for Sex Determination in Telangana Open School (TOSS) Class 12 Biology. Key concepts, sub-topics, and what to focus on for board exams.
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Topics in Sex Determination
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.
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.
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.
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
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