Chapter 8: Heredity and Evolution
Simple, exam-focused CBSE Class 10 Science notes — star topics, concepts, common mistakes, and previous year question patterns, all on one page.
Chapter 8: Heredity and Evolution
⭐ Star Topics / Most Important
- Mendel's laws and monohybrid/dihybrid cross
- Sex determination in humans
- Evidence of evolution
- Speciation
Detailed Chapter Notes
Gregor Mendel's pea plant experiments (tall vs dwarf, round vs wrinkled seeds) laid the foundation of genetics.
Monohybrid cross: tall (TT) x dwarf (tt) → F1 all tall (Tt), since tall is dominant. F1 self-pollinated → F2 shows 3:1 ratio, proving the recessive dwarf trait wasn't lost.
Dihybrid cross (two traits) gives a 9:3:3:1 ratio in F2, showing independent inheritance of traits (Law of Independent Assortment).
Sex determination: humans have 23 chromosome pairs; females are XX, males are XY. Since the mother can only give X, the father's contribution (X or Y) determines the child's sex.
Evolution is gradual change in inherited traits over generations via natural selection, drift, and variation. Homologous organs (same structure, different function — bat wing/human arm, showing common ancestry) vs analogous organs (different structure, same function — bird wing/butterfly wing, convergent evolution).
Speciation is formation of new species, usually via geographical isolation and accumulated variation.
The most repeated mistake: saying "evolution means becoming more advanced" — wrong, it means becoming better adapted to a specific environment, not objectively superior. Also, don't mix up homologous (proves common ancestry) with analogous (does not).
Search on YouTube: Heredity and Evolution Class 10 Mendel experiment explained for a visual walkthrough of this chapter.
- Why is it wrong to say the mother is responsible for determining the sex of a baby? (3 marks, HOTS)
- Explain Mendel's monohybrid cross with a suitable example (3 marks)
- Differentiate between homologous and analogous organs with examples (3 marks)
- What is speciation? Name factors that lead to it (2 marks)
- If trait A exists in 10% of a population and trait B in 60%, which arose earlier? (2 marks, HOTS)