Class 10 | Science | Chapter 08 | Heredity and Evolution

on

🎯Here are exam-focused notes + topic-wise previous year questions (PYQs) & NCERT exercise solution -

🔷 Part 1: Heredity

✅ What is Heredity?

  • Transmission of traits (characters) from parents to offspring.
  • Study of heredity and variations is called Genetics.

✅ Mendel’s Experiments

  • Conducted on pea plant (Pisum sativum).
  • Discovered the basic principles of heredity.
  • Contrasting traits: tall/dwarf, round/wrinkled, yellow/green.

Mendel’s Laws:

Law

Statement

Law of Dominance

One factor dominates over the other.

Law of Segregation

Factors separate during gamete formation.

Law of Independent Assortment

Genes for different traits assort independently.

✅ Important Definitions:

Term

Meaning

Gene

Unit of heredity.

Allele

Alternate form of a gene.

Phenotype

Observable character (e.g., tall).

Genotype

Genetic constitution (e.g., TT, Tt).

Homozygous

Same alleles (TT, tt).

Heterozygous

Different alleles (Tt).

✅ Sex Determination in Humans

  • Humans have 23 pairs of chromosomes:
    • 22 pairs autosomes.
    • 1 pair sex chromosomes.
    • Female: XX
    • Male: XY (sperm determines the sex).

✅ Variation

  • Inherited: Passed to next generation.
  • Acquired: Not passed (e.g., pierced ear).

🔷 Part 2: Evolution

✅ What is Evolution?

  • Gradual changes in organisms over generations.

✅ Charles Darwin’s Theory of Natural Selection

  • Organisms with favorable variations survive and reproduce.

✅ Evidence of Evolution

  • Fossils (remains of organisms).
  • Homologous organs (same structure, different function — e.g., forelimbs of frog, bird, human).
  • Analogous organs (different structure, same function — e.g., wings of bat and bird).

✅ Speciation

  • Formation of new species from existing ones due to:
    • Genetic drift
    • Natural selection
    • Geographical isolation

✅ Human Evolution

  • Modern humans (Homo sapiens) evolved in Africa.
  • Fossil records and tools suggest gradual development of intelligence and upright posture.


📄 Previous Year Questions (PYQs)

🌟 Very Short Answer (1–2 Marks)

✅ Define heredity.

✅ Who is known as the father of genetics?

✅ What is phenotype?

✅ Name the sex chromosomes in humans.

✅ What is a gene?

✅ Give one example of homologous organs.

✅ What are fossils?

🌟 Short Answer (3 Marks)

✅ State Mendel’s law of segregation.

✅ Explain how sex is determined in humans.

✅ Differentiate between homologous and analogous organs with examples.

✅ How do fossils support the theory of evolution?

✅ Write two differences between acquired and inherited traits.

🌟 Long Answer (5 Marks)

✅ Describe Mendel’s monohybrid experiment with a cross and explain his observations.

✅ Explain Darwin’s theory of natural selection.

✅ Describe how geographical isolation can lead to speciation.

✅ Discuss evolution of humans with evidence.


📌 Tips for Exams:

✅ Practice Mendel’s cross with Punnett square.

✅ Learn diagrams:

  • Sex determination in humans.
  • Fossil layers.

✅ Revise definitions and differences (e.g., homologous vs analogous).

✅ Remember examples:

     Fossils: Archaeopteryx
     Homologous: forelimbs
     Analogous: wings of bat & insect.

YouTube | Facebook | Instagram | Linkedin | Whatsapp