🧬 Introduction

Heredity is the passing of traits from parents to offspring. Evolution is the gradual change in organisms over generations, leading to the development of new species.

🌱 1. Heredity

Definition: Transmission of traits from one generation to another.

🔹 Mendel’s Experiments

  • Conducted experiments on pea plants

  • Studied inheritance of traits (like tall/short, round/wrinkled seeds)

  • Proposed laws of inheritance

🔹 Key Terms

  • Gene: A unit of inheritance

  • Allele: Different forms of the same gene

  • Dominant trait: Expressed in hybrid (e.g., Tall)

  • Recessive trait: Hidden in hybrid (e.g., Short)

🔹 Mendel’s Laws

  1. Law of Dominance

  2. Law of Segregation

  3. Law of Independent Assortment

🔹 Monohybrid Cross

  • Cross involving one trait (e.g., Tall × Short)

  • F1 generation: All tall

  • F2 generation: 3 tall : 1 short

🔹 Dihybrid Cross

  • Cross involving two traits (e.g., Round-Yellow × Wrinkled-Green)

  • F2 ratio: 9 : 3 : 3 : 1

🧬 2. Sex Determination

In humans:

  • Females: XX chromosomes

  • Males: XY chromosomes

  • Sex of the child depends on the male gamete

🔄 3. Evolution

Definition: Gradual change in inherited traits of a species over generations.

🔹 Evolutionary Relationships

  • Traced using fossils, anatomical features, and DNA studies

🔹 Fossils

  • Preserved remains of ancient organisms

  • Older fossils found in deeper layers

  • Provide evidence of past life forms

🔹 Homologous Organs

  • Same structure, different function (e.g., forelimbs of humans and birds)

🔹 Analogous Organs

  • Different structure, same function (e.g., wings of insects and birds)

🔹 Speciation

  • Formation of new species due to:

    • Genetic drift

    • Natural selection

    • Geographical isolation

🔬 4. Human Evolution

  • Traced using fossils, tools, and DNA

  • Modern humans (Homo sapiens) evolved in Africa

  • Migration led to human diversity

✅ Key Points to Remember

  • Traits are inherited through genes

  • Mendel explained the pattern of inheritance using pea plants

  • Sex is determined by chromosomes

  • Evolution is supStay Tuned for Chapter 7 Notes!r al evidence

  • Speciation leads to biodiversity over time