๐Ÿงฌ 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.

๐ŸŒฑ 1. Heredity

Definition: Transmission of traits from one generation to another.

๐Ÿ”น Mendel’s Experiments

  • Conducted experiments on pea plants

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

  • Proposed laws of inheritance

๐Ÿ”น 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)

๐Ÿ”น Mendel’s Laws

  1. Law of Dominance

  2. Law of Segregation

  3. Law of Independent Assortment

๐Ÿ”น Monohybrid Cross

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

  • F1 generation: All tall

  • F2 generation: 3 tall : 1 short

๐Ÿ”น Dihybrid Cross

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

  • F2 ratio: 9 : 3 : 3 : 1

๐Ÿงฌ 2. Sex Determination

In humans:

  • Females: XX chromosomes

  • Males: XY chromosomes

  • Sex of the child depends on the male gamete

๐Ÿ”„ 3. Evolution

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

๐Ÿ”น Evolutionary Relationships

  • Traced using fossils, anatomical features, and DNA studies

๐Ÿ”น Fossils

  • Preserved remains of ancient organisms

  • Older fossils found in deeper layers

  • Provide evidence of past life forms

๐Ÿ”น Homologous Organs

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

๐Ÿ”น Analogous Organs

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

๐Ÿ”น Speciation

  • Formation of new species due to:

    • Genetic drift

    • Natural selection

    • Geographical isolation

๐Ÿ”ฌ 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