Class 10 Science Chapter 1: Heredity and Evolution Notes — Maharashtra Board

🧬 1. Introduction to Heredity

Heredity is the transfer of characteristics from parents to their offspring through genes. These traits are passed via DNA, the molecule that carries genetic information inside chromosomes.

Key Concepts:

• Gene: A section of DNA that determines a specific trait.
• Allele: Variants of a gene found at the same locus on a chromosome.
• Genotype: The genetic composition of an individual.
• Phenotype: Observable traits of an individual.

🌱 2. Mendel’s Laws of Inheritance

Gregor Mendel conducted experiments on pea plants and formulated the basic principles of heredity.

Law of Dominance:

Out of a pair of alleles, one may mask the expression of the other (dominant vs. recessive).

Law of Segregation:

Alleles segregate during gamete formation and each gamete receives only one allele.

Law of Independent Assortment:

Alleles of different genes assort independently during gamete formation.

Monohybrid and Dihybrid Crosses:

• Monohybrid Cross: Involves one trait. Phenotypic ratio = 3:1
• Dihybrid Cross: Involves two traits. Phenotypic ratio = 9:3:3:1

🔬 3. Chromosomes, DNA, and Genes

• DNA: A molecule carrying genetic instructions.
• Chromosomes: Thread-like structures made of DNA and proteins.
• Humans have 23 pairs (46 total) of chromosomes.

🦕 4. Evolution

Evolution is the gradual change in living organisms over generations, resulting in the formation of new species.

Theories of Evolution:

• Lamarckism: Proposed inheritance of acquired traits (disproved).
• Darwinism: Explained evolution through natural selection.

Evidence Supporting Evolution:

• Fossil records
• Homologous and analogous organs
• Embryological evidence

Speciation:

Formation of a new species through reproductive isolation and genetic divergence.

📄 Summary 

This chapter introduces the concepts of heredity and evolution. Heredity refers to the passing of traits from parents to offspring through genes located on chromosomes. Mendel’s experiments on pea plants led to three major laws explaining inheritance patterns: dominance, segregation, and independent assortment. DNA, the genetic material, encodes information that defines genotype and phenotype. Evolution is the process by which species gradually change over generations. Charles Darwin’s theory of natural selection explains how organisms better suited to their environment are more likely to survive and reproduce. Evolutionary evidence includes fossils, anatomical similarities, and embryonic development patterns. The process of speciation explains how new species arise due to isolation and genetic changes. Understanding heredity and evolution helps in explaining biodiversity and the unity of life across generations.

📚 Previously Asked Board Questions

1 Mark Questions

• Define heredity.
• Name the scientist known as the father of genetics.

2 Mark Questions

• State Mendel's Law of Segregation.
• What is meant by speciation?

3 Mark Questions

• Differentiate between homologous and analogous organs.
• Explain Darwin’s theory of natural selection.

4 Mark Questions

• Describe Mendel’s experiments and state his laws of inheritance.
• Explain evolution with the help of fossil evidence.

📘 Frequently Asked Questions (FAQs)