Class 10:Heredity and Evolution

 🧬 Heredity and Evolution — Class 10 WBBSE

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🌱 What is Heredity?

Heredity is the passing of traits (like eye colour, height, or shape of leaves in plants) from parents to offspring. It explains why we look like our parents but are not exactly identical to them.

This happens because of genes — units of heredity made of DNA, located on chromosomes!

📚 Key Terms You Must Know

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Traits – Characteristics inherited from parents.

Genes – Segments of DNA that control traits.

Alleles – Different forms of a gene (e.g., tall and dwarf alleles for plant height).

Dominant Trait – Trait that appears in the first generation (e.g., tall plant).

Recessive Trait – Trait that is hidden in the first generation but may reappear later.

Variation – Differences between individuals of the same species.

🔍 Mendel’s Experiments and Laws

Gregor Mendel, known as the Father of Genetics, experimented on pea plants and discovered the basic rules of heredity.

Mendel’s Laws:

1. Law of Dominance – In a pair of contrasting traits, only the dominant trait is expressed.

2. Law of Segregation – Two alleles of a trait separate during gamete formation and unite randomly at fertilization.

3. Law of Independent Assortment – Traits are inherited independently of each other (if genes are on different chromosomes).

🌍 What is Evolution?

Evolution is the process by which living organisms change over generations. It explains how simple life forms gave rise to complex ones and why species differ from each other today.

🔑 Key Points in Evolution

Charles Darwin’s Theory of Natural Selection

Organisms produce more offspring than can survive.

Only those with traits suited to the environment survive and reproduce — "Survival of the fittest".

Evidence of Evolution

Fossils – Preserved remains of ancient organisms.

Homologous Organs – Same structure, different functions (e.g., forelimbs of humans, bats, and whales).

Analogous Organs – Different structure, same function (e.g., wings of bats and insects).

Vestigial Organs – Organs with no apparent function (e.g., human appendix).

🔄 Heredity and Evolution Connection

Variations arise through genetic changes.

Natural selection acts on variations.

Over time, beneficial traits spread in a population, leading to evolution.

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📝 Quick Tips for WBBSE Exams

Remember Mendel’s ratios:

Monohybrid cross → 3:1 ratio (phenotype)

Dihybrid cross → 9:3:3:1 ratio (phenotype)

Use examples from real life in your answers (e.g., antibiotic resistance in bacteria as modern evolution).

Draw clear diagrams of crosses and fossils for extra marks.

📌 Final Thought:

Heredity gives the blueprint, evolution rewrites it over time. Both together tell the story of life’s journey on Earth.

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