Introduction

No two zebras have exactly the same stripe pattern, no two oak trees produce identical leaves, and no two people—except identical twins—have exactly the same genetic makeup. These differences arise because every individual inherits a unique combination of genes.

Genetic variation is the foundation of biodiversity. It makes every population slightly different and provides the raw material for natural selection and evolution. Without genetic variation, species would have little ability to adapt to changing environments, new diseases, or other challenges.

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What Is Genetic Variation?

Genetic variation refers to the differences in DNA and genes between individuals of the same species.

These differences produce variations in characteristics such as:

• Eye colour.
• Hair colour.
• Height.
• Blood group.
• Flower colour.
• Fur pattern.
• Disease resistance.

Because individuals inherit different combinations of genes, every population contains genetic diversity.

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Figure 1. Genetic variation arises because individuals inherit different combinations of genes.

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Genes and Variation

A gene is a section of DNA that contains instructions for making a particular protein or controlling a characteristic.

Most characteristics are influenced by one or more genes.

Different versions of the same gene are called alleles.

For example, a gene controlling flower colour may have alleles for:

• Purple flowers.
• White flowers.

Different combinations of alleles produce variation within a population.

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How Sexual Reproduction Increases Variation

Sexual reproduction combines genetic information from two parents.

Each parent contributes one set of chromosomes through their reproductive cells (gametes).

During fertilisation:

• A sperm cell joins with an egg cell.
• The offspring receives half its genes from each parent.

Because each offspring inherits a different combination of genes, brothers and sisters are genetically similar but not identical.

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Figure 2. Sexual reproduction mixes genetic information from two parents, producing unique offspring.

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Sources of Genetic Variation

Several processes create genetic variation.

1. Independent Assortment

During meiosis, chromosomes are distributed randomly into gametes.

Each gamete receives a different combination of chromosomes.

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2. Crossing Over

During meiosis, matching chromosomes exchange sections of DNA.

This process is called crossing over (or recombination).

It creates new combinations of genes that were not present in either parent.

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3. Random Fertilisation

Any sperm can fertilise any egg.

This random combination produces enormous numbers of possible genetic combinations.

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4. Mutations

Mutations create entirely new genetic variation by changing DNA itself.

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Mutations

A mutation is a change in the DNA sequence of a gene or chromosome.

Mutations may occur because of:

• Mistakes during DNA replication.
• Radiation.
• Certain chemicals.
• Some viruses.

Most mutations are:

• Neutral (no noticeable effect).
• Harmful.
• Occasionally beneficial.

Beneficial mutations may improve survival and reproduction.

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Figure 3. Mutations create new genetic variation by changing DNA.

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Mutations and Evolution

Mutations introduce new alleles into a population.

If a mutation gives an organism an advantage:

• It is more likely to survive.
• It is more likely to reproduce.
• The beneficial allele may become more common over many generations.

Without mutations, no new genetic information would enter a population.

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Why Genetic Variation Is Important

Genetic variation allows populations to:

• Adapt to environmental changes.
• Resist diseases.
• Survive climate changes.
• Respond to new predators.
• Evolve over time.

Populations with greater genetic variation are generally more likely to survive future challenges.

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Figure 4. Genetic variation provides the diversity needed for natural selection and adaptation.

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Genetic Variation and Evolution

Evolution occurs when inherited characteristics change in a population over many generations.

Natural selection acts on genetic variation.

Individuals with beneficial inherited characteristics are more likely to:

• Survive.
• Reproduce.
• Pass their genes to the next generation.

Over time:

• Helpful alleles become more common.
• Populations gradually evolve.

Genetic variation is therefore the raw material for evolution.

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Examples of Genetic Variation

Examples include:

Humans

• Blood groups.
• Eye colour.
• Natural hair colour.
• Height (partly genetic).

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Animals

• Fur colour in rabbits.
• Shell patterns in snails.
• Beak size in birds.
• Stripe patterns in zebras.

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Plants

• Flower colour.
• Leaf shape.
• Fruit size.
• Disease resistance.

Every species shows genetic variation.

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Figure 5. Genetic variation is found in every population of living organisms.

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Why Scientists Study Genetic Variation

Scientists investigate genetic variation to:

• Improve crops.
• Breed healthier livestock.
• Develop medicines.
• Conserve endangered species.
• Study evolution.
• Understand inherited diseases.

Modern genetics has become one of the most important fields in biology.

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Worked Example

Question

List four sources of genetic variation.

Solution

The four major sources are:

• Independent assortment during meiosis.
• Crossing over during meiosis.
• Random fertilisation.
• Mutations.

Together, these processes create the genetic diversity found in populations.

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Real-World Connection

Doctors and scientists monitor genetic variation in viruses such as influenza. As viruses reproduce, mutations can create new strains that spread more easily or avoid existing immunity. Studying these genetic changes helps researchers develop updated vaccines and improve public health responses to disease outbreaks.

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Did You Know?

Although the DNA of any two humans is about 99.9% identical, the remaining 0.1% contains millions of small genetic differences. These tiny variations contribute to differences in appearance, health, and many other inherited characteristics, making every person genetically unique (except for identical twins, who are genetically almost identical).

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Key Terms

Allele – A different version of a gene.

Crossing over (recombination) – The exchange of DNA between matching chromosomes during meiosis, creating new gene combinations.

Gene – A section of DNA that contains instructions for making a protein or controlling a characteristic.

Genetic variation – Differences in DNA and genes between individuals of the same species.

Mutation – A change in the DNA sequence that creates new genetic variation.

Natural selection – The process by which individuals with advantageous inherited characteristics are more likely to survive and reproduce.

Random fertilisation – The random fusion of sperm and egg cells during sexual reproduction.

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Key Takeaways

• Genetic variation refers to differences in genes and DNA between individuals of the same species.
• Genes and different versions called alleles contribute to inherited variation.
• Sexual reproduction increases variation by combining genetic information from two parents.
• The main sources of genetic variation are independent assortment, crossing over, random fertilisation, and mutations.
• Mutations create new genetic information and provide the raw material for evolution.
• Genetic variation is essential because it enables populations to adapt, survive environmental changes, and evolve over time.