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The idea

The human genome is the complete set of genetic material in a human cell. Its study has three main applications. First, searching for genes linked to different types of disease: comparing genomes of affected and unaffected people can reveal gene variants associated with conditions such as cancer or heart disease, aiding diagnosis and prevention. Second, understanding and treatment of inherited disorders: identifying the faulty allele behind a disorder such as cystic fibrosis helps explain how it is inherited and supports treatments such as gene therapy. Third, tracing human migration patterns from the past: comparing DNA between populations shows how humans moved around the world over thousands of years.

For example: Mitochondrial DNA and Y-chromosome markers act like inherited tags that track maternal and paternal lineages.

What earns the marks

• The human genome is the entire genetic material of an organism, and studying it allows identification of genes linked to disease.
• Comparing DNA of people with and without a condition can reveal gene variants associated with diseases such as cancer, aiding earlier diagnosis or prevention.
• Identifying the gene responsible for an inherited disorder, such as the allele behind cystic fibrosis, improves understanding of how the disorder is inherited.
• Knowledge of an inherited disorder's genetic cause can support treatment, for example gene therapy or screening programmes.
• Comparing DNA sequences between different human populations provides evidence for migration patterns over thousands of years.
• Mitochondrial DNA and Y-chromosome DNA are useful in migration studies because they are inherited in a traceable way.

Common mistakes and how to put them right

• Thinking the genome is only the genes coding for proteins.

  Put it right: The genome is all the genetic material, including non-coding DNA.

• Confusing tracing migration with tracing disease inheritance.

  Put it right: Migration studies compare DNA between populations, while disease studies compare affected and unaffected individuals.

• Assuming gene identification automatically cures a disorder.

  Put it right: It improves understanding and can inform treatment, but treatments such as gene therapy are still being developed.

Exam tips

• Link each application to a named example, such as cancer for disease genes or cystic fibrosis for inherited disorders.
• Use the phrase 'comparing DNA' when explaining both disease gene searches and migration tracing.
• For migration questions, mention that DNA differences accumulate over time and can indicate how closely populations are related.