Structure: The Human Genome

The human genome contains about 20,000–25,000 pairs of genes. In 1990, an international research programme called the Human Genome Project was set up to identify each gene, its function, and its sequence of nucleotides (the building blocks of DNA); it was completed in 2003. The information gained from this project is being used to understand how genes are controlled and how they contribute to health and disease. Many genes for specific disorders have already been identified.

The X chromosome

Chromosomes can be stained, producing dark and light bands. This image shows the banding pattern and positions of some genes for disorders on the X chromosome.

From the 2010 revision of the Complete Home Medical Guide © Dorling Kindersley Limited.

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