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The genome is the complete set of DNA in a living organism. It includes genes that code for proteins, as well as non-coding regions such as introns and pseudogenes, which do not directly produce proteins but still play important roles in regulation and structure (Alberts et al., 2015). Every species has its own unique genome. For example, humans and chimpanzees share about 99% of their DNA, yet the remaining 1% creates significant differences in appearance, behaviour, and abilities (Griffiths et al., 2019).

A useful way to understand the genome is to think of it as a blueprint for a house. The blueprint explains how the house should be built—its size, structure, and materials. In living organisms, the “building materials” are proteins, lipids (fats), and sugars. The genome determines which proteins are produced, which versions of genes (alleles) are used, and how much of each protein is made. This process is called gene expression (Strachan & Read, 2018).
However, genes do not work alone. The environment also strongly influences how an organism develops. For example, genes may provide the instructions for muscle growth, but muscles become stronger only with proper nutrition and physical activity. This interaction between genes and the environment explains why individuals with similar DNA can still develop different traits (Alberts et al., 2015).

Although every cell in the human body contains the same DNA, different cells use different genes. Skin cells and muscle cells, for instance, produce different proteins in different amounts. This selective gene activity shapes physical traits such as eye colour, hair colour, height, and body structure (Griffiths et al., 2019).

Because traits depend on DNA, any change in the genome can affect an organism. A mutation is a change in the DNA sequence that can occur randomly or be caused by environmental factors such as radiation or chemicals. Mutations can happen within genes or in non-coding regions of DNA. While some mutations have no visible effect, others can influence traits, health, or survival (National Human Genome Research Institute, 2023).