You are a unique person
Your chromosomes contain about 24,000 genes, the instructions that made you grow into the person you are. Your genes contain two sets of instructions: you inherited one set from each of your parents. Most of these genes have several versions, called alleles. For example, different alleles of genes for eye colour give rise to brown or blue eyes. Although you share a particular allele with many other people, no one in the world has exactly the same combination of alleles as you - unless you have an identical twin.