We have learnt that we inherit characteristics like freckles and brown eyes from our parents through genes. For this reason, a gene is often called a hereditary unit. The inherited genes from our parents store the genetic information that dictates the development of our traits. These genes are segments made of molecules known as deoxyribonucleic acid(DNA, for short); one DNA molecule is called a nucleotide. DNA molecules come together forming long chains. Two complementary chains are paired together and form a structure like a spiral stair called the double helix structure. A gene is a section of this structure and the length varies from one gene to another. Each pair of DNA chains is coiled up inside a chromosome together with a type of protein ca ed histone. A single chromosome therefore carries many genes. The physical position of a particular gene on a chromosome is called a locus