What is the difference between DNA, a gene and a chromosome?

All these three things are key words in the section of biology called Genetics. Genetics is what makes each person unique; except for identical twins every single person has a unique genetic code. DNA is the name for the long molecule that is found within the nucleus of every cell in our body. It can be imagined like a long sentence made up of very special letters either A, T, G or C. These letters can be in any order and the whole string of human DNA has 3 billion letters in total. It is the order of these letters that makes each person unique. A gene is a group of these special letters and you can imagine it to be like chapters of a book formed from many 'letters' within the genetic code. In humans a gene 'chapter' can be anywhere from 27000 to 2 million letters long. Each gene contains a code that builds one protein. A chromosome is a group of genes. You can imagine that a chromosome is like a volume in a series of books. Each human chromosome 'volume' is made up of about 20000-25000 gene 'chapters'. Chromosomes are always found in pairs, because DNA is inherited from your parents and one chromosome comes from your Mother and the other from your Father. In every human cell there are 23 pairs of chromosomes.