When you read about human genetics, three fundamental concepts you will come across are: the gene, the chromosome and the DNA. When I first encountered the topic, I could mostly understand what each term meant, but I struggled to distinguish them precisely. That was until I came across a fantastic analogy in the book ‘The Selfish Gene’.
I’m recounting below the book’s passage (edited for brevity).
There are about a thousand million million cells making up an average human body, and, with some exceptions which we can ignore, every one of those cells contains a complete copy of that body’s DNA. This DNA can be regarded as a set of instructions for how to make a body, written in the A, T, C, G alphabet of the nucleotides. It is as though, in every room of a gigantic building, there was a book-case containing the architect’s plans for the entire building. The ‘book-case’ in a cell is called the nucleus. The architect’s plans run to 46 volumes in humans—the number is different in other species. The ‘volumes’ are called chromosomes.