The body is made up of tiny building blocks called cells. Each cell has a set of GENES, which control the cell. Think of genes as the words that spell out the instructions for everything a cell does. A kidney cell has the same set of instructions as a brain cell. But each cell only reads the instructions that are relevant to its functioning. The language of these instructions is called DNA.

The genes are ordered very precisely into special packages called CHROMOSOMES –  the chapters. A normal human cell has 46 chromosomes, a set of 23 from each parent, each having its own recognisable pattern. There is a set order to the genes on each chromosome, which has allowed us to put together a standard gene map and DNA sequence for each chromosome (via the Human Genome Project).

The chromosomes only take on their recognisable shape during cell division. All other times the chromosomes are unravelled. The sum of the chromosomes is called the NUCLEUS, and what we normally think of as a nucleus (the most obvious large blob in the middle of the cell) is the INTERPHASE NUCLEUS, where the chromosomes are in this unravelled state.

Cancer is a disease of the genes. Sometimes a misprint slips into the DNA instructions. This is usually ok – cells can tolerate or correct most mistakes. But it’s also the basis of cancer – cells that have escaped the usual set of controls because of the changes to the instruction manual.

A GENOME is all of the DNA (or sometimes a similar molecule called RNA) in an organism – plant, animal, virus, etc.

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