Genes, DNA and our health are always in the news. This section will help it all make sense.
We all began life as a single cell. It was your genes that guided that cell to divide in two, and then into four and so on until you developed into a complete human being.
But the role your genes play in shaping who you are doesn’t end at birth.
Your genes are constantly interacting with the environment around you. They influence everything from your health to your appearance, your behaviour and your personality.
Our fun, simple animation will show you What 'Genes' Means »
Chromosomes, genes and DNA
These three elements are within almost every one of the 50 trillion or so cells that our bodies contain.
Cells are made up of different types of proteins depending on what sort of function that cell has - whether the cell is a liver cell, a brain cell, or a skin cell, for example.
Inside almost every one of these cells is a tiny structure called the nucleus which acts like the control centre of the cell. The nucleus carries the instructions for making all the proteins particular to each cell type, written down in the form of DNA.
A male set of chromosomes (karyoptype)Chromosomes
Inside the nucleus of a cell are 46 chromosomes. Each one is made up of a strand of DNA (deoxyribonucleic acid) – an incredibly long molecule which carries the code for all your genetic information.
It's estimated that if a strand of DNA was stretched out, it would be around two meters long, even though the average cell is smaller than a pinhead.
Chromosomes are inherited in pairs: 23 from your mother and 23 from your father. When cells divide the chromosomes pair up which is why they’re often shown as ‘x’-shaped in diagrams like the one on the right.
The relationship between cells, chromosomes and DNA
Photo: Nat. Institute of General Medical Sciences
Genes
The strand of DNA which makes up each of your chromosomes is arranged into sections called genes which are coded instructions for making proteins.
So if you think of a chromosome as a volume of an encyclopaedia, then a gene is a single chapter within that volume, and the words that make up that chapter are the information encoded in your DNA.
Almost every cell in your body (with the exception of red blood, egg and sperm cells) contains a complete set of around 25,000 genes – known as your genome.
But the cell only uses the ones it needs to carry out its role. For example, a heart cell will use different genes to a lung cell.
DNA
DNA (deoxyribonucleic acid) is a very long double-stranded molecule, tightly coiled into a ‘double helix’ shape which looks like a twisted ladder. The ‘rungs’ of the ladder are made up of pairs of interlocking units called nucleotides which are represented by the letters A (adenine), T (thymine), C (cytosine) and G (guanine). ‘A’ always pairs up with ‘T’, and ‘C’ with ‘G’.
These letters spell out three letter ‘words’, called codons, which in turn form sentences, or ‘genes’. So a ‘gene’ is a sequence of nucleotides (ATTCAGCGA etc.) which encodes the instructions for making proteins – the machinery for the body’s chemistry.