Intro to genomic testing

What is DNA?

DNA is a chemical that contains our genetic information. It is a long molecule made up of four different chemicals, or bases, represented by the letters A, T, C and G. These bases form long strings which twist around each other to give the characteristic double helix shape.

As well as being helix-shaped, DNA is tightly packed so it takes up less space. If you stretched the DNA in one cell all the way out, it would be about 2 metres long.

The information encoded within DNA contains the instructions for making and maintaining you.

If you are unsure about any of the terms used, please see this A-Z Genomics glossary.

What is a genome?

Your genome is all 3.2 billion letters of your DNA. It contains around 20,000 genes. A gene is made up of a short sequence of DNA which contains a code made up of chemical letters. This code instructs the cell which amino acids to piece together to make a protein. Genes are the instructions for making the different components of our bodies – from the keratin in hair and fingernails to the antibody proteins that fight infection.

Genes make up about 1-5% of your genome. The rest of the DNA, between the genes, is important for controlling the genes. For example, it can switch genes on and off at the right time.

We share over 99% of our genome with other people, but that still leaves more than 3 million differences between us.

Many of these differences in our DNA, known as variants, have no effect, but there are some variants that can affect our health.Many of these differences in our DNA, known as variants, have no impact, but there are some that can affect our health.

What is the difference between genetics and genomics?

Genetics is the study of genes and their roles in inheritance – in other words, the way that certain traits or conditions are passed down in the genes from one generation to the next. In healthcare, genetics has typically focused on variations in a single gene when determining the cause of a health condition.

Genomics is an all-encompassing term that takes into account all the DNA in a person’s or organism’s genome – both the genes that code for proteins and the non-coding regions. It looks at how genes are expressed and the interplay between different genes.