DNA is short for deoxyribonucleic acid and is the building block of all life. We each have a unique set of DNA inherited from our parents. No two people (other than identical twins) will share the same set of DNA molecules.
It is a long ladder-like molecule found in every cell of the body and is made up of an alternating sequence of nucleotides (adenine, thymine, cytosine and guanine). Adenine will always pair with thymine and cytosine with guanine. They form a repeating sequence of pairs along the length of the molecule and it is this sequence that is unique to each person.
It is possible for scientists to decipher the pattern of each person’s DNA; a process called gene or whole genome sequencing.
DNA in cancer cells is different; something has damaged them or caused them to change.
Sometimes, DNA molecules change through natural cell processes, sometimes they change through exposure to certain chemicals. The chemicals in tobacco smoke is a good example.
ctDNA refers to the DNA from cancer cells circulating in the blood stream.