Where is DNA found?

DNA is found in almost every cell of the human body, stored mainly in the cell’s nucleus and, to a lesser extent, in structures called mitochondria.

This means DNA can be found in many types of biological samples including blood, saliva, hair, skin cells, and more, making it possible to perform accurate DNA testing using a wide range of sample types.

In this article, we’ll break down exactly what DNA is, where it’s located in human cells, and which body parts or fluids contain DNA that can be used for DNA testing – from at-home DNA tests to forensic investigations.

What is DNA?

Deoxyribonucleic acid or DNA is the instruction manual for life. It’s the unique genetic code found in almost all living organisms, including humans.

DNA contains the instructions needed to build and maintain your body. It determines your physical traits such as eye colour and hair type, and how your body functions.  

DNA is made up of four chemical bases: adenine (A), thymine (T), cytosine (C), and guanine (G). These bases pair up (A with T, C with G) to form a double helix structure. Segments of DNA form genes, which are organised into chromosomes. Almost every human being has 23 pairs of chromosomes, half inherited from each parent.

Because DNA is unique to each individual (except identical twins), it’s used in many types of genetic testing, including paternity testing, ancestry testing, and criminal investigations.

Where is DNA found in human cells?

DNA is stored in two main locations inside human cells:

The nucleus

The nucleus is the control centre of the cell, holding most of the cell’s DNA. This is called nuclear DNA. It is organised into 23 pairs of chromosomes and contains the full genetic instructions for the individual.

Nuclear DNA is the primary source used for most DNA testing, including paternity, maternity and sibling tests.

The mitochondria

Mitochondria are tiny structures in cells that generate energy. They contain a small amount of DNA called mitochondrial DNA (mtDNA).

Unlike nuclear DNA, mitochondrial DNA is inherited only from the mother and is especially useful for tracing maternal ancestry, and in forensic cases involving old or degraded samples.

Where is DNA found in the body?

DNA can be extracted from many different types of biological samples. However, some are more reliable and practical for DNA testing than others.

Here is a comparison of different sample types and their reliability when used for DNA testing:  

Saliva and cheek cells

Saliva contains buccal (cheek) cells, which are rich in DNA. This is why cheek swab sample collection is the most popular and preferred method for home DNA tests. It is non-invasive, simple, and cost-effective.

Blood

DNA is found in white blood cells (not red cells). Blood is a very reliable source of DNA and is often used in clinical and forensic testing. However, for home DNA tests, cheek swabs are most commonly used, highly accurate and easier to collect.  

Nails

Nail clippings can be a good source of DNA, particularly in circumstances where collecting a cheek swab sample is not feasible (i.e. where a relative has passed away or is otherwise unavailable to provide a cheek swab sample for DNA testing).

Bones and teeth

Both are excellent sources of DNA, especially in forensic or archaeological contexts where the body is no longer intact. DNA in bones and teeth is well-protected and can last for years or even centuries.

Semen and other bodily fluids (vaginal fluids, menstrual blood)

Semen, menstrual blood, and vaginal fluids all contain human cells rich in DNA. These are often used in forensic investigations.

Hair

Only hairs with the root attached contain nuclear DNA. Hair shafts without roots do not. Hair may be used in forensic or historical testing but is not recommended for home DNA relationship testing.

Learn more: Can you do a paternity test with hair?

Skin cells

Skin cells contain DNA, but collecting enough of them for testing is difficult. They are sometimes used in forensic cases, especially when found on objects or clothing.

Sweat

Sweat does not contain DNA as it lacks cells. However, skin cells left with sweat on clothes may contain trace DNA.

Faeces

Faeces mostly contain bacteria and food waste, with little human DNA. It is not a viable sample for testing.

Urine

Urine contains few human cells, so it is generally not a reliable source of DNA.

How is DNA collected for testing?

For most home DNA tests, a DNA sample is collected using a cheek (buccal) swab. This process is painless, fast, and provides high-quality DNA for analysis.

In the laboratory, cells from the swab are analysed to extract the DNA. In forensic or medical settings, other sample types may be used based on what is available including blood, hair, or bodily fluids.

Where can I get a DNA test?

If you’re interested in how DNA testing can provide answers about family relationships, health or even your ancestry, AlphaBiolabs offers a wide range of fast, accurate DNA testing services to suit your needs.

Explore our range of DNA testing services or contact our friendly Customer Services team on 01 402 9466 or info@alphabiolabs.ie for more information.