Hair samples are used in DNA testing and forensic analysis. DNA is extracted from the hair for the purpose of parental DNA testing and criminal investigations. Let us dig down deeper as to why hair is one of the parameters for checking DNA.
Hair has two parts – shaft and follicle. The shaft is the one you see above the surface of the skin. The follicle or hair root is underneath the skin surface. In the hair, there is keratin, a special type of protein. The same protein is found on the nails, skin, and animal hoofs. (1, 2, and 3)
Image 1: The hair and the different layers.
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Layers of the hair
- Medulla – It is the innermost layer. It consists of soft structures of rounded cells.
- Cortex – It is the middle part of the hair, which contains the pigment that gives the hair its color and elasticity.
- Hair cuticle – It is the scaly layer, which is hard and transparent that serves as a protective covering of the inner parts of the hair. It is also the one responsible for giving the hair its lustrous sheen. (2, 3, and 4)
Image 2: Hair is used in DNA testing and forensic analysis.
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DNA distribution in hair samples
Can you get DNA from hair? Is DNA always available in a hair sample? The hair fiber has keratinocytes; a type of skin cells responsible for keratin synthesis. They naturally die and undergo a process of cornification – the conversion of cells to tough materials like hairs.
During cornification, the cell nucleus gets destroyed and degraded including the genetic materials enclosed within. Therefore, the part of the hair that protrudes out of the scalp (hair shaft) does not have a nuclear DNA.
On the flip side, nuclear DNA can be extracted from the hair root. Can you get DNA from hair? The answer is a big YES! Is DNA always available in a hair sample? The answer is no! (4, 5)
Who performs hair DNA testing?
Hair DNA testing is carried out to check for paternity and forensic investigation. In a forensic laboratory, the governing bodies have their way of extracting the DNA successfully in a given hair sample. They have the best testing techniques and resources.
Usually, in a crime scene, the hair sample does not have the roots attached to it. What the testing personnel does is perform extensive and thorough DNA analysis to check for DNA despite the very low chances of success.
For paternity testing, hair is used provided the hairs have roots attached. Without the roots attached the chances of success are low. Identifying the hair follicle can be done under close observation of the hair using the naked eye. The root of the hair or follicle is a gray-white tiny ball at the tip of the hair shaft. (5, 6, and 7)
Can you perform a DNA test in a hair sample with no follicle?
When performing a hair DNA test for the purpose of paternity, it is a must to have a complete hair sample – with hair shaft and hair follicle. On the other hand, if the purpose of hair DNA testing is for forensic use, a cut hair sample even with no follicle can still be of use. However, a complex procedure has to be made.
The hair needs to undergo a specific test called the MtDNA test or Mitochondrial DNA test. The MtDNA test is a parameter used to find out if two people share the same maternal line. (2, 5, and 7)
Image 3: Hair samples should be collected properly to keep the DNA intact which makes testing pretty easy.
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Collecting a hair DNA sample?
The first thing you should do is to make sure you have a solid hair sample. If you have ripped or plucked from the scalp, then you can immediately send the hair sample to the DNA hair testing facility. A minimum of five hairs is required.
It is a must to use a freshly plucked hair sample. If the hair is old, an advanced testing method is required at an additional cost. Put the hair sample in a dry paper envelope ensuring you do not touch the hair with your bare hands.
Nuclear DNA Vs Mitochondrial DNA testing
A thorough analysis of nuclear DNA has to be made for proper genetic identification and profiling. An electron microscope is used to check for the hair’s nuclear content as it is the only way to visualize the small fragments of DNA due to partial breakdown during the process of cornification.
Another way to test DNA in hair samples is through mitochondrial DNA. it is found in the cell’s mitochondria, which is a type of cell organelle found in the cytoplasm. Its function is to supply the cell with energy. The mitochondrial DNA is more abundant than nuclear DNA. in a human cell, there are thousands of copies of MtDNA. It is a huge difference in number considering that there is only a single copy of nuclear DNA.
The government of some countries has access to DNA databases. It is where the profiles of prosecuted criminals are stored. However, the database profile contains nuclear DNA, which increases its power and usability in solving crimes.
More so, mitochondrial DNA cannot differentiate individuals as people share a common maternal blood line will also share the same mitochondrial DNA profile. So, if the two persons are of the same maternal line, you cannot distinguish which one of them is responsible for a particular crime. So, this explains why forensics prefer to use nuclear DNA over mitochondrial DNA. (7, 8, and 9)
What is the success rate of using hair samples for DNA identification?
There are various factors that can significantly affect the success rate of DNA identification using hair samples. Some of them include the following:
- Dye – the cuticle of the hair can be altered by chemical treatments such as when a dye is used. Dyes can penetrate the spaces between the scaly cells that form the hair cuticle. Hair dye usually contains peroxides which can contribute to the degradation of DNA in the hair. What peroxides do is they break the phosphodiester bonds in DNA.
- Exposure of hair samples to water – Washing of the hair sample can greatly affect the integrity of DNA. it can easily be washed out of the hair fiber. So, the more the hair sample is exposed to water the more DNA is lost. The loss of DNA is because of the degradation and break down of phosphodiester bonds in DNA as well as the damage incurred by frequent washing of the hair.
- Other factors that could affect the success of DNA identification in a hair sample include the age of the sample, the manner the sample was collected, storage, and other external factors such as exposure to chemicals like soaps and cleaning agents and temperature extreme. (1, 5, 9, and 10)
What can hair be used to determine?
Hair analysis is not only intended for DNA identification. It is also used to detect the use of illegal drugs, the presence of heavy metals in the body, and to check for nutritional deficiencies. The presence of hair can also be linked to a suspect or victim in a crime scene primarily because the hair can be moved from one location to another. It is said that about 100 head hairs are naturally shed per person every day.
Hair analysis also helps determine whether the hair is being studied is from humans or animals. If it is from an animal, the examiner can check the species from which it originated. If the hair sample is from a human, the examiner can check as to where particular body parts the hair came from. The examiner will check the hair for:
- Appearance of the medulla
In a forensic examination, the majority of the hair being examined originated either from the head or pubic areas. Hair analysis can also help in differentiating racial groups – Asian ancestry, European ancestry, and African ancestry. (2, 5, and 8)
- European ancestry – The hair is typically straight or wavy with fine to medium-sized pigment granules.
- Asian ancestry – The hair is straight and with medium-sized pigment granules. The cuticle is thicker when compared to the hair of other races.
- African ancestry – They have kinky to curly hair with oval-cross section. They also have large pigment granules.
The hair plays a vital role in determining DNA, which helps in paternity identification and forensic investigation. Examining bodies use various hair examining methods to thoroughly check the sample. For DNA identification and forensic purpose, it is a must to use the most ideal hair sample – the one with the roots attached to the hair.
In the case of hair DNA identification, it is easy to secure a solid hair sample. However, in forensic cases, the integrity of the hair sample is not always guaranteed. Which is why forensic experts use a more advanced hair analysis method. (4, 6, 9, and 10)