An Introduction to Genetic Science
by Arjun Sikand MSc
‘Change is the only constant’, - so the saying goes. Nowhere is this truer than within the realms of bio-analytical science... it’s quite remarkable to see how much things can, and do, change. In the 50 or so years since the structure of DNA was revealed, mankind has progressed by leaps and bounds in developing new applications, from DNA fingerprint profiling and Dolly the cloned sheep, to personalised drug development based on the genetic make-up of an individual.
These discoveries are not restricted just to academia or medicine but are now transferring across a range of industries, with a significant increase in the commercialisation of DNA fingerprint profiling within the legal services community. The last decade in particular has highlighted the power of DNA profiling as an indispensable tool for human identity and relationship testing.
What is DNA?
In essence, DNA is the biological molecule responsible for making you you. It acts as a memory chip, as it were, storing all the information required to build living organisms, from plants and flowers to dogs and humans.
DNA is a complex biological molecule consisting of 2 intertwined strands, forming a double helix. Each of the strands is made up of four major individual components called nucleotides. These nucleotides – adenine, thymine, cytosine, and guanine are enough to encode all the genetic information of an individual, and it is the order in which the different nucleotides are arranged that determines the function of the genes.
On average, human DNA contains 3.5 billion nucleotides, encoding an estimated 30,000 genes in every cell. There are approximately 100 trillion cells in the human body each containing DNA. This means that if you were to unravel your entire DNA and line it up, it would be enough to reach from the earth to the sun and back about 70 times over.
Development of Genetic Theory
Throughout history people have been intrigued by the mechanism of inheritance. From as early as 400BC Hippocrates speculated that "seeds" were produced by various body parts and transmitted to offspring at the time of conception. Across millennia various theories sprang up and died down, but it really wasn’t until the 19th century that a consistent theory began to form. In 1865 Gregor Mendel hypothesised that the phenomenon of the inheritance of certain characteristics is due to transferable elements – the gene. Hence, we have Genetics as the study of Inheritance. In 1869, independently of Mendel but unknowingly in a field related to his work, a Swiss biochemist Friedrich Miescher was the first to isolate nucleic acids, the molecular substrates of the genetic code. As time went on more, people contributed to our understanding of DNA and inheritance. However, the next major breakthrough came in 1953, when James Watson and Francis Crick discovered the structure of DNA and were able to demonstrate how genetic information encoded in DNA could be passed on from generation to generation. Watson and Crick showed that the DNA molecule is a double helix, which consists of two intertwined DNA strands.
The culmination of these works led to what we know of the structure of DNA and the mechanism of its action. But even after knowing the structure, it wasn’t until the mid 1980’s that the power of DNA analysis for identification purposes was revealed.
In 1984 Leicester university professor Alec Jeffreys developed a technique which was to revolutionise both human identity and relationship testing - The DNA Fingerprint.
As with conventional fingerprints, where various loops and ridges are compared between individuals, DNA testing relies on comparing certain DNA features called DNA markers, between two (or more) DNA samples, and studying similarities between them.
The very first case that utilised DNA fingerprinting was Sarba vs. the Home Office, 1985, an immigration case where it was necessary to prove the direct biological relationship between Christianna Sarba and her son Andrew. By comparing Christianna’s DNA sample against that of Andrew’s and his three legally recognised siblings, a direct biological relationship was shown beyond a doubt.
The power of this analytical technique was again demonstrated the following year, when it was used in the Enderby Murder investigations, 1986. Biological samples left on the victim and at the crime scene were collected and analysed, and then compared with the sample provided by the suspect, a man that had allegedly confessed, however the samples didn’t match. This sparked the first DNA man-hunt, and after comparing nearly 2,000 samples the perpetrator, a man called Colin Pitchfork, was found and convicted. So in this case DNA evidence not only helped to incarcerate the criminal, but it also exonerated an innocent man.
And the science continues to evolve. Today we can not only identify an individual by a single cell, but also obtain information from DNA testing about their sex, ethnic background, medical history, and even establish complex relationships such as grandparentage, cousinship and ancestry. Within the next couple of years it may be possible to tell an individual’s age, and who knows what lies beyond?
