Since we all have a unique genetic finger print, linking criminal to crime is often not too difficult with the right material in hand. However, with twins, things are different. Through twin DNA testing we know that twins may have identical fingerprint. People have probably never thought of whether identical twins who share identical copies of their DNA also share identical fingerprints. The Atlanta Twin murder case which involved Ronald Smith and Donald Smith is interesting to highlight the issue.
What exactly do we mean by identical twins or fraternal twins?
Understanding the process of fertilisation during conception is important to understanding twins. Identical twins are medically referred to as monozygotic. This is because a single sperm cell fertilises a single egg and the egg splits into two at a later stage forming two independent twins. These twins will have identical DNA because they were formed from the same egg and will each have an identical cop of the genetic material in that cell.
Dizygotic twins are conceived when two independent sperm cells fertilise two eggs. Their genetic makeup will be different and although it can bear considerable similarities it can never be an exact copy of the other. Dizygotic twins form around 75% of all twins meaning that monozygotic (identical twins are quite uncommon). Moreover, identical twins are always of the same sex since the genetic material comes from the same single egg and can only encode the genetic information for one gender.
Do Identical Twins have the Same Fingerprints? Atlanta Twin Murder Case
In 2008, Donald Smith was arrested for the murder of Genai Coleman, a county schoolteacher. A DNA saliva test using a cigarette butt that was found in the car used during the attack was used to carry out forensic testing. Forensic DNA evidence showed that the DNA found at the crime scene belonged to Donald; with this incriminating evidence he was arrested. Throughout the legal accusations, Donald consistently declared his innocence. However, there was also some CCTV footage which showed he was at the crime scene and this also dampened his plea of innocence in the eyes of the court.
Donald said that it was his brother that was guilty of the crime and this made all the DNA forensic investigations somewhat redundant as Donald did have an identical twin, Ronald, who shared his exact genetic make-up. Relying on simply the DNA evidence would have proved inconclusive: it could have been either of the twins as their DNA was indistinguishable.
DNA testing evidence put aside and fingerprinting used in favour
DNA testing is highly accurate in such investigations. The chances of two people having the same DNA are minute; in fact, chances are 10 billion to 1. It is only with identical (monozygotic twins) that such problems arise. The police went on to collect fingerprints from the vehicle and found that the fingerprints matched those of Ronald and thus, Donald was luckily freed from all accusations.
Are our fingerprints not linked to our DNA?
Our fingerprints are not encoded in our genetic make-up or at least not entirely. In fact, identical twins will not share the same fingerprints. In terms of the nature and nurture debate, our fingerprints are a physical characteristic that depends on environmental conditions too. We being to develop our fingerprints while in the uterus and both our genetic make-up and the environment around us will determine the phenotype.
Nutrition while in the womb, perhaps the type of nutrition, the formation of the fingers in the first trimester and the position of the foetus in the womb are all believed to contribute to the shape of our fingerprints. Identical twins will have considerably similar fingerprints since they share the same environment but they will not be the same and there are bound to be variations from one finger to the next.
DNA testing is today highly accurate and reliable. The case involving identical twins such as Ronald Smith and Donald Smith are few and far between. Twin DNA testing was not quite conclusive to this crime case with identical twins, but DNA testing is invaluable to help solve criminal cases.