Dna Profiling Techniques in Forensic Science

Topics: DNA, DNA profiling, Restriction fragment length polymorphism Pages: 7 (2274 words) Published: February 6, 2013
Literature Review and Project Proposal

Title: DNA Profiling Techniques in Forensic Science


Since 1985, DNA profiling in forensic science has become very important in this virtual era of technology and in the world of science that solves both major and minor crimes. Small traces of DNA are considered in all circumstances from how the DNA was collected to fully obtaining the profile in its significant form. Traces of sweat, blood and semen are the most common type’s evidence found at crime scenes. There are several different methods for creating a DNA profile such as STR (Short Tandem Repeat), PCR (Polymerase Chain Reaction), Y chromosome analysis, Restriction Fragment Length Polymorphism (RFLP) and Mitochondrial DNA (MtDNA) analysis. All these types of methods are able to extract DNA from a chosen sample taken from a crime scene. DNA profiling is the information of how a sample is processed and analysed and a DNA profile must be created by collecting and analysing VNTR’s (Variable Number Tandem Repeats), these are unique sequences on the loci which is an area on chromosomes. Most DNA sequences in different people look too similar to tell apart whereas VNTR result in bands that are unique enough for identification of individuals.

DNA (deoxyribonucleic acid) is the hereditary material in almost all living organisms. In 1953 researchers J. Watson and F. Crick saw the structure of DNA. DNA consists of two long strands that are built up chain like, each consisting four nucleotide subunits, attached to a sugar phosphate backbone. Adenine (A), guanine (G), cytosine (C) and thymine (T) are bases that are arranged pairwise in the middle of the DNA stand. The nucleotides are covalently linked together, from which the bases A and T, G and C bind by a hydrogen bond (Bray et al 2010: 173). Figure 1 shows the order of the bases, which determine the biological information available for building, and maintaining an organism, the sugar phosphate group molecules form the vertical side piece and the base pairs form a ring shape to create a spiral called a double helix. The two backbone chains run in opposite directions, this is specific for base to base bonding which allows this genetic information contained in DNA to be copied accurately from one generation of cells to the next.

Figure 1 – DNA
By Jaspreet (Bray et al 2012)

There are 23 pairs of chromosomes in humans inherited from our parents, with each parent contributing one half of each pair. Chromosomes are made up of DNA, 22 pairs are autosomes and the last pair is a sex chromosome fig 2 shows this. Autosomes are chromosomes that are not sex chromosomes; they are individual which means that each person has a DNA profile as unique as a fingerprint. No two DNA profiles or fingerprints can be the same due to the combination of marker sizes found in each person makes up his/her unique genetic profile. When determining the relationship between two individuals, their genetic profiles are compared to see if they share the same inheritance patterns at a conclusive rate.

Chromosomes are located in the nucleus of each cell and consist of long DNA strands where they are tightly packed and coiled around specific proteins called histones, which are looped and fixed to specific regions of the chromosome. There are 5 different kinds of histones (H1, H2A H2B, H3 and H4); they all bind to DNA to form chromatin in the nucleus during cell division where the chromatin condenses into visible structures that are the chromosomes itself. The DNA wrapped around each histone core is 200bp (base pair) long. Histones can be purified from DNA as H2A and H2B stick together as do H3 and H4 therefore making 8 proteins in each histone core with DNA wrapped is called a nucleosome which is 10nm (nano meter) fibre thickness, H1 is not part of the histone core as it binds to the nucleosome to...
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