Investigating the crime forensics use all possible evidences and materials that could be found at the crime scene, for instance, blood, DNA, mitochondrial DNA and so forth. Blood is fluid connective tissue that fills the cardiovascular system of vertebrates, including humans, and some invertebrates. Plasma (52-60%) and formed elements (40-48%) are two main components of it.
Plasma contains water and dissolved substances such as proteins and other organic and mineral compounds. Albumin, globulin and fibrinogen are the main plasma proteins. Water composes about 90% of plasma. Inorganic substances such as cations and anions form about 1%. Organic substances are divided into nitrogenous (proteins, amino acids, urea, creatinine, ammonia, metabolites of purine and pyrimidine nucleotides), and nitrogen-free (glucose, fatty acids, pyruvic, lactate, phospholipids, cholesterol). Plasma also contains gazes (oxygen and carbon dioxide) and active substances (hormones, vitamins, enzymes and neurotransmitters).
Blood formed elements are represented by erythrocytes, platelets and leukocytes. Erythrocytes or red blood cells are the most numerous among formed elements. Mature erythrocytes contain no nucleus and have a shape of biconcave discs. Red blood cells contain protein bearing iron – hemoglobin. Platelets or thrombocytes are limited by cell membrane fragments of cytoplasm of giant cells in marrow megakaryocytes. White blood cells or leukocytes are the part of the immune system. They are involved in immune reactions, excreting the T-cells that recognize the virus and all sorts of harmful substances, and B-cells that produce antibodies, macrophages, which destroy these substances (Hess 2009).
Deoxyribonucleic acid (DNA) is a macromolecule that provides storage, transmission from generation to generation and implementation of the genetic program of development and functioning of living organisms. Each chromosome, which is located in the cell nucleus, consists of two parts connected by a bridge. Both parts contain chromatin, which is heavily compacted before the cell divides, and form spiral-shaped filaments which are called chromatids. The latter contain a molecule of deoxyribonucleic acid, or DNA, which is the carrier of genetic information (genome) (Tong 2009).
DNA resembles twisted stairs in its structure, and therefore it is also defined as a double spiral. It consists of two very thin filaments, which are connected by bridges. Nucleotides are the structural units of this spiral. Each nucleotide consists of three parts which are sugar, phosphoric acid residue and a nitrogenous basis (adenine, thymine, cytosine or guanine).
Two bases, adenine – thymine and cytosine – guanine, form spiral stairs steps, being connected with each other via hydrogen links. Phosphoric acid residues form a stair railing, and sugar molecules are the connecting links of a DNA chain. Separate fragments, which are called genes, compose DNA molecule.
Mitochondrial DNA (mtDNA) is DNA contained in mitochondria, the organelles of eukaryotic cells. Mitochondrial DNA is a closed circular double-stranded molecule which has 16 569 base pairs in human cells what is relatively small amount comparing with the total DNA in cells. In general, mtDNA encodes two rRNA, 22 tRNAs and 13 subunits of respiratory chain enzymes, which is no more than half of proteins found in it. In particular, seven subunits of ATP-synthases, three cytochrome oxidase subunits and one subunit of ubiquinol-cytochrome-c-reductase are encoded under the control of mitochondrial genome. Moreover, all proteins, except for one, two ribosomal and six tRNAs are transcribed from a heavy DNA chain, and 14 other tRNA and a protein are transcribed from the lighter DNA chain (Bond 2007).
Knowledge about these unique forms of biological evidence can be used to identify or eliminate suspects in a crime. DNA dactylography is method which is used in forensic identification of individuals according to the unique DNA sequences which individual has. Although 99.9% of human DNA sequences have the same composition, nevertheless DNA of different people is quite unique. In DNA profiling, repetitive elements in the selected portion of the genome are analysed (Takayanagi 2003).
The process starts with the preparation of the DNA sample. The buccal (cheek) swab is the most preferred method of the reference sample selection. If this is not possible to take it in this way, other methods to collect samples of blood, saliva, semen, or other suitable fluid or tissue from personal items can be used. Samples obtained from blood of biological relatives, can serve as an indicator of an individual profile, as well as human remains, which were previously profiled. Afterwards, the control sample is analyzed to generate individual’s DNA profile to determine whether there are genetic similarities.
At the present time the DNA profiling is based on the polymerase chain reaction (PCR) and uses short tandem repeats (STR). This method analyzes the areas which have a high degree of polymorphism and short repeated sequences. These DNA segments can be used to distinguish between individuals (McCartney 2006).
It is sometimes impossible to obtain complete information on the short tandem repeats for highly degraded samples. In such situations, mtDNA is analyzed because there are many copies of mtDNA in the cell, whereas nuclear DNA can have no more than 1-2 copies. Mitochondrial analysis is a useful adjunct in determining the precise identification in such cases as the search for missing persons, when there are relatives related through the maternal line only.
Analysis of mtDNA is carried out in population studies. Polymorphism of mtDNA is widely used to establish the degree of divergence between different human populations.
Bond, John W. Value of DNA Evidence in Detecting Crime. Journal of Forensic Sciences, January 2007, Volume 52, Number 1, pp. 128-136. Print.
Hess, Karen M., Orthmann, Christine Hess. Criminal Investigation. 2009. pp. 142-143. Print.
McCartney, Carole. The DNA Expansion Programme and Criminal Investigation. British Journal of Criminology, March 2006, Volume 46, Number 2, pp. 175-182. Print.
Takayanagi, K., Asamura, H., Tsukada, K., Ota, M., Saito, S., Fukushima, H. Investigation of DNA extraction from hair shafts. International Congress Series, January 2003, Volume 1239, Number 69, pp. 759-764. Print.
Tong, Stephen., Bryant, Robin P., Horvath, Miranda A. H. Understanding Criminal Investigation. 2009. pp. 101-102. Print.