INTERPOL HANDBOOK ON DNA DATA EXCHANGE AND PRACTICE

APPENDIX 3what is forensic dna profiling?basic dna principles - the structure of dnaNuclear DNA molecules are made up of two strands that wrap around each otherin a helix to resemble a twisted ladder. The rungs of the ladder are made up of pairsof smaller molecules (monomers) called bases. There are four different bases presentin DNA: adenine (A), cytosine (C), guanine (G), and thymine (T). Each base only bindswith a specific complementary base - A with T and G with C. The binding of twocomplementary bases to form a ladder rung is called a base pair.Figure 7: Structure of nuclear DNAthe human genomeThe human genome consists of approximately six billion base pairs along forty-sixDNA molecules contained in twenty-three pairs of chromosomes in each cell nucleus.The order of bases along the DNA molecules is known as the DNA sequence.A gene is a particular area of a DNA molecule where the sequence of bases carriesinformation required to produce a particular protein from a particular sequence ofamino acids. Proteins provide the structural units for living organisms. Genes can varyin size, but average about 3,000 base pairs in length. Human DNA contains an estimated30,000 genes. Therefore, genetic or coding DNA makes up less than 5% of total humanDNA. The remainder of the DNA is non-coding DNA.Some areas of non-coding DNA are consistent across all people, while other areasvary significantly between individuals. It is this variability that provides the basis fordistinguishing between individuals through DNA profiling.APPENDIX 3what is forensic dna profiling?PAGE 87