Opinion ID: 1506658
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Heading: Deoxyribonucleic Acid (DNA)

Text: Deoxyribonucleic acid (DNA) is a molecule of genetic materials shaped like a double-helix or spiral ladder. In every person, each cell with a nucleus contains a copy of that person's DNA. Thus, DNA serves as a blueprint for the human body. The sides of the DNA helix or ladder are composed of two chains comprised of sugars and phosphates. Rungs or steps connect the two sides of the ladder. The rungs consist of pairs of molecules called bases or nucleotides, which consist of four types: adenine (A), cytosine (C), guanine (G), and thymine (T). Nucleotides from separate DNA strands bond in a specific order to form the rungs that connect the sides of the DNA ladder. C bonds only with G, and A bonds only with T. Thus, for example, if the nucleotides on one strand are CGAT, the corresponding nucleotides on the attached strand will be GCTA. The order of the base pairs along the DNA molecule comprises an individual's genetic code. Human DNA contains approximately three to four billion base pairs, known as the genome. These base pairs govern the production of bodily proteins. A gene is a sequence of nucleotides on a DNA strand responsible for producing a particular protein. The sequence of the nucleotides can vary. The possible sequences or variations are called alleles. Thus, an allele is simply a version of a gene. A gene's position on a chromosome is its locus. In different individuals, genes may be polymorphic, meaning that they may take different forms or contain different sequences of base pairs. The polymorphic genes, which vary from one person to another, provide the basis for DNA identification. Most DNA has no known function, but even non-functional DNA remains important in forensic analysis. During mitosis, or cell division, each chromosome is copied. The paired nucleotides separate, dividing the chromosome's DNA molecule into two separate strands. Free-floating nucleotides attach to the exposed nucleotides of the separated strands in accordance with the G-C, A-T rule. Thus, each strand reconstitutes identical DNA molecules. When the cell divides, these two identical chromosomes enter newly-created daughter cells. Each new cell has the identical genetic composition as the original cell. All cells contain the same chromosomal composition. No two individuals, except identical twins, have the same nucleotide sequences throughout their DNA. DNA testing conducted on cells from various parts of the same body, whether blood, skin, semen, saliva, or hair will yield the same results. As in this case, DNA analysis can help identify donors of genetic material, such as blood.