A DNA Match is NOT Sufficient to Prove Guilt

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DNA is the "master molecule of life". In every living creature from the amoebas to zebras, it carries the coded messages of heredity, governing everything from eye color to allergies. Its discovery solved by James Watson and Francis Crick 41 years ago has brought on one scientific triumph after another. Shelley and I explored these findings and presented the class with the most applicable use of DNA in society today--DNA and its service to the sensational field of criminal investigation. As such, our aim was to first explain the structure of DNA, the two methods of analysis used to examine DNA, the contentions one might have using these methods and then finally its impact on the field of forensics. In the following text of information, I will explain the former aspect of DNA and give a thorough explanation of its scientific make-up and the means used to analyze this "master molecule of life".

Within the nucleus of the cell, there is a ribbon of the huge molecule DNA, deoxyribonucleic acid, distributed over 23 chromosomes. Only a few microns wide, it would stretch a full six feet if uncoiled. It consists of 2 matching strands twisted in a spiral called a "double helix". Each strand contains some 3 billion repeating chemical units called nucleotides, each incorporating one of four different kinds of chemical bases--adenine, cytosine, guanine and thymine. The DNA of the two strands are complimentary and as such, only guanine links with cytosine and adenine with thymine. Hidden among these sequences and representing only 2% of human DNA are the genes-sequences that code for the production of the proteins all life depends on. Humans have an estimated 50,000 to 100,000 genes each made of 1,000 to some 2 million nucleotides with their bases. This great number afforded by the arrangement of these four bases reveals the secret to the vast info-carrying ability of the genetic code. The rest of the human genome, about 98%, is non-coding "junk" DNA.

It was only 8 years ago that DNA was introduced to the field of criminal investigation. Prior to that, it had been used as a means to identify the genes for inherited diseases such as Huntington's and cystic fibrosis. It was first established to be used in paternity and immigration cases; however, it was later used in 1986 as reliable and substantial evidence to convict Colin Pitchfork of murder.

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