To date, over 360 people across the U.S. have been exonerated by DNA evidence. You may have heard of DNA exonerations before, but you might be wondering how it actually works. This is not a simple question, scientifically or legally, so this series of posts is designed to be a general overview and introduction. Today, we will start with the basics – what is DNA?
In order to understand how DNA testing works, we first need to go over what DNA actually is. DNA, or deoxyribonucleic acid, is our genetic code that gives us our own individual characteristics. It is a molecule that is present in every cell in the human body and is passed down from parent to child. Every individual’s DNA is unique (unless you are a twin).
Check out this video from Khan Academy for an explanation of DNA structure and how it replicates (which becomes more important in the next post). The gist is that DNA looks like a twisted ladder, called a double helix. The sides of the ladder are made up of sugar and phosphate groups, called a sugar-phosphate backbone, while the rungs are made up of base pairs: adenine-thymine pairs and guanine-cytosine pairs.
This double helix is technically two strands, or chains, coiled around one another. Each chain is made up of a string of nucleotides. A nucleotide is a molecular unit that contains a sugar (deoxyribose), a phosphate group, and one of the four bases (adenine, thymine, guanine, or cytosine).
The pattern of bases along the DNA strand is what makes up our genetic code. This pattern is what examiner’s use to compare one person’s DNA to an unknown sample collected from a crime scene. But more about that in our next post...
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