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Guide to DNA Fingerprinting

Guide to DNA Fingerprinting

Here is a guide to DNA fingerprinting explaining how modern use of DNA (Deoxyribonucleic acid) analysis is so common that most people aren’t aware of what it really even is.  It is a term casually used in crime dramas on television to identify perpetrators, DNA sequence analysis is used to identify paternity in child support cases and also to match parents and children in cases where the child was given up for adoption. But, what is it, exactly?

DNA 101

The biological makeup of every human being is programmed by the information stored in the cells, referred to as genetic traits. Those genetic traits are dictated by the chromosomes passed from the biological parents. Within those chromosomes are is a chemical substance or structure Deoxyribonucleic acid. This acid is a double-helix (a double strand) of genetic material. It is made up of proteins and a sugar-based backbone. The proteins, adenine, thymine, guanine and cytosine bond together in specific formations to create an idiosyncratic pattern based on a number of factors, but every person has their own unique strand.

The proteins form what is called the “base”. The proteins bond together specifically so that adenine (A) only bonds with thymine (T) and guanine (G) only bonds with cytosine (C). The top pattern, also referred to as the 5’ or “five prime”, and the bottom pattern, also referred to as the 3’ or “three prime”, attach going opposite directions with proteins on either side corresponding in a pattern that is unique to that specific strand, forming what is called a “base pair.”

What is DNA Fingerprinting?

DNA fingerprinting is the process of identifying the specific pattern within a particular person’s DNA. The chemical composition of DNA in any cell is always the same, but each person (or being) has a specific order in which the patterns repeat themselves. In order to use DNA as identification the same way that fingerprints are catalogued and used, every person would need their DNA tested and electronically filed in a database. The FBI sponsors a database for this purpose for use in solving crimes, called CODIS (Combined DNA Index System).

The way DNS is used to identify a specific person is related to the sequence of base pair patterns, rather than on one specific pattern. Base pairs in each person numbers in the millions, so scientists have to narrow that down. While these identified patterns cannot create a specific “fingerprint,” so to speak, they can reveal whether or not the identifiable strands are statistically likely to occur in the same person or related persons.

Method of Identifying DNA Strands

One method used is called the Southern Blot. The purpose of the Southern Blot is to extract a specific pattern of DNA strands by separating the nonessential cellular matter from the patterned DNA strand in the nucleus. Sometimes the extraneous material is washed away, but sometimes pressure is applied to force extraction.

Using bacterial enzymes, referred to as restriction enzymes, the DNA strands can be cut into varying pieces that will provide a glimpse of that particular DNA’s identifying pattern. Each enzyme will have a specific pattern that it cuts into DNA, making it a reliable and identifiable method. The DNA is separated by size after being poured into the electrophoresis gel, with the largest pieces on top and the smallest to the bottom, is called “size fractionation.” The DNA is then denatured through heat or chemical treatment, which means that it is cut into a single strand.

The fractionated DNA is then baked after being blotted into a sheet of nitrocellulose paper so it is attached to the sheet.

Southern Blot analysis uses a radioactive genetic probe in a hybridization reaction. This means a radioactive strand of DNA is used to draw out the specific attributes of the DNA being tested. The hybridization reaction is when the DNA being tested binds to the probe. An identifiable pattern belonging to a specific person will show up in an X-ray in red.

Variable Number Tandem Repeats

DNA strands can contain up to one hundred base pair of sequences Variable Number Tandem Repeats (VNTRs). Pieces of DNA with information that programs organism development are exons, while aspects that appear useless are introns, which is where the patterns are ascertained from. These patterns are typically genetic, with specific pattern types passed down from both parents. When the DNA is subjected to a hybridization reaction probe, the specific pattern can be identified.

What Is DNA Identification Used For?

Isolating the VNTR patterns from a variety of tissues in the human body can be essential in solving crimes, or the very least casting a strong likelihood of innocence or guilt of the party in question. It can also be used to identify remains.

The VNTR patterns may be used to conclusively determine paternity or maternity in some cases because the patterns are genetic.

As useful as it is, it can be problematic. Because its accuracy is not guaranteed, all it has to offer is a high probability of identification. Which means that the patterns may appear to match, but their consistencies might be superficial. Strands appear to be the same, but are not.

Specific characteristics in the DNA strands that appear common in people of different races might show similarities, but that is inconclusive at best and presents other legal and ethical issues.

The worst possible scenario is using DNA as a conclusive arbiter of truth, but for the analysis process to be marred by error. The sample could be labeled incorrectly, it could be tainted by the DNA specimen of someone else in contact with it, or the technician conducting the test could make a mistake.

Using DNA fingerprinting is a valuable process that has helped millions of people solve some of life’s most distressing quandaries. In conjunction with other types of reliable, factual data, DNA fingerprinting is proved to be an immutable ally.

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