Creating a DNA profile involves several steps, from collecting a sample to analyzing it and generating a unique genetic fingerprint. Here's a breakdown of the process:
Steps Involved in DNA Profiling
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Sample Collection: The first step is to collect a biological sample containing DNA. Common sources include:
- Blood
- Saliva
- Hair (with the root attached)
- Skin cells
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DNA Extraction: Once collected, the DNA must be extracted from the sample. This process involves:
- Cell Lysis: Breaking open the cells to release the DNA. This can be done chemically or physically (e.g., using heat). As the University of Arizona notes, bathing cells in hot water can assist in this process.
- DNA Purification: Separating the DNA from other cellular components (proteins, lipids, etc.). This often involves using a series of chemical solutions and centrifugation.
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DNA Amplification (PCR): Because the amount of DNA obtained from a sample may be small, a technique called Polymerase Chain Reaction (PCR) is used to amplify specific regions of the DNA. This process creates millions of copies of the targeted DNA sequences, making them easier to analyze.
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DNA Fragmentation (Restriction Enzymes - Historically): Historically, restriction enzymes were used to cut the DNA at specific sequences, creating fragments of varying lengths. However, modern DNA profiling primarily focuses on analyzing specific short tandem repeats (STRs) and largely avoids this step.
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STR Analysis: Modern DNA profiling primarily relies on analyzing Short Tandem Repeats (STRs). STRs are short DNA sequences that are repeated multiple times in a row. The number of repeats varies from person to person, making them highly informative for identification.
- Identifying STR Loci: Scientists analyze multiple STR loci (specific locations in the genome) simultaneously.
- Determining Repeat Lengths: The length of each STR at each locus is determined. This is often done using capillary electrophoresis, which separates DNA fragments based on size.
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Data Analysis and Profile Generation: The data from the STR analysis is then used to create a DNA profile. This profile typically consists of a series of numbers representing the number of repeats at each STR locus. This information is unique to each individual (except for identical twins).
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Profile Comparison and Interpretation: The generated DNA profile can then be compared to other profiles, such as those in a database or from a suspect in a criminal investigation. Statistical analysis is used to determine the likelihood that the two profiles match by chance.
Example
Imagine a blood sample is found at a crime scene. Scientists extract the DNA, amplify the STR regions using PCR, and then determine the number of repeats at several STR loci. The resulting profile might look something like this (simplified):
| STR Locus | Number of Repeats |
|---|---|
| D3S1358 | 15 |
| VWA | 17 |
| FGA | 22 |
This profile can then be compared to the profile of a suspect to determine if there's a match.
Summary
Creating a DNA profile is a multi-step process that involves collecting a sample, extracting and amplifying the DNA, analyzing STRs, and generating a unique genetic fingerprint. This profile can then be used for identification purposes in various fields, including forensics, paternity testing, and medical diagnostics.
