Finding DNA involves identifying sources where it might be present and then using appropriate collection and extraction techniques.
Sources of DNA
DNA can be found in various biological materials. Common sources include:
- Bodily Fluids: Blood, saliva, semen, and urine are excellent sources.
- Tissues: Skin, hair roots, and bone contain DNA. Even shed skin cells can contain recoverable DNA.
- Items Touched: DNA can be transferred to objects through touch.
According to the reference material, some specific examples of places to look include:
- Drinking glasses
- Cigarette butts
- Food with bite marks
- Bite marks on skin
- Commonly touched surfaces like:
- Computer keyboards
- Door knobs
- Steering wheels
- Eyeglasses
- Countertops
Collection Techniques
Proper collection is crucial to prevent contamination and ensure the DNA sample's integrity.
- Swabbing: Use sterile swabs to collect samples from surfaces or bodily fluids.
- Cutting: Cut out portions of items containing potential DNA, such as fabric or cigarette butts.
- Scraping: Gently scrape surfaces to collect skin cells or other biological material.
Extraction Methods
Once collected, DNA must be extracted from the sample. Common methods include:
- Organic Extraction: Using chemicals like phenol and chloroform to separate DNA from proteins and other cellular debris.
- Solid-Phase Extraction: Binding DNA to a solid support, washing away impurities, and then eluting the purified DNA.
- Chelex Extraction: Using a resin to bind metal ions that can inhibit downstream DNA analysis.
- Magnetic Bead Extraction: Utilizing magnetic beads that selectively bind DNA, allowing for easy washing and elution.
The chosen extraction method depends on the sample type and the desired DNA purity and quantity. After extraction, the DNA is typically amplified using PCR (Polymerase Chain Reaction) for analysis.
