DNA Fingerprinting

Genetic Coding: Only about 5% of DNA is used for genetic coding; the rest consists of redundant or silent segments.
Repetitive DNA: These redundant segments contain 200 to 14,000 repeats of identical sequences on each DNA strand.
Individual Variation: The length, constitution, and number of repetitive sequences differ for each person, uniquely identifying individuals.
Stable Inheritance: Repetitive sequences are stably inherited in a Mendelian fashion.
Uniqueness: DNA fingerprinting is as unique as fingerprints to an individual.

Sample Collection:
- DNA can be extracted from various sources: blood, semen, tooth pulp, bone marrow, hair roots, muscle, and skin.
Fragmentation and Sequencing:
- DNA is cut into fragments at specific base sequences using restriction enzymes.
- These fragments are then repeated several times.
Electrophoresis and Blotting:
- Double-stranded DNA is denatured into single strands.
- DNA fragments are separated by gel electrophoresis, forming bands.
- Fragments are transferred to nitrocellulose sheets using Southern blotting.
DNA Probe and Detection:
- The membrane is exposed to a DNA probe (radioactive phosphorus-32) that binds to core sequences.
- X-ray film detects radioactive patterns, appearing as parallel bands or bars.
Comparison and Uniqueness:
- Compare patterns with other samples.
- The chance of two people sharing the same sequence is one in thirty thousand billion.

Blood Matching:
- DNA fingerprinting can match blood on a weapon to that of a victim.
Hair Roots and Accused:
- Hair roots found on a weapon can be matched with the blood of both the victim and the accused.
Seminal Fluid Evidence:
- Seminal fluid from the victim can be matched with the blood of the accused.
Exoneration and Paternity:
- Exonerate falsely implicated individuals.
- Positively establish paternity.
Pedigree Tracing and Identity:
- Trace family pedigrees.
- Identify unknown persons by matching prints with suspected parents or close relatives.