Genetic Identification: Restriction Enzymes to DNA Fingerprints

Understanding DNA Analysis Techniques

Restriction Enzymes: Cutting DNA with Precision

Role: Restriction enzymes cut foreign DNA into pieces to prevent infection.

Mechanism: Special proteins recognize specific DNA sequences (restriction sites) and cut at those locations. Bacteria protect their own DNA from self-cleavage using methylation.

Example: EcoRI

EcoRI recognizes the sequence GAATTC and cuts between G and A. This creates "sticky ends" (overhangs) like G- and AATT, which help join DNA fragments.

DNA Fragmentation and Gel Electrophoresis

DNA is cut into fragments using restriction enzymes. These fragments are then sorted by size using gel electrophoresis.

• Shorter fragments travel farther and faster in the gel.
• DNA fragments are stained for visibility, showing distinct bands.

Gel Electrophoresis: Process and Uses

Process:

1. DNA is loaded into a gel.
2. An electric current separates fragments based on size.
3. Bands on the gel represent fragment sizes.

Uses:

• Compare DNA for detecting mutations or analyzing individual differences.
• Identify changes in restriction sites or fragment lengths.

DNA Fingerprinting: VNTRs and STRs

VNTR (Variable Number of Tandem Repeats)

VNTRs are longer DNA sequences repeated back-to-back. Individuals have unique numbers of these repeats. Restriction enzymes cut around VNTR regions, creating DNA fingerprints.

STR (Short Tandem Repeats)

STRs are shorter DNA sequences. They are generally easier and faster to analyze compared to VNTRs.

DNA Fingerprinting Process and Applications

DNA fragments from gel electrophoresis can be transferred to a membrane and probed:

• Probes: Small, labeled DNA pieces that bind to specific sequences.
• Visualization: Probes make matching DNA visible as dark bands.

Applications:

• Identify individuals.
• Determine family relationships (inheritance of STRs from parents).

Properties and Forensic Use of STRs

STRs Properties:

• Unique to individuals.
• STR loci are inherited from both parents.

Forensic Use:

• Create DNA profiles for identification.
• STRs work well with smaller or degraded DNA samples.
• Machines analyze STR patterns to produce a DNA fingerprint.

Example:

Crime scene DNA is compared to suspects' DNA profiles. Mismatches prove innocence; matches confirm identity.

Advantages of STRs

• More efficient and precise than VNTRs.
• Require less DNA and work effectively with degraded samples.