1. Week 2 VNTR Summary

Junk DNA and Forensics

  • Important in forensics for DNA profiling.

  • Approx. 80% of human genome considered "junk DNA".

Genes and Alleles

  • Genes spread unevenly in chromosomes; may vary slightly (alleles).

  • Maximum of 2 alleles per gene; separated by non-gene regions.

Polymorphisms

  • Variations in DNA (sequence or length) among individuals.

  • Common in both gene and non-gene regions.

VNTRs Overview

  • Variable Number Tandem Repeats (VNTRs) are size polymorphisms found in DNA.

  • Comprise small repeated fragments (6-100bp).

VNTR Terminology

  • Repeat Unit: Bases in the repeat (e.g., 6bp).

  • Repeat Sequence: Exact base sequence in repeat.

  • Copy Number: Consecutive copies of repeat unit.

VNTR Identification

  • Developed by Alec Jeffreys in 1985; creates DNA fingerprints.

  • Patterns unique and inherited, useful for identification.

Location and Formation

  • VNTRs often located near telomeres, occurring due to replication mistakes.

  • Changes in VNTR number linked to polymerase slippage.

Steps in VNTR Testing

  1. DNA Collection

  2. Restriction Enzyme Digestion

  3. Gel Electrophoresis

  4. Southern Blotting

  5. Probing

Restriction Enzymes

  • Cuts DNA at specific sequences; crucial for VNTR testing.

  • Produces blunt or sticky ends depending on cut location.

Electrophoresis

  • Method for separating DNA fragments by size using electrical current.

  • DNA fragments migrate through a gel; smaller fragments move further.

Southern Blotting

  • Transfers DNA fragments from gel to a more stable nitrocellulose membrane.

Probing

  • Utilizes complementary base pairing to detect VNTRs; probes are labeled with tags.

Application of VNTRs

  • Used in criminal cases and paternity testing.

  • Single-locus VNTRs for faster results and reduced contamination risk.

Probability and VNTRs

  • The likelihood of sharing identical VNTR patterns is low.

  • More VNTRs tested reduce the chance of random matches.

  • Combination calculations for unique allele patterns detailed.

Key Takeaways

  • Understand VNTR characteristics and testing steps.

  • Know the roles and types of restriction enzymes.

  • Familiarity with electrophoresis process and its applications in forensics.