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1. Forensic Serology & DNA Typing…
M.PHOOL BADSHAH

2. Lecture-10
Methods for Measuring DNA
Variations

3. Introduction
• In forensic research, the examination of DNA variants is crucial to
the identification of persons and the establishment of interpersonal
links.
• Numerous techniques exist for quantifying DNA variants, each with
specific benefits and uses.
• Some common methods used in forensic DNA analysis are:
1- PCR
2- STR
3- SNPs
4- mtDNA
5- DNA methylation
6- NGS
7- Capillary Electrophoresis

4. 1- PCR, or Polymerase Chain Reaction:
• Purpose: PCR is a widely used method for amplifying specific DNA
segments.
• Application: This approach amplifies regions of interest, such as short
tandem repeats (STRs), which are commonly used in forensic DNA profiling.
• Procedure: Heat-stable DNA polymerase and DNA primers are used to
selectively replicate the target region after heating DNA to separate its
strands.
2- Short Tandem Repeat (STR) Analysis:
• Purpose: Purpose of STR analysis is to pinpoint specific loci with brief DNA
sequence repeats.
• Application: STRs are widely used in forensic DNA profiling since
individual variations in STRs are substantial.
• Procedure: The lengths of the STRs are determined by capillary
electrophoresis, which separates DNA fragments based on size, after PCR
amplification.

5. 3- Analysis of Single Nucleotide Polymorphisms (SNPs):
• Single base pair variations in the DNA sequence are known as SNPs.
• Application: SNP analysis is used in population genetics, ancestry studies,
and human identification.
• Procedure: TaqMan assays and SNP arrays are used to identify specific
SNP variants.
4- Sequencing of mitochondrial DNA (mtDNA):
• The main purpose is to analyze the mitochondrial DNA inherited from
mothers.
• Application: Beneficial for research on maternal ancestry, especially when
nuclear DNA is absent or degraded.
• Procedure: PCR is used to amplify the mitochondrial DNA, which is
subsequently sequenced.

6. 5- DNA Methylation Analysis:
• Purpose: DNA methylation is the process of adding methyl groups to
cytosine nucleotides.
• Application: Forensic epigenetics for tissue identification and age
determination.
• Process: Techniques like bisulfate sequencing are employed to assess DNA
methylation patterns.
6- Sequencing Next-Generation (NGS):
• Purpose: High-throughput sequencing of DNA fragments is the goal.
• Application: NGS is a useful tool for doing in-depth genomic analyses,
which include identifying structural variants and mutations.
• Procedure: DNA is broken up into smaller pieces, and each piece's
sequence is ascertained independently.

7. 7- Capillary Electrophoresis:
• Capillary electrophoresis is used to separate and examine DNA fragments
based on their size.
• Application: Often used in conjunction with PCR for STR profiling and
other fragment analysis applications.
• Procedure: Amplified DNA fragments are identified using fluorescent
dyes, and then they are sorted in a capillary tube based on size.
• To produce a more thorough analysis, these techniques are frequently
combined, enabling forensic scientists to produce a precise and in-depth
profile for identification purposes. The particulars of the case, the caliber of
the DNA sample, and the data required for analysis all influence the
method selection.