The Application of Recombinant
DNA Technology In Forensic Science
Made by: Sara Hassan
Presented to:Dr.Amber Shehzadi
The application of scientific knowledge and methodology to
legal problems and criminal investigations is called forensic
it includes problems like paternity issues, exoneration,
criminal identification, high profile crimes
bases on CSI and evidence collected.
The applications of molecular biology, technologies and
genetics which center largely on the ability of DNA analysis of
the evidence recovered from the crime scene. In the popular
media, these techniques are called genetic fingerprinting,
though the more accurate term used today is DNA profiling.
DNA analysis consists of traditional and specializes
techniques to distinguish between individuals of
the same specie.
Described by Dr. Alec Jeffrey in 1985.
Traditional Techniques: Restriction fragment
length polymorphism (RFLP), and short tandem
repeat (STR) analysis.PCR analysis.
Specialized Techniques: mitochondrial DNA
(mtDNA) analysis, single nucleotide
polymorphism, or SNP.
PCR of STR regions
• PCR (polymerase chain reaction) analysis is usually the first
step in the creation of a DNA profile today.
• PCR replicates a small amount of DNA to create a larger
sample for analysis.
• It does this using a repeating process that takes about five
minutes. First, a heat-stable DNA polymerase -- a special
enzyme that binds to the DNA and allows it to replicate -- is
added. Next, the DNA sample is heated it to 200 degrees F (93
degrees C) to separate the threads. Then the sample is cooled
and reheated. Reheating doubles the number of copies. After
this process is repeated about 30 times, there is enough DNA
for further analysis.
• Restriction Fragment Length Polymorphism we digest our
DNA sample with restriction endonucleases
• These fragments are separated by gel
• Blotting is done.
• Probes are added
• Corresponding image on Xray film is taken.
Short Tandem Repeats (STR) analysis
• STR: repeated sequences of 3-5 base pairs (loci) which can be identified in a
known data base.
• Typically in non-coding intron region
• Very useful in DNA analysis because they show great variability among individuals.
Does not require very much DNA, can be coupled with PCR.
• (STR) technology evaluates specific regions (loci) that are found on DNA.
• The variable (polymorphic) nature of STR regions intensifies the discrimination
between one DNA profile and another.
• Tested by gel electrophoresis or capillary electrophoresis
A Y-STR is a (STR) on the Y-chromosome.
Y-STRs are used for paternity, and genealogical DNA testing.
Y-STRs are taken specifically from the male Y chromosome.
These Y-STRs provide a weaker analysis than autosomal STRs
because the Y chromosome is only found in males, which are
only passed down by the father, making the Y chromosome in
any paternal line practically identical.
• This causes a significantly smaller amount of distinction
between Y-STR samples. Autosomal STRs provide a much
stronger analytical power because of the random matching
that occurs between pairs of chromosomes during the zygote
• mtDNA technology analyzes DNA found in a different part of
the cell, the mitochondrion
• Old remains and evidence lacking nucleated cells — like hair
shafts, bones, and teeth — that are unamenable to STR and
RFLP testing yield results by mtDNA analysis.
• all maternal relatives (for example, a person's mother or
maternal grandmother) have identical mtDNA.
• This enables unidentified remains to be analyzed and
compared to the mtDNA profile of any maternal relative for
the purpose of aiding missing persons or unidentified
mtDNA gel image
Computer analysis and mtDNA profile
Mitochondrial DNA Analysis
• CODIS, which stands for Combined DNA Index System, is a
program which consists of many databases that have DNA
profiles useful for the criminal justice system
• NDIS, or National DNA Index System, is the part of CODIS that
contains DNA profiles at a national, state, and local level and
is accessible to law enforcement all over the country
Related individuals have similar DNA
Your DNA profile, like all other aspects of your genome, is inherited
partly from your mother and partly from your father.
Relationships within a family therefore become apparent when the
alleles of a particular STR are marked on the family pedigree
In this example, we see that 3 of the 4 children have inherited the
12-repeat allele from the father.
This observation in itself is not sufficient to deduce that these three
children are siblings, though the statistical chance would be quite
high if the 12-repeat allele was uncommon in the population as a
Mt DNA from maternal side, Y STR for paternal side,
STR alleles can be helpful for making a pedigree .