Touch DNA refers to DNA collected from skin cells left on objects during physical contact, which significantly expands the types of evidence usable in forensic analysis. Unlike traditional methods requiring larger samples, Touch DNA can be collected from just a few cells, making it possible to identify suspects in various scenarios, including crime scenes. The process involves amplifying the DNA via polymerase chain reaction and creating a genetic profile using fluorescent compounds.

1. TOUCH DNA
Submitted by,
Athul k sabu
Dept of forensic science
St. Thomas college
Thrissur
Kerala

2. INTRODUCTION
 WHAT IS “ TOUCH DNA”?
 When an assailant leaves behind skin cells ,after touching
a victim , a weapon, or other items at crime scene .
 OR
 Touch DNA” is DNA obtained from biological material
transferred from a donor to an object or a person during
physical contact.

3.  The technique has dramatically increased the number of
items of evidence that can be used for DNA detection. In
the 1980s, in order to perform DNA analysis on a crime
scene or victim, forensic investigators needed a blood or
semen stain about the size of a quarter. The sample size
fell in the 1990s to the size of a dime and then became:
“If you can see it, you can analyze it.”
 Touch DNA doesn’t require you to see anything, or any
blood or semen at all. It only requires seven or eight cells
from the outermost layer of our skin.
 Every day thousands of exfoliated epithelial cells are
shedding from our skin which can form a source of DNA on
left over items.

4.  There will be so many contacts that will be left by the
criminals in the scene of crime like abandoned cloths,
kerchief, hat, footwear, tools used to gain entry, mobile
phones, weapons, used vehicles etc. which will bear his or
hers genetic signature in the form of cells.
 Generally a suspect can shed more cells than others when
they are nervous and they also shed when they are leaving
the crime scene.
 As the surface texture gets rougher the probability of
abrading skin cells reach higher. Stronger pressure applied
to the weapon leaves the sheding tissues more. In this way
we can expect cells for DNA analysis to identity presence
of culprit at the crime scene. (Exception in cyber crimes).

5. Here’s how it works:
 Investigators recover cells from the scene, then use a
process called polymerase chain reaction (PCR) to make
lots of copies of the genes. Next, scientists mix in
fluorescent compounds that attach themselves to 13
specific locations on the DNA and give a highly specific
genetic portrait of that person. The whole process takes a
few days, and forensic labs are often backed up analyzing
data from other cases.