Page 73 - Veritas - 02.03.22

What is the forensic significance of touch DNA?

As per the exchange principle proposed by the French criminologist

Edmund Locard, whenever two objects come in contact, there occurs

a transfer of material between them. This principle highlights the

significance of touch DNA as trace evidence. Touch DNA is highly ef-

fective in generating DNA profiles when biological fluids like blood,

semen, saliva are unavailable for DNA extraction. Therefore, it finds

importance in sexual assault, murder, homicide, burglary, and ques-

tioned documents cases.

What are the possible substrates on which touch DNA could be de-

posited?

Essentially, physical contact with any items like clothing, steering

wheels, mugs, door handles, knobs, windows, ropes, ligatures, docu-

ments, firearms can leave behind touch DNA.

What factors affect the amount of touch DNA transferred?

• Shedder status - Shedder refers to the individual handling an ob-

ject, causing transfer of touch DNA. Individuals who left behind

adequate amounts of touch DNA capable of generating complete

DNA profiles immediately after washing hands are termed “good

shedders” (tend to shed skin cells at a greater rate than others). The

distinction between “good” and “bad” shedders remains debatable

as the shedding of skin cells can depend on certain environmental

factors or age, leading to a different shedding status each day.

• Perspiration - Sweat can contain epithelial cells from the sweat

glands, contributing to more touch DNA on a surface of contact.

It may also carry away certain cells from the skin surface, increas-

ing the amount of transfer DNA. Additionally, when individuals

touch their face, eyes, nose, or hair, there occurs a transfer of DNA

from that area which Wickenheiser (2002) termed as “loading” of

fingers with DNA.

• Type of contact - Studies conducted by Goray and others (2010) led

to findings that increased pressure applied on the surface along

with the friction that comes into play increased the amount of

transferred DNA.