FOREBSIC SCIENCE

FORENSIC SCIENCEWWW.PCMBTODAY.COM

A

of DNA sequences unique to that species. Identifying

individuals within a species is less precise at this time,

although when DNA sequencing technologies progress

farther, direct comparison of very large DNA segments,

and possibly even whole genomes, will become feasible

and practical and will allow precise individual

identification.

To identify individuals, forensic scientists scan about

10 DNA regions that vary from person to person and

use the data to create a DNA profile of that individual

(sometimes called a DNA fingerprint). There is an

extremely small chance that another person has the same

DNA profile for a particular set of regions.

ny type of organism can be identified by examination

Is DNA effective in identifying persons?

DNA identification can be quite effective if used

intelligently. That means that those portions of the DNA

sequence that vary the most between humans must be

used; also, large enough portions must be used to

overcome the fact that human mating is not absolutely

random.

Consider the scenario of an crime scene investigation...

Assume that type O blood is found at the crime scene.

type O occurs in about 45 % of individuals. If investigators

only type for ABO, then finding that the “suspect” in a

crime is type O really doesn’t tell you very much.

If, in addition to being type O, the suspect is a foreigner,

and golden brown hair is found at the crime scene, then

you now have two bits of evidence to suggest that your

suspect really did it. However, there are a lot of type O

blonds out there.

If you find that the crime scene has footprints from a

pair of shoes (with a distinctive tread design) and the

suspect, in addition to being type O and blond, is also

wearing a particular type of shoes with the same tread

design, then you are much closer to linking the suspect

with the crime scene.

In this way, by accumulating bits of linking evidence in

a chain, where each bit by itself isn’t very strong but

the set of all of them together is very strong, you can

argue that your suspect really is the right person.

With DNA, the same kind of thinking is used; you can

look for matches (based on sequence, or on numbers of

small repeating units of DNA sequence) at a number of

different locations on the person’s genome; one or two

(even three) isn’t enough to be confident that the suspect

is the right one, but 4 (sometimes 5) are used and a match

at all 5 is rare enough that you (or a prosecutor or a

jury) can be very confident (“beyond a reasonable doubt”)

that the right person is accused.

Identity of a criminal is determined by comparing the

accused man's DNA fingerprint with that of the blood

or seminal stain found at the scene of crime. If the DNA

fingerprints are identical, there is an absolute

identification.

Currently, the most important tool used to make a paternity

determination is a blood test called a human leucocyte

antigen (HLA) test. It is based on the principle that the

genetic variation among individuals in partially reflected

in the kinds of proteins, called antigens, that are present

on their leucocytes. Because a child inherits half his

genetic information from his mother and half from his

father, his proteins should therefore be representative

of both parents. If, for example, the HLA test show that

none of an accused man's proteins are present on a child's

blood cells, then it can be said with nearly 100 percent

certainty that he is not the father of the child. If the

accused man's proteins are on the child's cells, than it

is highly likely that he is the father. The relationship,

however is not certain, because it is always possible that

another man with the same proteins fathered the child.

That is , the test falls short because the proteins used in

the HLA analysis are not unique to any individual. There

can be as much as 5 to 10 percent chance that a man

who is deemed the father is actually not. By contrast,

the DNA fingerprints are unique (except for indentical

twins). The DNA fingerprints are inherited as simple

Mendelian characters). Paternity is determined by

comparing the accused man's DNA fingerprints with that

of the child.

COPYRIGHT WWW.PCMBTODAY.COM

Some Examples of DNA Uses for Forensic

Identification

l

evidence left at crime scenes

identify potential suspects whose DNA may match

l

exonerate persons wrongly accused of crimes

l

identify crime and catastrophe victims

l

establish paternity and other family relationships

l

to wildlife officials (could be used for prosecuting

poachers)

identify endangered and protected species as an aid

l

air, water, soil, and food

detect bacteria and other organisms that may pollute

l

programs

match organ donors with recipients in transplant

l

determine pedigree for seed or livestock breeds

l

authenticate consumables such as caviar and wine

Major concern for the application of DNA finger

printing

There are certain concerns with the application of DNA

fingerprinting on medicolegal evidence samples.These

are-

1. Gene frequencies for the major population groups

must be established to provide a base for the

interpretation of findings.

2. Standard typing reagents should be available to the

forensic science community to allow independent

testing in different laboratories.

3. Methodological guidlines need to be defined to insure

reliability of test result.

4. Bloodstains would have to contain at least 50

blood to be amenable to analysis.

ml of

How is DNA typing done?

Only one-tenth of a single percent of DNA (about 3

million bases) differs from one person to the next.

Scientists can use these variable regions to generate a

DNA profile of an individual, using samples from blood,

bone, hair, and other body tissues and products.

In criminal cases, this generally involves obtaining

samples from crime-scene evidence and a suspect,

extracting the DNA, and analyzing it for the presence

of a set of specific DNA regions (markers).

Scientists find the markers in a DNA sample by designing

small pieces of DNA (probes) that will each seek out

and bind to a complementary DNA sequence in the

sample. A series of probes bound to a DNA sample creates

a distinctive pattern for an individual. Forensic scientists

compare these DNA profiles to determine whether the

suspect’s sample matches the evidence sample. A marker

by itself usually is not unique to an individual; if, however,

two DNA samples are alike at four or five regions, odds

are great that the samples are from the same person.

If the sample profiles don’t match, the person did not

contribute the DNA at the crime scene.

If the patterns match, it means that the suspect may have

contributed the evidence sample. While there is a chance

that someone else has the same DNA profile for a

particular probe set, the odds are exceedingly slim. The

question is, How small do they have to be when conviction

of the guilty or acquittal of the - innocent lies in the

balance? Many judges consider this a matter for a jury

to take into consideration along with other evidence in

the case. Experts point out that using DNA forensic

technology is far superior to eyewitness accounts, where

the odds for correct identification are about 50:50.

Steps involved in DNA finger printing

.

extracted from almost any human

tissue. Sources of DNA found at a

crime scene might include blood,

semen, tissue from a deceased victim,

cells in a hair follicle, and even saliva.

DNA extracted from items of evidence is compared to

DNA extracted from reference samples from known

individuals, normally from blood.

DNA extraction – DNA can be



restriction endonuclease–

Digestion of DNA with a

Extracted DNA is treated with

a restriction endonuclease,

which is an enzyme that will

cut double stranded DNA whenever a specific DNA

sequence occurs. The enzyme most commonly used for

forensic DNA analysis is HaeIII, which cuts DNA at

the sequence 5'-GGCC-3'.

.

electrophoresis –

DNA digestion, the resulting

DNA fragments are separated

by size via electrophoresis in

agarose gels. During electrophoresis, DNAs which are

negatively charged migrate toward the positive electrode.

As DNAs move, their migration rate is slowed by the

matrix of the agarose gel. Smaller DNAs move more

rapidly through the pores of the gel matrix than larger

DNAs. The result is a continuous separation of the DNA

fragments according to size, with the smallest DNA

fragments moving the greatest distance away from the

origin.

Agarose gelFollowing



Preparation of a “southern blot” – Following

COPYRIGHT WWW.PCMBTODAY.COM

probe, the radioactivity on the Southern Blot can be

washed away with a high temperature solution, leaving

the DNA in place. The Southern Blot can be hybridized

with a second radioactive single locus probe, and by

repetition of steps 5-7, a series of different single locus

probes. The set of Autorads from a Southern Blot is

known as a “DNA Profile.”

Institutes where you can study forensic

science in India

If you are a student from India, you could join forensic

science in a number of ways. Many universities in India

offer M.Sc. Courses in Forensic Sciences. Main among

these are:

1. Punjabi University

course of M.Sc. in Forensic Science. There are ten seats

per batch. To be eligible you must have either of the

following: (i)B.Sc. (Medical/Non-Medical) (ii) BDS

(iii) MBBS. The university offers specialization in forensic

biology, forensic serology, forensic chemistry and forensic

toxicology.

, Patiala : It offers a two year

2. Department of Criminology and Forensic Science,

Dr. Hari Singh Gaur Vishwavidyalaya, Sagar, Sagar

University, Madhya Pradesh.

The department offers two Masters Degree courses. These

are M.A. (Master of Arts) in Criminology, and M.Sc.

(Master of Science) in Forensic Science and Forensic

Toxicology. Each course has 12 seats. The selection is

on merit basis. Admissions start in June every year (or

sometimes in July). These courses are also taught at

Graduate level (Both B.A. and B.Sc. Level). The

department has a well-equipped laboratory for conducting

experiments

Another course offered by this University is a six-month

Diploma course in Criminology and Forensic Science.

But this diploma is meant only for the Police officials

of the Madhya Pradesh State. Please contact the University

to check if you can be admitted to this course as a special

case. Research Programmes in Criminology and Forensic

Science are also conducted.

3. University of Chennai

This university offers an MA in Criminology. Eligibility

is a valid Bachelor’s degree.

, Chennai

4. Banaras Hindu University

This University offers an MA in Criminology. Eligibility

is a valid Bachelor’s degree.

, Varanasi, (UP)

5. Forensic House,

Chennai

This institute offers a course in Criminology and Forensic

electrophoresis, the separated

DNAs are denatured while still

in the agarose gel by soaking

the gel in a basic solution.

Following neutralization of the

basic solution, the single strand

DNAs are transferred to the surface of a nylon membrane

by blotting. This denaturation/blotting procedure is known

as a “Southern Blot” after the inventor, Ed Southern.

Just as the blotting of wet ink on a dry paper transfers

a replica of the image to the paper, the blotting of DNA

to a nylon membrane preserves the spatial arrangement

of the DNA fragments that existed after electrophoresis.

35A Kamarajan Salai, Mylapore,



probe

a DNA or RNA sequence that is

able to hybridize (i.e. form a DNADNA

or DNA-RNA duplex) with

DNA from a specific restriction

fragment on the Southern Blot. Duplex formation depends

on complementary base pairing between the DNA on

the Southern blot and the probe sequence. Single locus

probes are usually tagged with a radioactive label for

easy detection, and are chosen to detect one polymorphic

genetic locus on a single human chromosome. The

Southern Blot from step 4 is incubated in a solution

containing a radioactive, single locus probe under

conditions of temperature and salt concentration that

favor hybridization. After hybridization, the unbound

probe is washed away, so that the only radioactivity

remaining bound to the nylon membrane is associated

with the DNA of the targeted locus.

Hybridization with radioactive– A Single Locus Probe is

.

autoradiography

of radioactive probe hybridization

on the Southern Blot are detected

by Autoradiography. In this

technique, the washed nylon

membrane is placed next to a sheet of X-ray film in a

light tight container. The X-ray film records the locations

of radioactive decay. After exposure and development

of the X-ray film, the resulting record of the Southern

Hybridization is termed an “Autoradiograph”, or

“Autorad” for short.

Detection of RFLPs via– The locations

.

additional probes

forensics DNA analysis, DNA polymorphisms on several

different chromosomes are characterized. After an

Autorad has been developed for the first single locus

Re-probe southern blot with– In a typical

COPYRIGHT WWW.PCMBTODAY.COM

Science. Eligibility is a valid Bachelor’s degree in Physics,

Chemistry or Applied Science. MBBS, BDS, and

B.Pharm. students are also accepted.

6. Department of Criminology and Forensic Science,

Karnataka University, Dharwar 580003, Karnataka

India

Karnataka University offers M.A. (Masters in Arts) in

Criminology and M.Sc. in Forensic Science and Forensic

Toxicology. To be eligibile, you have to have a BA, B.Sc.

or B.Com. degree with a minimum of 50% aggregate.

The admission is through an entrance test.

7. Department of Forensic Science

Ambedkar University, Agra, U.P.

This University offers an M.Sc. in Forensic Science.

, Dr. B.R.

8. Tata Institute of Social Sciences

8313, Sion-Trombay Road Deonar, Mumbai

This institute offers Criminology as a specialization course

with Masters in Social Work programme.

, Post Box No.

9. Department of Anthropology

Delhi

It offers a certificate course in Forensic Science

, University of Delhi,

10. National Institute of Criminology and Forensic

Science

Sector III, Institutional Area, Outer Ring Road, Rohini,

Delhi-110085

This institute is a premier body conducting traning and

research in the field of Forensic Science. It offers research

programmes and diplomas in Forensic Science. Officials

who can attend these programs are police officers, forensic

scientists, judges, research scholars, and senior officials

from various forensic laboratories.

, Ministry of Home Affairs, Government of India,

11. Department of Anthropology

Pune, Maharashtra, India.

This University started a Masters course as well as a

P.G. Diploma course in Forensic Sciences in 2003.

In general, to be eligible for an M.Sc. Course in Forensic

Sciences in any of the above universities, you should

have a bachelor’s degree, preferably with a first division

in physics, chemistry, zoology, or botany. You can find

out about the details of admission to this course from

your local state university. Once you have done the M.Sc.

successfully you can even go for a Ph.D. in Forensic

Sciences. In your M.Sc. Course you can choose a field

of specialization such as forensic ballistics, forensic

entomology, forensic botany and so on.

, University of Pune,

For further details e-mail   TO sainto1380@gmail.com