This slide contains basic information about the concept of heredity, the meaning of genes and DNA and also the method of DNA profiling.

1. DNA: Heredity, Structure,
Sequencing & Profiling

2. o Paternity tests
o Rape/ Gang rape
o Murder/ Multiple murder from the same weapon
o Post- blast cases
o Organ transplantation
o Identification of body parts bodies
DNA test= 100% identification of individual
Forensic Importance of DNA Tests

3. Heredity
o It refers to the transmission of genetic
characteristics from one generation to another.
o Genetic characteristics are transferred through
genes and chromosomes.
o Genes and chromosomes are made up of a specific
chemical substance called DNA.

4. What are chromosomes?
 Chromosomes are made up of
thread-like structures present in
nucleus of cell.
 All living animals and plants are
made up of the same type of
genetic material but what
distinguishes one species from
another is the number of
chromosomes present in the
species. For example, human
beings have a total of 46
chromosomes, dinosaurs used to
have 400 chromosomes.

6. What are genes?
o Gene is that portion of
DNA which controls a
specific trait.
o Every gene has an
individual characteristic
and independent effect.
o For example, traits such as
eye color or hair color.

8. Paired Condition
o Genes and chromosomes are always present in pairs.
o Genes are present in pairs because for each specific
trait, one gene is inherited from the mother and
other is inherited from the father.
o There are 46 chromosomes in a human being, so,
there are actually 23 pairs of chromosomes.

10. Principles of Heredity
I. Law of Segregation
II. Law of Independent
Assortment
III. Law of Dominance

11. I . Law of Segregation
o We know that human being is a creature formed with
46 chromosomes. So, if 46 chromosomes are
inherited from the mother and 46 chromosomes are
inherited from the father, the offspring will have 92
chromosomes, which is not possible if the offspring
has to be a human being.
o We also know that for each genetic trait two genes
are present both in the mother and the father. But
the offspring takes only one gene from the mother
and one from the father. How does this happen?

12. Meiosis/ Reduction Division
 A special type of cell division called reduction
division takes place in the testis of the father and
ovaries of the mother such that the sperm of the
father and the ovum of the mother contains only 23
chromosomes and only one gene for a specific trait.
The genes which are present in pairs are separated
from each other through meiosis.

13. MEIOSIS
FATHER
Location:
Testis
MOTHER
Location:
Ovaries
46 46
23 23 23 23
23 2323
23
Spermatozoa Ovum

14. Fertilization23 23
46
Zygote
The zygote contains a unique
combination of DNA from both
parents. This zygote divides and
multiplies into an embryo and later, a
full human being.
This is the reason why DNA profile
can be obtained from any part of the
body.
Embryo
At fertilization, when spermatozoa and
ovum reunite, the paired condition
and the required number of
chromosomes are restored in the
offspring.

15. II. Law of Independent Assortment
Traits are transferred independently of each other.
Pairs of genes separate independently of each
other. This means that selection of a particular
gene during segregation for one particular trait has
nothing to do with selection of any other gene for
any other trait.

16. III. Law of Dominance
For each individual trait, a pair of genes is present.
The genes present in the pair may be identical to
each other or different from each other. Example:
(blood-group)
M F
A A
AA
M F
A O
AO

17. Generally, genes are of two types,
dominant and recessive. When, for a
specific trait, one gene is dominant and
other gene is recessive, only the
effective of dominant gene will be
expressed in the traits and the effect of
recessive gene is concealed. The effect
of recessive gene is visible in the traits
only when the dominant gene is absent.

18. Attached and Detached Earlobes
 Attached Earlobe: e (recessive)
 Detached Earlobe: E (dominant)
 Genetic combination for
Detached Earlobe: EE or Ee
 Genetic Combination for
Attached Earlobe: ee

19. Blood Grouping
Gene Dominant/Recessive
A Dominant
B Dominant
o Recessive

20. M F
A A
AA
M F
A O
AO
O
OO
M F
O
M F
A B
AB

21. M F
AO BO
A Group B Group
AB AO
BO OO
A
O
OB
M
F

22. DNA Test vs. Blood-Groupingantigens
RBC
Earlier, blood grouping was used for
identification of criminals and in paternity
tests. After the development of DNA
Finger-printing technique, blood-grouping
has become obsolete.

23. 1. DNA Test assures 100% identification of
individual. Many persons may have similar
blood group. If we have only the blood group,
in order to establish guilt of the accused, we
need other physical evidence or witness
testimony. Through blood test, we only come to
know the blood group of a person for example
A group or AB group. But, through DNA test,
we come to know not only the blood group but
also the genetic combination for that group for
example, AB, AA, AO etc.

24. 2. DNA can be obtained from semen (in rape
cases), saliva, blood, or skin cells. Blood
group may be obtained from these fluids if a
person is a secretors, but if a person is not a
secretor, blood sample is needed which may
not be found at a crime scene.

25. Sources of Evidence
 Semen recovered from the victim’s body. They are
collected through swabs of cotton. They are called
vaginal swabs.
 DNA Samples from Suspect 1 and Suspect 2
(maybe collected from saliva or semen or blood
samples; cheek swabs/buccal swabs may also be
used)

26. 3. DNA is present in internal structure of cell, that is, the nucleus. It
is protected by the cell membrane and nuclear membrane. But,
antigens are present as a protective layer external to the RBC. If not
collected on time, antigens are likely to get disintegrated due to
environmental factors like dust, moisture etc. If this happens, then
the blood-group cannot be detected.
antigens
RBC

27. 4. Upon examination of semen recovered
from the victim’s body, we come to know
whether the semen contains the DNA of a
single person or of multiple persons. (Rape
or Gang rape). The same rules also apply to
case of murder where blood samples of the
criminal may be left at crime scene or on
victim’s clothes. We can come to know the
number of suspected persons through blood
grouping also, but DNA profiling has a
higher degree of accuracy.

28. Structure of
DNA

29. S
S
SS
S
S
P
P
P
PP
P
The Helixes
o DNA is a double helical structure.
The helix are bilaterally symmetrical
to each other. These helixes are
made up of two components:
o Phosphorus (P)
o Sugar (S)
o These Phosphorus and Sugars are
joined by Hydrogen bonds.
Base Pairs
Helixes

30. The Base
Pairs
•Base Pairs are made
up of 4 bases:
•Adenine (A)
•Thymine (T)
•Cytosine (c)
•Guanine (G)
•The principle of base
pairs states that (T)
always binds with (A)
and (G) always binds
with (C).

31. Human
Genome
contains
approximately
3 billion base
pairs.

32. DNA Sequencing
 It is the process of determining the precise order of
the bases A, G, C, T within a strand of DNA.
 The sequence of these "letters" determines the
function of a piece of DNA.
 The identity of an individual person is by their
sequencing pattern.
Name of Individual DNA
Ram ACTAGGC
Shyam GTACTAA

33. DNA Fingerprinting
Dr. Alec Jaffreys Dr. V N Mathur
1980s

34. DNA Fingerprinting
 It is also known as DNA Profiling or DNA testing.
 Every individual organism is unique. Like
fingerprints, each person has a unique sequence of
DNA. Hence, the term used is “DNA Fingerprinting”.
 Unlike sequencing, fingerprinting does not attempt
to determine sequence. The goal of fingerprinting is
to determine whether a sample of DNA-containing
material like blood came from a given individual.
1980s

35. DNA Fingerprinting
 While certain regions of DNA are similar in all
individuals, there are certain other regions which differ
from one person to another.
 Regions of DNA contain sequences which keep
repeating.
 The repeating sequences are themselves the same in all
individual. But the number of times the repetitions occur
tends to vary from person to person.
 By comparing the number of such repeats, DNA profiles
are matched.

36. A T C G T C G T C G A C T A C G G C T A
A C A T G T C G T C G T C G T C G T C G
PERSON 1
PERSON 2
A T C A
A C T G C A

37. A T C G T C G T C G A C T A C G G C T A
DNA is cut into small fragment through chemical
scissors (restriction enzymes). Greater the number of
repeats, higher will be the molecular weight of the
strand which has been cut.
A C A T G T C G T C G T C G T C G T C G
PERSON 2
PERSON 1

38. Gel Electrophoresis
 The broken fragments of DNA are put
into a gel. Gel contains positive
electrodes on one side and negative
electrodes on the other. DNA
fragments are placed on the negative
end of the electrode.
 In case of murder or rape, fragments
of DNA of suspected persons and of
crime scene are put into gel. In case
of paternity, fragments of DNA of
child, mother and alleged father are
put into gel.

39. Gel Electrophoresis
 Current is passed through the gel. Because DNA
molecules are negatively charged, the fragments
move from positive electrode to negative
electrode.
 The fragments which contain larger number of
repeating sequences are longer. The fragments
which contain smaller number of repeating
sequences are shorter.

41. When current is passed, shorter
fragments move faster and travel
greater distance as compared to longer
fragments. Thus, the fragments are
arranged according to size (i.e.
according to number of repetitions).
They can be matched.

42. Example: Paternity Test Case

43. Example: Murder Case

44. DNA Reports: Paternity Test Case
Conclusion: Alleged
father is the biological
father, the probability of
paternity is 99.99%.
Here, paternity is
practically proven.

45. DNA Reports: Paternity Test Case
Conclusion: Alleged
father is not the
biological father.
Probability of paternity
is 0.00%.

46. DNA Report: Rape Case
 Conclusion: Suspect
B is the criminal.

47. DNA Report: Gang-rape Case
Evidence
Sample
15, 17
15, 16, 18, 19
23, 27, 21
12, 13, 14, 15
Rape Gang-rape

48. Identical Twins
 World over, it
has been found
very difficult to
solve such
crime cases in
which one of
the identical
twins is
suspected to
have
committed the
crime.

49. Identical Twins
 Right after division of
the zygote, the twins
have exactly the same
genetic profile.
 But during
embryonic
development, many
genetic changes
occur. These changes
occur randomly and
are less likely to be
same in identical
twins.

50. Identical Twins
 Ordinarily, DNA tests will not detect these changes because only a short
section of DNA is examined, in a region which is known to be highly
variable among individuals. After birth also, the genetic development of
a person is influenced by environmental factors, diet etc.
 But, if the entire DNA, with all its genes, is sequenced, the differences
would show up. But this process is highly costly and time consuming.
 According to a new discovery in this field made in this field by British
scientists in 2015, the melting point of DNA of identical twins is
different. Thus, by heating DNA samples, we can find out the real
criminal.
Human Being = “Nature” + “Nurture”

51. What Is Not Genetically Transmitted?
FINGER-PRINTS!!!
 Fingerprints are a partially genetic feature. They are
influenced by random stresses experienced in the
womb.
 Prints of identical twins are likely to be more alike as
compared to fingerprints of two unrelated people; but
they are not identical.

52. Thank You!!