Why in News? DNA polymorphisms are
variations in DNA sequences that occur
naturally among individuals. These genetic
variations make each person's genetic
makeup unique and serve as the foundation
for DNA fingerprinting and identification.
What Are DNA Polymorphisms?
DNA polymorphisms are specific locations in
the genome where DNA sequences vary
between individuals. While approximately
99.9% of human DNA is identical across all
people, the remaining 0.1% contains these
variations that make each person genetically
unique. These polymorphic regions:
1) Occur throughout the genome in both coding
and non-coding regions
2) Can be inherited from parents, following
Mendelian inheritance patterns
3) Allow scientists to distinguish between
individuals at the genetic level
4) Form the basis for DNA fingerprinting and
forensic identification
Types of DNA Polymorphisms
Several types of DNA polymorphisms exist,
with Short Tandem Repeats (STRs) being
particularly useful for human identification:
1) Short Tandem Repeats (STRs): Short
sequences of base pairs that are repeated a
variable number of times, such as
GATCGATCGATCGATC
2) Single Nucleotide Polymorphisms (SNPs):
Variations in single nucleotides at specific
positions
3) Variable Number Tandem Repeats (VNTRs):
Longer repeated sequences that vary in
number between individuals
4) Insertions and Deletions: Where DNA
segments are either added or removed
How DNA Polymorphisms Differentiate
Between People?
DNA polymorphisms create unique genetic
profiles because:
1) Unrelated individuals almost certainly have
different numbers of repeat units in at least
some STRs
2) Each person inherits a unique combination of
polymorphisms from their parents
3) The probability of two unrelated individuals
sharing identical polymorphisms across
multiple sites is extremely low
4) These differences can be compiled into a
unique table called a DNA fingerprint
DNA Fingerprinting Process
To analyze DNA polymorphisms for
identification:
1) DNA is extracted from biological samples
(blood, saliva, skin cells, etc.)
2) Polymerase Chain Reaction (PCR) is used to
make millions of copies of specific DNA
segments containing polymorphic regions
3) Capillary electrophoresis separates DNA
fragments by size, with smaller fragments
moving faster
4) Multiple STRs are analysed simultaneously to
create a comprehensive profile
5) The sizes of various paternal/maternal
variants of different STRs are compiled in a
table, creating a unique DNA fingerprint
Applications of DNA Polymorphism
Analysis
DNA polymorphism analysis has numerous
practical applications:
1) Forensic Identification: Matching suspects to
DNA evidence from crime scenes
2) Paternity and Relationship Testing:
Establishing parent-child relationships
3) Disaster Victim Identification: Identifying
remains from disaster sites