topic- Polymorphism at dna level cytogenetics

1. Polymorphism at DNA Level
By
Sooraj Singh
M.Sc Ag.
Department of Genetics & Plant Breeding
J.V. COLLEGE , BARAUT

2. •History
•Introduction
•Types
•Identification
Contents
•Identification
•Significance
•Application
•Conclusion
•References

3. •Originally defined by Ford in 1940.
•E. B. Ford and his co-workers from(1920-70s) worked on
it.
•Later Cavalli-Sforza & Bodmer defined in 1971.
History
•Occurrence of multiple alleles at one locus in same
population, where at least two alleles occur with
minimum frequency of 1%.

4. Polymorphism
•Combination of Greek words poly (multiple) and
morph (form).
•Multiple forms of a single gene , exists in an
individual or group of individuals.
Introduction
individual or group of individuals.
•Majority are silent , not alter function or expression
of a gene .
•Some polymorphisms are visible.
•e.g dogs E locus, five different alleles
( E, Em, Eg, Eh, e )contribute to pigmentation and
patterns in skin coat of the dog.

5. Types of DNA Polymorphism
Single
Nucleotide Insertion/Deletio
Polymorphic
Structural and
Copy Number
DNA Polymorphism
Nucleotide
Polymorphisms
(SNPs)
Insertion/Deletio
n Polymorphisms
Polymorphic
repetitive
sequences
Copy Number
Variations
(CNVs)
Mini-
satellites
Micro-satellites
Macro-satellites

6. 1. Single Nucleotide
Polymorphisms (SNPs)
The simplest and most common of all
polymorphisms are simple, single base
pair alteration in some individuals at the
same locus
SNPs generally have simply two alleles
conforming to the two dissimilar bases
occupying a particular location in the
genome

7. Types of SNPs:
 Transition
Substitution between purine (A, G) or pyrimidine (C,
T). Constitutes 2/3 of all SNPs.
 Transversion:
Substitution occurs between purine and pyrimidine
Substitution occurs between purine and pyrimidine

8. 2. Insertion /
Deletion
Polymorphism
• The next stage of polymorphism is the result of
variations caused by insertion or deletion
(indels) of between 2 and 100 nucleotides.
•The amount of indels is in the hundreds of
thousands in the genome.
3. Polymorphic
3. Polymorphic
3. Polymorphic
3. Polymorphic
repetitive
repetitive
sequences
sequences
•Can involves as a few as 2 copies are many
thousands copies
•Based on the size of the repeat unit it can be
classified as follows :-
Macrosatellites (Repeats longer than 100bps)
Minisatellites (Repeats usually less than 50 bps long)
Microsatellites (Repeat units less than 10 bps long)

9. 4. Copy Number
Variations (CNVs) 
Involves repetition of
Involves repetition of complete
complete gene
gene
sequence
sequence

 Happens due to duplication or deletion
Happens due to duplication or deletion
events
events

10. •Identified in laboratory using variety of methods.
•RFLP method of DNA typing and
•PCR based DNA sequencing
•Detection of polymorphism by RFLP method ; -
Identification
Restriction Fragment Length Polymorphism
Restriction Fragment Length Polymorphism
Dr. Alec Jeffreys, who observed length polymorphism by treating
DNA sample with restriction enzymes
He then used the molecular sieving method of gel electrophoresis to
isolate DNA pieces as per their sizes

11. After moving the detached DNA pieces from the gel to nylon
membrane
He treated the membrane with a radioactive probe that
binds with a selected repetitive nucleotide sequences
When the nylon sheets were kept contrary to x-ray
sensitive film, the locations of DNA pieces carrying the
radioactive markers observed
radioactive markers observed
Observed as sequences of strokes that bear bar
resemblance to bar codes
These bar codes have two chief potentials: the pattern
varies from person to person, enabling the representation
of an individual’s DNA

12. PCR Tube
Primer
G C
T A
Nucleotides
DNASample
91 -94 °C- Strands Separated 1-Denaturation
2-Annealing
55-65°C - Primer binds to strand
Thermal Cycler PCR Cycle
Taq Polymerase
C
3-Extension
72°C – Synthesis of new strand

13. Clinical Significance
Lungs Cancer
• Polymorphism have been discovered in multiple XPD
exons.
•‘XPD’involvd DNArepair mechanism during DNA
replication
•Two common polymorphism
•Asp312Asn
•Asp312Asn
•Lys751Gln
•Both result in a change of singleAmino acid
Asthma
•Inflammatory disease of lungs
•There are many genes for asthma as, one is CD14
•Cause polymorphism in which increase of CD14
protein with low IGE serum

14. Applications
•Gene Mapping
• Pharmacogenomics.
(I) Pharmacodynamics
(II) Pharmacokinetics
•Forensics.
(I) Crime Scene
(II) Paternity
•Agriculture.
•Biological research.
•Disease Identification.

15. •It Provides opportunity to integrate selection studies
with knowledge about molecular genetics and their
target.
•Polymorphism of gene-regulatory region is one of
major contributors of phenotypic variation between and
within population.
Conclusion
within population.
•Future studies in genetics will determine genes residing
in these phenotypes to map genes functions.

16. References
https://en.wikipedia.org/wiki/Gene_poly
morphism
https://youtu.be/Xe2JOtKJ1A0?si=GkLxuB
a3PV8F-eDI
https://youtu.be/tjarMHwAQqI?si=v-
1UWNqq6_Vu7vUX
https://www.slideshare.net/awaismalik78/
https://www.slideshare.net/awaismalik78/
genetic-polymorphism-238139855