This document discusses genetic instability. It defines genetic instability as an increased rate of genomic alterations ranging from point mutations to chromosome rearrangements. It describes three main types: nucleotide instability, microsatellite instability, and chromosomal instability. Causes of genetic instability include replication errors, defects in DNA repair pathways, and issues during cell division. Methods for detecting instability include karyotyping, FISH, and array technologies. Genetic instability is a hallmark of cancer and helps accelerate tumor genesis by increasing mutations. Cells use mechanisms like DNA proofreading and cell cycle checkpoints to maintain stability.

1. M.C.Prabhath
University of Sri
Jayawardenepura
Sri Lanka
4th Year -1st Semester
17.2.2016
1
Genetic Instability

2. Content
2
 Introduction
 Genetic Instability
 Types of Genetic Instability
 Causes of Genetic Instability
 Methods for detection and analysis of genome
instability
 Genome instability and tumor genesis
 Major mechanisms used to maintain genomic
instability
 Discussion
 Summery
 References

3. Introduction
3
 The genome is an organism’s complete set of
DNA and is organized into chromosomes
containing genes that encode for hereditary traits.
 As our cells grow reproduce and die, DNA is
repeatedly replicated and repaired and bits and
pieces of its sequences are changed in the
process, thus producing mutations.
 These mutations create genetic variation and it is
proven that genetic mutation is key to our
evolution and survival.
 But ,mutations are not always beneficial, they can
be harmful leading to genetic diseases.
 When these mutations occur in an increased
levels genetic instability takes place.

4. Genetic Instability
4
 A range of genetic alterations from point
mutations to chromosome rearrangements
- Aguilera and Gonzales,2008
 An increased rate of genomic alteration although
some use the term to describe the state of the
altered cancer genome.
- Kwei et al.,2010
 A variety of DNA alterations, encompassing single
nucleotide to whole chromosome changes.
- Pikor et al., 2013

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 A transient or persistent state that increases the
spontaneous mutation rate, leading to gross
genetics alterations such as rearrangements and
changes in chromosome number.
- Pikor et al., 2013
Commonly ,
 Genetic alterations
 Increased rates
 Nucleotides to Chromosomes

6. Types of Genetic Instability
6
Based on the level of disruption,
1) Nucleotide Instability
2) Microsatellite Instability
3) Chromosomal Instability
- Pikor et al.,
2013

7. 01) Nucleotide Instability
7
 Due to replication errors and impairment of the
base excision repair and nucleotide excision
repair pathways.
 Subtle sequence changes involving only one or
few nucleotides , such as
Substitutions
Deletions
Insertions
 Mitochondrial genome also displays this.

8. Source- Crols classroom blog.genetics8

9. Dissorders associate with NIN
9
Xeroderma pigmentosum
MYH associated polyposis

10. Detection of G>C varient encoding a Gly>Arg amino acid change by
sanger sequencing in two lung cancers.
Source –Pikor et al.,2013
10

11. 02)Microsatellite Instability
11
 Repetitive DNA sequences ,comprising
1-6 bp located throughout the genome.
 Size is highly variable.
 Results from defects in mismatch repair
,specifically alterations of the
MLH1,MSH2,MSH6 and PMS2 genes,
which causes deletions or random
insertions and expansion of
microsatellites and a hyper mutable
phenotypes.

12. Defects in Mismatch repair lead to the expansion or contraction of
microsatellites throughout the genome.
Source-Pikor et al., 2013
12

13. Disorders associate with MIN
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 Gastric,Endometrial,Ovarian,Lung and
Colorectal cancers.
 Lynch syndrome

14. 03)Chromosomal Instability
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 Most prominent form.
 90% of human cancers exhibiting chromosomal
abnormalities and aneuploidy.
 An increase in the rate of gain or loss of segmental
and whole chromosomes during cell divisions.
 CIN tumors are characterized by
Aneuploidy
Amplifications
Deletions
Translocations
Inversions

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- Inversion
-Amplification
- Translocations

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 Also occur because of alterations in,
Mitotic Timing
Mitotic checkpoint control
Microtubule or centrosome dynamics
Double strand break repair
 These alterations lead to karyotypic instability
and growth of tumor populations.

19. Disorders associate with CIN
19
 Breast,prostate .non small cell lung cancer,
leukaemia,Neuroblastoma,Hodgkins and non
Hodgkins lymphoma,Head and Neck cancer.
 Angelmen syndrome,Williams Syndrome , Cri du
chat syndrome.

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21. Causes of genetic instability
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 Replication dysfunction as a major
source of instability .
 Low replication Initiation Density
 Untimely Initiation causing Re-
replication
 Faulty replication fork progression
 S phase checkpoint Dysfunction
 Defective Nucleosome Assembly and
remodeling

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 Failures in post replicative repair and homologous
recombination
 Site specific hotspots
 DNA repeats
 Fragile sites
 Non B DNA structures ,G-Quadruplexes and
Telomeres
 DNA-Protein barriers to replication fork
progression
 Cell physiology and metabolism
 Aging

23. Methods for the detection and
analysis of genome instability
23
 Single cell approach
Karyotyping
Fluorescence insitu Hibridization –Fish
Single cell sequencing
Multiple annealing
Looping based amplification cycles

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 Multi cell approach
Flow cytometry – measures cells in a
suspension as they pass through a laser scatter
light and emit fluorescence can be used to detect
cellular aneuploidy.
Array comparative genomic hybridization-
Offers the ability to quantitatively detect and
visualize whole and segmental chromosomal
alterations .
SNP arrays- enable more precise
mapping of copy number alterations.
PCR-Amplify microsatellite regions and
lengths of tandem repeats.

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28. Genetic Instability and Tumor
genesis
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 Cancer is a genetic disease.
 Tumor cells contain multiple mutations ,ranging
from single nucleotide sequences changes and
numerical alterations of chromosomes.
 Collectively , these mutations are referred to as
genome instability ,which may be predisposed
through inherited ,germline mutations as in the
case of p53,BRCA1,BRCA2 or acquired as
somatic mutations throughout an individuals
lifetime.
-
Chen ,2015

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Acquisition of
some form of
inherent genomic
instability is a
hallmark of tumor
genesis.
- Sieber etal .,
2013

30. Arguments for genomic instability as
the engine of tumor genesis
30
 Tumors harbor too many mutations to be
explained by anything other than underlying
genomic instability.
 The probability of a tumor acquiring enough
mutations for the full, malignant phenotype is too
low unless the cells have an unstable genome.
 Humans and model organisms with inherent
genomic instability are prone to tumors.
 In some tumors , there is direct evidence that
some pathways that are involved in maintaining
genomic integrity are defective.

31. Genetic instability accelerate carcinogenesis.
- Beckmann and Loeb, 201531

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 DNA polymerases and genetic instability-
In mammals it is limited.
Genetic instability in proofreading of
DNApolymerases increases the incidences of
lymphoma and epithelial tumors in mice, so can be
in humans.
 DNA repair enzymes and genetic instability
Xeroderma pigmentosum patients- defect in
nucleotide excision repair pathway

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 Chromosomal instability
Aneuploidy ,gross chromosomal translocations and
molecular loss of heterozygocity without grossly
visible karyotypic changes are common in all type of
tumors.
 Cell cycle checkpoints and genetic instability
The most extensively checkpoint genes p53 and
pRb are among the most frequently mutated in
human cancers.
Other checkpoint genes include the ATM gene,
which is mutated in Ataxia telangiectasia .
There is also evidence that BRCA1,BRCA2 inherited
breast and ovarian cancer .

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Could the clinical
appearance of cancer
be prevented by
decreasing the rate of
genetic change?

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 Cancer typically occurs late in life and
evolves over decades.
 Amodest reduction in the rate of
carcinogenesis could delay the onset of
cancer by decades.
 Enhanced genetic stability could slow
down carcinogenesis in a meaningful
way ,leading to “PREVENTION by
DELAY”.
 Prevention by delay may be particularly
applicable for cancers associated with
prolonged chronic inflammation due to

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 A reduction in the rate of mutation accumulation
by only two fold ,could delay the clinical
appearance of the tumor from age 50 to age 90.
 Compensation of the altered DNA mechanisms or
altered DNA polymerases in promoting genetic
instability would be more challenging with current
technologies , as it might require comprehensive
gene therapy.

37. Role of genetic instability in relation
to therapy
37
 Genetic instability may play a role in the
mechanism of action of chemotherapy.
 Genetic instability not only increases the rate of
acquiring mutations which may be essential for
carcinogenesis,but also accelerates the
acquasition of deleterious mutations which
reduces the fitness of clones potentially leading to
their extinction.

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 Beyond a critical value, further increases in
genetic instability are likely to exceed the
optimum and lead to extinction of clones.
 The majority of chemotherapeutic agents
interfere with aspects of DNA metabolism and
are mutagens.
 If the cancer consists of genetically unstable
cells, further increased mutagenesis due to
chemotherapy could lead to accumulate
deleterious mutations and extinction of
malignant clones.
 Some scientists have suggested that in
addition to directly causing mutations
,chemotherapy may select for genetic

39. Major mechanisms used to maintain
genetic stability
39
 Normal mammalian cells mainly resort
to four mechanisms to maintain their
genomic stability during cell
division.(Shen,2011)
1)High fidelity of DNA replication in S
phase
2)Accurate distribution of chromosomes
among daughter cells during mitosis
3)Error-free repair of sporadic DNA
damage throughout the cell cycle.

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41. 1)High fidelity of DNA replication in S
phase
41
 High fidelity of base pairing and proofreading
activities by DNA polymerases.
 Mismatch repair macinery to correct not only
mismatched bases ,but also secondery DNA
structures resulted from replication slippage.
 Timely resolution of stalled replication forks.
 Maturation of okazaki fragments.
 Replication licensing mechanisms to ensure
that the entire genome is duplicated
completely .
 Coordinated reassembly of chromosomes
from newly synthesized DNA.

42. 2)Accurate distribution of chromosomes
among daughter cells during mitosis
42
During mitosis ,the sister chromatids are equally
distributed in daughter cells .This is mainly
coordinated by many processes.
 Chromosome condensation
 Sister chromatid cohesion
 Centrosome duplication and separation
 Kinetochore assembly and attachment
 Spindle formation and checkpoint
 Chromosome segregation
 Cytokinesis
Deregulation of above processes cause
chromosomal instability.

43. 3)Error-free repair of sporadic DNA damage
throughout the cell cycle.
43
 Throughout the cell cycle ,the genome
encounters various forms of spontaneous and
induced DNA damages.
 These damages are repaired by severel well
defined repair pathways.
 Error prone repair- Completion of some of the
repair processes to fix chemical damages to the
DNA double helix may cause alterations or
rearrangements.
 Error free repair- Fix the damage to the DNA,but
also preserve the original genome structure.

44. 4)Cell cycle progression and
checkpoint control
44
 Cell cycle checkpoints are built to
ensure that progression from one phase
to the next under a condition of
minimum risk of genomic alteration.
 This is accomplished by delaying the
entry into the next phase until the risk
factors are removed.
 Another important function of cell cycle
checkpoint is to effectively trigger some
processes to eliminate the severely

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 The G1/S checkpoint is to restrict damage
cells entering S phase .
 The G2/M checkpoint prevents cells from
premature entry into mitosis.
 The intra S checkpoint helps to delay the
fringe of replication of origins or slows down
DNA duplication during S phase.
 The mitotic spindle checkpoint ensures
normal spindle function in order to minimize
chromosome segregation errors.
 The post mitotic checkpoint can prevent
daughter cells of abnormal mitosis from
entering the next interphase.

46. Discussion
46
 Genetic Instability is a hall mark of cancer.
 Nucleotide instability is the rarest among three
types of genetic instabilities.
 Ionizing radiation, dietary factors, lack of nutrition
will also can be considered as causes of genetic
instability.
 Detection methods of genetic instabilities exhibit
both advantages and disadvantages. Those
techniques must be developed.
 It is an argument .the role of genetic instability in
cancer.

47. Summary
47
 Genetic Instability – Various definitions, but have
common features.
 Three types of genetic Instability.
 Causes of Genome Instability .
 Single cell and multi cell approaches in methods
for the detection and analysis of genomic
instability.
 Genetic Instability as a major reason for cancer.
 Four major mechanisms used to maintain
genomic stability.

48. References
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 Abdel-Rahman, W. M., Katsura, K., Rens, W., Gorman, P.
A.,Sheer, D., Bicknell, D.(2001). ‘Spectral karyotyping suggests
additional subsets of colorectal cancers characterized by pattern
of chromosome rearrangement. Proceedings of the National
Academy of Sciences of the United States of America,98(5),
2538–2543.
 Anderson,G.R.(2001)‘Genomic Instability in Cancer’.Current
Science,18(5):501-507
 Beeckmann,A.R. and Loeb,A.L.(2005) ‘ Genetic onstability in
Cancer:Theory and experiment’.Seminars in Cancer
Biology,15:423-435.
 Aguilera,A.and Gonzales,B.G.(2008) ‘Genomic Instability: a
mechanistic view of its causes and consequences’.Nature,9:204-
217.
 Aguilera,A. and Garcia-Muse,T.(2013) ‘ Causes of Genome
Instability’.Annual Review of Genetics,47:19-50.

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 Charames,G.S. and Bopat,B.(2003) ‘Genomic Instability and
Cancer’.Current Molecular Medicine,3 : 589-596.
 Chen,H.Maxwell,C. Connel,M. (2015) ‘ The Generation,Detection
and Prevention of Genomic Instability During Cancer Prognosis
and Metastasis’.Cancer Metastasis,20:15-26.
 Dworaczek, H., and Xiao, W. (2007). ‘Xeroderma pigmentosum: a
glimpse into nucleotide excision repair, genetic instability, and
cancer’. Critical Reviews in Oncogenesis, 13(2), 159–177.
 Gagos, S., and Irminger-Finger, I. (2005). ‘Chromosome
instability in neoplasia: chaotic roots to continuous growth’. The
International Journal of Biochemistry & Cell Biology, 37(5), 1014–
1033.
 Kwei,K.A. Kung,Y. Salari,K. Holcomb,N.I. Pollock,J.R. (2010)
‘Genomic Instability in breast cancer: Pathogenesis and clinical
impications’.Molecular Biology, 4 : 255-266.
 Leach, F. S., Nicolaides, N. C., Papadopoulos, N., Liu, B., Jen,J.,
Parsons, R., et al. (1993). ‘Mutations of a mutS homolog in
hereditary nonpolyposis colorectal cancer’.Cell, 75(6), 1215–
1225.

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 Lengauer,C. Kizler,K.W. Vogelestein, B.(1998) ‘Genetic
Instabilities in Human cancers’.Nature,396:643-649.
 Muresu, R., Sini, M. C., Cossu, A., Tore, S., Baldinu, P.,
Manca,A.(2002). ‘Chromosomal abnormalities and microsatellite
instability in sporadic endometrial cancer’. European Journal of
Cancer, 38(13), 1802–1809.
 Pikor,L. Thu,K. Vucic,E. Lam,W.(2013) ‘The detection and
implication of genome instability in cancer’.Cancer
Metastasis,32:341-352.
 Rao,C. and Yamada,H.Y.(2013) ‘Genomic Instability and colon
carcinogenesis;from the perspective view of genes’.Frontiers in
Oncology,3:1-13.
 Schvartsman,J.M. Sotillo,R. Benzera,R.(2010) ‘Mitotic
Chromosomal Instability and cancer :Mouse modelling of the
human disease’.Nature.10:102-115.
 Shen,S.(2011) ‘Genomic Instability and Cancer:an
Introduction’.Journal of Molecular Biology,3:1-3.

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 Sieber,M.O. Heinmann,K.Tomlinson,P.M.(2003) ‘Genomic
Instability ,The engine of Tumorigenesis?’.Cancer,3:701-707.
 Tassan, N., Chmiel, N. H., Maynard, J., Fleming, N.,Livingston,
A. L., Williams, G. T.,(2002). Inherited variants of MYH
associated with somatic G:C→T:A mutations in colorectal
tumors. Nature Genetics, 30(2), 227–232.

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