These slides provide you the simplest explanation about structural aberrations in chromosomes with beautiful illustrations.

1. Structural abberetions in chromosomes.
Chromosomal
Abberetions

2. Created by :
Gurunath A.M
B.Sc in Biotechnology
3rd semester

3. Index :
Deletion
Terminal
Interstitial
Duplication
Tandem
Reverse Tandem
Displaced
Translocation
Simple
Isochrome
Reciprocal
Shift
Inversions
Pericentric
paracentric
01
02
03
04

4. Definition.
The chromosomes of each species has characteristic morphology and number.
But, sometimes due to some accidents or irregularities at the time of cell
division, crossing over or fertilization some alterations in morphology and
number of chromosomes takes place.
The changes in the genome involving chromosome parts, whole chromosomes
or whole chromosome sets are called “ Chromosomal aberrations” or
“Chromosomal mutations”. These mutations can be inherited.

5. Structural changes in chromosomes may be of following types :
1. Deletion – Terminal, Interstitial.
2. Duplication – Tandem, reverse tandem & displaced.
3. Translocation – Simple, isochrome, reciprocal, Shift.
4. Inversion – Pericentric & Paracentric.
Types of structural changes in
chromosomes

6. Deletion.
• Portions of chromosome without a centromere (acentric fragments) lag in
anaphase movement and are lost form reorganizing the nuclei or digested
by nucleases.
• Such loss of a portion of chromosome and the genes associated with it is
termed deletion.
• The chromosomes with deleted parts can never revert back to normal
condition.
• If the deletion takes place in allosomes, then the deletion is transmitted to
the next generation as well.
• When a part of chromosome of the dominant allele is deleted, the recessive
allele starts showing dominance, this phenomenon is called
“pseudodominance”.
• There are two type of deletions :
1. Terminal
2. Interstitial

7. 1. Terminal Deletion : This is when a part of the chromosome is deleted at
the terminal end of the chromosome.
It results by only one break in the chromosome.
A B C D E GF
A B C D E GFDeletion -
Aberrated chromosome - A B C ED
Normal chromosome -

8. 2. Interstitial : This type of aberration results when a portion is lost in the
middle of the chromosome.
This is caused by two breaks in the chromosome, one at the starting and
another at the end of the deleted region.
A B C D E GF
A B C
D E
GFDeletion -
Aberrated chromosome -
Normal chromosome -
A B C GF

9. Examples : Cri du chat syndrome
Deletion of some chromosome regions produce their own unique
phenotypes such as “cri du chat” syndrome in human babies.
• Human babies missing a portion of the short arm of chromosome 5
(autosome) have a distinctive cat-like cry, hence the name.
• They are also mentally retarded (IQ below 20), have saddle nose and
exhibit microcephally (small head).
The karyotype of cri du chat patient
is called 5𝒑−

10. Duplication.
• The presence of a part of chromosome in excess of the normal chromosome
is known as duplication. Due to this, even though the chromosome number
is the same, there is extra genetic material.
• These extra genes present in the duplication may cause those genes to not
function properly, these extra instructions leads errors while producing the
phenotype.
There are three major types of duplication :
1. Tandem.
2. Reverse tandem.
3. Displaced.

11. 1. Tandem : In case of tandem duplication the duplicated section of the
chromosome sits right beside the normal chromosome part which it
duplicated form.
Normal -
Duplicated -
A B C D E GF
A B C D E GF D E F

12. 1. Reverse Tandem : In this case the duplicated section of the
chromosome sits right beside the normal chromosome part which it
duplicated form but in a reversed sequence.
Normal -
Duplicated -
A B C D E GF
A B C D E GF F E D

13. 1. Displaced : In Displaced duplication the duplicated section does not
sit adjacent to the section which it duplicated from. Depending on
weather the duplicated portion is on the same side of the centromere as
the section which it duplicated from or on the opposite side, displaced
duplication can be termed either homobranchial or heterobranchial.
Normal -
Homobranchial -
A B C D E GF
A B C D E FF G D E
Homobranchial - A B CD E GF D E F

14. Example : Bar eyed Drosophila.
The bar phenotype of Drosophila is characterized by narrower, oblong, bar
shaped eye with fewer number of facets.
There are few genes which are responsible to give the narrow shape to the
eye of the Drosophila, when the region of the chromosome containing
these genes are duplicates, the expression of genes will become higher
and the eye of the fly becomes narrower, like a bar.

15. Translocation.
• The shifting or transfer of a part of chromosome or setoff genes to a non-
homologous chromosome is called translocation.
• There is no addition or deletion of genes in translocation, only the sequence
and the position of the genes are altered.
• There are four types of translocation :
1. Simple.
2. Isochrome.
3. Reciprocal.
4. Shift.

16. 7
1. Simple Translocation: When a terminal segment of the chromosome
breaks and re-attaches to one end of a non-homologous chromosome then
it is called simple translocation.
A B C D E GF
G
A B C D E
F1 2 3 4 5 6
Aberrated chromosome -
Non-homologous
chromosomes -
1 2 3 4 5 76

17. 2. Isochrome Translocation : This type of translocation is caused by
the simultaneous deletion and duplication of chromosome parts. In this
type of abnormality the chromosomes arms are mirror images if each other.
This type of chromosome is also called isochromosome.
Aberrated chromosome -
Normal chromosome - A B C D E HF G
A B C D D AC B

18. 3. Reciprocal Translocation : In this type of translocation a segment of one
chromosome is exchanged with a segment from another non-homologous
chromosome. Hence, two translocations are simultaneously achieved.
A B C D E GF
GF1 2 3 4 5
7A B C D E 6
Aberrated chromosome -
Normal chromosomes -
1 2 3 4 5 76

19. 4. Shift Translocation : In this type of translocation an intercalary part
of one chromosome breaks and gets itself inserted into intercalary
position of a non-homologous chromosome.
A B C D E GF
GA B C D
1 2 3 4 5 7FE 6
Aberrated chromosome -
Normal chromosomes -
1 2 3 4 5 76

20. Inversion.
• This type of chromosomal aberration involves rotation of a part of a
chromosome by 1800
on its own axis.
• Just like in translocation, there is no addition or deletion of genes but simply
a re-arrangement of the gene sequence.
• It takes place in a intercalary position.
• The location of the inverted segment can be detected in meiotic nuclei by
the presence of an inversion loop.
• Accordingly there are two types of inversion :
1. Pericentric
2. Paracentric

21. 1. Paracentric Inversion : In this type of inversion the segment involved is
present wholly within one chromosome, that means no centromere is
involved.
Normal - A B C D E HF G
Paracentric inversion-
A B C D H
EFG
Aberrated chromosome -
A B C D H
EFG
G

22. 2. Pericentric Inversion : In this type of inversion the break points are
located on both the arms of the chromosome are involved including the
centromere.
Normal - A B C D E HF G
A B E HF
CD
GPericentric inversion -
A B E HF
CD
GAberrated chromosome -

23. Dr. P.S Verma, Dr. V.K Agarwal
Cell biology.
Bibliography.

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