Chromosomal aberrations

Includes information regarding structural changes in chromosomes

1. Chromosomal Aberrations
Dr. A. S. Wabale
Assistant Professor and Research Guide
Post Graduate Department of Botany and Research Centre,
Padmashri Vikhe Patil College of Arts, Science and
Commerce, Pravaranagar- 413 713
[email protected]

2. CONTENTS
Types of structuralchanges in chromosomes
A) Deletion:types, cytology and geneticeffects
B) Duplication: types and cytology, position effect and bar eye phenotype in Drosophila
C) Inversion:types and theircytology,
D) Translocation:types and translocationcomplexes
E) Variation in chromosome morphology: Isochromosomes, ring chromosomes and
Robertsoniantranslocation
April 8, 2021 Dr. A. S. Wabale

3. CHROMOSOMAL ABERRATIONS
PERICENTRIC PARACENTRIC
TRANSLOCATIONDELETION
TERMINAL INTERCALARY
SIMPLE
TRANSLOCATION
AFFECT NUMBER OF GENES AFFECT ARRAGEMENT OF GENES
TANDEM
REVERSE
TANDEM
DISPLACED
DUPLICATION INVERSION
RECIPROCAL
TRANSLOCATION
MULTIPLE
TRANSLOCATION
SHIFT
TRANSLOCATION
April 8, 2021 Dr. A. S. Wabale

4. Chromosomal Aberrations: DELETION
Deletion or deficiencyis a condition in which a
small portion of the chromosome is lost resulting
in change in the number of genes of that
chromosome.Mainly it is of two types
1. Terminal Deletion:A condition in which the
terminalpartofthe chromosomeislost
2. Intercalary or Interstitial Deletion:A condition
in which the two break occurs on the
chromosome and the part between such
breaks is lost, followed by joining of the
remaining parts
Cytological detection of deletion:It may be
detected during meiotic prophase. At the time of
synapsis (pairing) a loop is developed on the
normal chromosome so as to pair with the
chromosome in which deletion had occurred.
Deleted
portion
New Resulted
Chromosome
Break occurring
Normal
Chromosome
Terminal
Deletion
Normal
Chromosome
New Resulted
Chromosome
Deleted
portion
Break occurring
Intercalary
Deletion ABCDEFGH
ABCFGH
Normal Chromosome
Deleted Chromosome
Pairing
Deleted Chromosome
ABC FGH
D E
Normal Chromosome
ABC FGH
April 8, 2021 Dr. A. S. Wabale

5. Chromosomal Aberrations: DUPLICATION
Duplicationis a condition in which a small portion
of the chromosome is added resulting in change
in the number of genes of that chromosome.
Mainly it is of twotypes
1. Tandem Duplication:A condition in which
new segment is just located after the normal
one with same gene sequence
2. Reverse Tandem Duplication:A condition in
which new segment is just located after the
normalone with reverse gene sequence
3. Displaced Duplication:A condition in which
new segment is located on the same
chromosome but away from the normal
segment
Normal
Chromosome
Tandem
Duplication
Reverse
Tandem
Duplication
Displaced
Duplication
Cytological detection of duplication:It may be detected during meiotic prophase. At the
time of synapsis (pairing) a loop is developed on the duplicated chromosome so as to pair
withthe normalchromosome
ABCD CDE F G
Duplicated Chromosome
Normal Chromosome
Pairing
Normal Chromosome
ABCD EFG
C D
Duplicated Chromosome
ABCD EFGABCDEFG
April 8, 2021 Dr. A. S. Wabale

6. Chromosome
Structure
Phenotype
X-16A
X-16A
Normal Eye Female
X-16A-16A
X-16A
Bar Eye Female
X-16A-16A
X-16A-16A
Bar eye female (more restricted, 68
facets)
X-16A-16A-16A
X-16A
Double bar eye female (45 facets)
X-16A-16A-16A
X-16A-16A-16A
Double bar eye female (further
reduced)
One phenotype that has been analyzed in Drosophila with
respect to duplications is bar eye. The eye of the fly is
normally an elongated oval shape whereas the bar eye
phenotype is much thinner. When the chromosomes of
males with bar eye are analyzed, a duplication in region 16A
of the chromosome is detected. Another mutant of the eye
shape is the double bar eye. These individuals have a second
duplication of the same 16A region.
The chromosomal environment can have an effect on the
expression of a specific gene. i.e. the phenotype of a gene is
altered by changes in the position or chromosomal
environment of the gene. Such an effect is termed as
Position Effect
Wild Type
(779 facets)
Homozygous Bar
(68 facets)
Homozygous
Double Bar
(25 facets)
Position effect and bar eye phenotype in Drosophila
April 8, 2021 Dr. A. S. Wabale

7. Chromosomal Aberrations: INVERSION
A event in which two breaks occur in a chromosome, the region between these breaks
rotates at 180 degrees and rejoins with the two end fragments refers toInversion.Unlike
deletions and duplications, inversions do not change the overall amount of the genetic
material, so inversions are generally viable and show no particular abnormalities at the
phenotypic level.
Depending upon the involvement of centromere, inversion is of two types:
1.If the centromere is outside the inversion, then the inversion is said tobeparacentric
2.If the centromere is within inverted part then the inversion is said to bepericentric
PARACENTRIC
INVERSION
PERICENTRIC
INVERSION
April 8, 2021 Dr. A. S. Wabale
https://www.youtube.com/watch?v=QXU7XojaEOs

8. CYTOLOGY OF PERICENTRIC AND PARACENTRIC INVERSION
April 8, 2021 Dr. A. S. Wabale

9. TRANSLOCATION
April 8, 2021 Dr. A. S. Wabale
Translocation is a type of chromosomal abnormality in which a chromosome breaks and a portion of it
reattaches to a different chromosome. Chromosomal translocations can be detected by analyzing
karyotypes of the affected cells. Translocations may originate spontaneously. They may be induced by
mutagens, viz., ionizing radiations and many chemical mutagens, since they induce chromosome
breakage. Translocations may be induced by growing plants in calcium-deficient media, as reported by
Nilan and Phillips in 1957.

10. Translocation may be classified on the basis of the trans-located segment being present in the same,
homologous or non-homologous chromosome and the number of breaks involved in the
translocation.
1. Simple Translocation:In this a broken chromosome segment reattaches to another chromosome
of the same homologous pair. It is also known as nonreciprocal or intrachromosomal
translocation.
2. Shift Translocation:In this a broken chromosome segment reattaches to another chromosome of
non-homologouspair. It is also known as nonreciprocal or interchromosomal translocation.
3. Reciprocal Translocation:In this type of translocation breaks occurs on two non-homologous
chromosomes and the broken segments are interchanged and reattached
Simple or
Intrachromosomal
Translocation
Shift or
Interchromosomal
Translocation
Reciprocal
Translocation
TYPES OF TRANSLOCATION
April 8, 2021 Dr. A. S. Wabale

11. MULTIPLE TRANSLOCATION IN RHEO DISCOLOR (2n=12)
April 8, 2021 Dr. A. S. Wabale
A BC DE FG HI JK L
A ‘ B’C ‘ D’E ‘ F’G‘ H’I ‘ J’K ‘ L’
A BC DE FG HI JK L
A ‘ B’C ‘ D’E ‘ F’G‘ H’I ‘ J’K ‘ L’
Multiple Translocation
New Combinations
A LC BE DG FI HK J
A ‘ B’C ‘ D’E ‘ F’G‘ H’I ‘ J’K ‘ L’
The translocation in which two or more
than two pairs of non-homologous
chromosomes are involved refers to
multiple translocation. This can be
explained withRheo discolorwith
chromosome number 2n=12.
There are several different genetic factor
complexes which are combined in the
various species. These complexes
segregates as wholes in meiosis, each
gamete carrying one or other referred as
Renner complexes, a phenomenon named
after its discoverer Renner, in 1914.
The meiocytes ofRheoat diakinesis of
meiotic prophase-I show multivalent rings
and chains comprising of four, six, eight or
all twelve chromosomes. This is because, if
the arm of one of the translocated
chromosome is involved in a second
interchange with third non-homologous
chromosome, a ring of chain of 6 would
form at metaphase

12. A L
L’
K’
K
J
J ’
I ’
I
H
H ‘
G ’
G F
F ‘
E ‘
E
D
D ’
C ’
C
B
B ‘
A ‘
Pachytene stage
MULTIPLE TRANSLOCATION IN RHEO DISCOLOR (2n=12)
April 8, 2021 Dr. A. S. Wabale
Multivalent Ring of
12 Chromosomes
Diakinesis stage
A
L
L’
K’
K
J
J ’
I ’
I
H
H ‘
G ’
G F
F ‘
E ‘
E
D
D ’
C ’
C
B
B ‘
A ‘
Multivalent Chain of
12 Chromosomes

13. Anisochromosomeis an unbalanced structural abnormality in which the arms of
the chromosome are mirror images of each other. The chromosome consists of two copies of
either the long (q) arm or the short (p) arm because isochromosome formation is equivalent to a
simultaneous duplication and deletion of genetic material. Consequently, there is partial trisomy of
the genes present in the isochromosome and partial monosomy of the genes in the lost arm.
ISOCHROMOSOME
April 8, 2021 Dr. A. S. Wabale

14. Robertsonian translocation(ROB) is a chromosomal abnormality where a certain type of a chromosome becomes
attached to another. It is the most common form of chromosomal translocation in humans, affecting 1 out of every 1,000
babies born. It does not usually cause health difficulties, but can in some cases result in genetic disorders such as Down
syndrome and Patau syndrome. Robertsonian translocations result in a reduction in the number of chromosomes.
Robertsonian translocations are named after the American zoologist and cytogeneticistWilliam Rees Brebner
Robertson (1881–1941)who first described a Robertsonian translocation in grasshoppers in 1916. They are also
calledwhole-arm translocationsorcentric-fusion translocations. A Robertsonian translocation effects acrocentric
chromosomes. In an acrocentric chromosome, the narrow region where both halves of the chromosome join is near the
very end of the chromosome. In a Robertsonian translocation, acrocentric chromosomes fuse together. This fusing joins
two “long arms” of DNA into one. As cells multiply, this DNA error is copied over and over, and usually the short arms of
the DNA chain are lost. The lost information can result in your DNA appearing one full chromosome short of the normal
count of 46.
The acrocentric chromosomes in this DNA chain are chromosomes
13, 14, 15, 21, and 22. Common translocation formations include:
1. Chromosome 13 with chromosome 14 (the most common
Robertsoniantranslocationandthemostcommon
chromosome rearrangement found in humans)
2. Chromosome 14 with chromosome 21
3. Chromosome 15 with chromosome 21
4. Chromosome 21 with chromosome 22
Since DNA chromosomes are linked together into 23 pairs, having an
odd number of chromosomes can sometimes indicate that essential
genetic information is missing from your DNA. A Robertsonian
translocation can also result in an extra copy of one chromosome
being included in your DNA. A DNA chain with missing or extra
genetic information is referred to as imbalanced.
Multiple miscarriages, difficulty getting pregnant, and pregnancies in
which the fetus develops a trisomy or other genetic abnormality
could be a sign that has this translocation.
https://www.youtube.com/watch?v=vbGw4VanNjk
Robertsonian
Translocation
Normal
non-homologous
acrocentric
chromosomes
ROBERTSONIAN TRANSLOCATION
April 8, 2021 Dr. A. S. Wabale

15. ASSIGNMENT
April 8, 2021 Dr. A. S. Wabale
Que.1) Explain Chromosomal Aberration / Structural changes in chromosomes in brief
Que.2) Explain deletion, its types, cytological detection y and genetic effects
Que.3) Explain duplication, its types, cytological detection y and genetic effects
Que.4) Explain inversion and its types
Que.5) Explain pericentric inversion in detail
Que.6) Explain paracentric inversion in detail
Que.7) Explain translocation and its types
Que.8) Explain multiple translocation inRhoe discolor
Que.9) Comment on Robertsonian translocation
Que.10) Comment on Isochromosome