detailed description of chromosomal abnormalities is provided

1. VAISHNAVI SAXENA
M.Sc. Pre. Zoology

2. Contents of Presentation
1. What is chromosomes ?
2. Introduction of Chromosomal aberration
3. Structural chromosomal aberration
4. Types of Structural chromosomal aberration
5. Numerical Chromosomal aberration and their

3. ?
Tiny thread like structures
Font in the nucleus of most living cell
Carriers of genetic information in the form
of genes
Made up of protein (Histone) and DNA
Each Human normally has 23 pairs of
chromosomes, 46 in number

4. Discovery of Chromosomes
Chromosomes where first described by the Strausberger
in 1875.
The term “Chromosome”, however first used by
Waldeyer in 1888.
They were given the name Chromosome (chromo =
Colour; Soma = body).

5. Chromosomal
Aberrations
 A chromosomal aberration, disorder, anomaly,
abnormality, or mutation is missing, extra or irregular
portion of chromosomal DNA.
OR
 Mutation that cause changes in the structure or
number of chromosomes are called chromosomal
aberrations.
 Generally, the incidence of chromosomes
abnormalities is 5 – 6 persons/1000.
 Many children with a chromosomal abnormalities have
mental or physical birth defects.

6. CHROMOSOMAL ABERRATION
• CHROMOSOMES CONTAINS A NUMBER OF GENES ON THEM. THE NUMBER
AND ALSO THE POSITION OF GENES ON A CHROMOSOME ARE FIXED. THE
CHROMOSOME MAY UNDER GO SOME CHANGES IN STRUCTURE AND NUMBER
DUE TO OF FACTORS.
• THIS CHROMOSOMAL ABERRATION CAN BE CLASSIFIED AS STRUCTURAL
CHANGES AND NUMERICAL CHANGES OF CHROMOSOMES.
• VARIATION IN CHROMOSOMAL STRUCTURE OR NUMBER IS CALLED
CHROMOSOMAL ABERRATION.

7. STRUCTURAL
CHROMOSOMAL
ABERRATIONS
 The mutation and changes that
occur in structure of
chromosomes are structural
aberrations.
 Also known as Chromosomes
Rearragement.
 Sequence of Genes
 Kinds of Genes in
Chromosomes
 Number of Genes

8. Structural
chromosomal
aberrations

 Structural changes are very few in nature
and this can be frequently produced by ionizing
radiation like X – Rays, atomic radiations and by
chemical mutagens. Example :- Mustard Gas.


9. Chromosomal Aberration due to structural
changes can be of Four types
 Changes in the number of Genes
1. Deletions or Deficiencies
o Terminal Deletion
o Intercalary
2. Duplication
o Tendum Duplication
o Duplication on same arm but displaced
o Duplication on different arm
o Reverse Repeat Duplication
 Changes in the location of Genes
3. Inversion
o Pericentric Inversion ( include centromere)
o Paracentric Inversion ( does not include centromere)
4. Translocation
o Reciprocal
o Robertsonian Translocation
5. Ring Chromosome
6. Isochromosome

10. DELETION OR
DEFICIENCIES :-
• The loss of segment of Chromosome is called deletion.
• The deletion can be of two types there are as follows :-
• Terminal Deletions and Intercalary Deletions.
• Terminal Deletion :- When the deletion is occur near the
end of the chromosome than it is called Terminal Deletion.
• Intercalary Deletion :- When the deletion is occurs
middle part of the chromosome than it is called Intercalary
deletion.
•

11. EXAMPLES :-
 Pseudodominance
 Haploid insufficiency

12. Duplication :-
 In duplication a part of chromosome is added
to normal chromosome i.e a part of chromosome
is duplicated in duplication the chromosomal
material is extra in the cell. The duplication can
be of many type. In tendum duplication the extra
part is repeated just after its normal position. In
reverse tendom duplication there is reverse of
duplicated segment. In displaced duplication the
extra segment is some distance away from its
normal location.
 Example :- Bar eyes in drosophila

13. INVERSION
• In inversion a part of chromosome is rearranged in a reveres
order. In inversion the chromosome break at two points, the
broken segment rotates to 180 degree, the rotated part reunits
reversing the gene sequence
• Types of Inversion are :-
• pericentric Inversion (include centromere)
• Paracentric Inversion (Does not include Centromere)

14. Translocation
• The translocation is interchromosomal or
intrachromosomal rearrangement by exchange
of chromosomal segment.
• Types of Translocation are :-
• Reciprocal translocation :- In a reciprocal
translocation two different chromosome
have exchange segment with each other.
• Robertsonian translocation :- In a
Robertsonian translocation an entire
chromosome attach to another at the
centromere.

15. RING
CHROMOSOME
AND
ISOCHROMOSOME
 Ring Chromosome :-
 Ring chromosome usually result from two
terminal breaks in both chromosome arms, followed by
fusion of the broken ends,or from the union of one broken
chromosome end with the opposite telomere region, leading
to the loss of genetic material.

 Isochromosome :-
 formed by the mirror image copy of the
chromosome segment including the centromere.

17. NUMERICAL
CHROMOSOM
AL
ABERRATION
Aneuploidy :- Change in number of individual chromosome, but
not in complete set
OR
It involve the additions or deletion of one or more
chromosomes.
Types of Aneuploidy :-
1. Hyperploidy :- Having chromosome more than disomic
condition 2n
a. Trisomy (2n + 1) :- “Addition of one chromosome to one
pair in diploid set”
b. Tetrasomy (2n + 2):- “Addition of two chromosome to one
pair or two different pairs “
2. Hypoploidy :- Having chromosome less than disomic
condition
a. Monosomy (2n - 1) :- “Lacking one chromosome from a
diploid set. ”
Normal diploid = 2n AABBCC
Monosomic = 2n – 1 AABBC
b. Nullisomy (2n - 2) :- “Lacking one pair of chromosomes

19. Aneuploidy
condition
in human

20. Trisomy 21
PICTURE OF TRISOMY 21

21. Trisomy 13
Trisomy 18
PIRCTURE OF TRISOMY 13 AND 18

22. 2. Euploidy :- “When there is addition or subtraction of one or more sets of
chromosomes ”
a. Monoploidy (n) :- “Monoploidy have half the number of chromosome. Gametes are
example of monoploidy” Example :- Drone of honey bee.
b. Diploidy (2n) :- “The organisms with two sets of chromosomes”. It is denoted by
“2n”. Examples :- Most plats and nearly all animals.
c. Polyploidy (3n,4n,5n) :- “The organisms having more than two sets off
chromosomes”. Polyploidy is specially common in plants.
Types :-
I. Triploid (3n) :- “An organisms with three sets of chromosome”.
II. Tetraploid (4n) :- “An organism with four sets of chromosomes”