chromosomal abberation

2. • Numerical - change in no.
• Structural – change in structure
Chromosomal
aberrations
Types

3. There are 2 basic types of
Chromosome Abnormalities
1. change in the structure of chromosomes
(structural abnormality)
2. change in the number of chromosomes
(numerical abnormality)
Numerical and Structural Abnormality are
not mutually exclusive, they may be
present at the same time.

5. Numerical Abnormality• Euploidy
An exact multiple of the haploid chromosome
complement.
 Monoploidy (N) - having one set of basic
chromosomes
 Diploidy (2N) - having two set of basic
chromosomes
 Polyploidy - Autoploid
Alloploid

6. Polyploidy
• An individual having more than two basic or
monoploids sets of chromosomes
Autopolyploids are two types :-
1. Autopolyploids – polyploids which originates
by multiplication of the chromosomes of a single
species.
a. Autotriploids – banana, apple, sugerbeet,
watermelon
b. Autotetraploids – rye, grapes, alfalfa

7. 2. Allopolyploids – polyploids which originates
by combining complete chromosome sets from
two or more species.
a. Natural alloploids – wheat, cotton, tobacco,
mustard, oats, brassica
b. artificial alloploids – raphanobrassica ,
triticale, cotton, wheat, mung- urid

8. Aneuploidy
The variation involves addition or deletion
of one or more chromosomes, but not in the
complete set.
aneuploidy is of two types :-
1.Hypoploidy
2. Hyperploidy

9. a. Monosomy (2N-1)
• lacking one chromosomes from a diploid set
• Double monosomics – lack of one chromosomes
each from two different pairs (2N-1-1)
1. Hypoploidy – having chromosomes
less than disomoc condition(2N)
b. Nullisomy (2N-2)
• lacking one pair of chromosomes from a
diploid set

10. a. Trisomy(2N+1)
• Addition of one chrosomes to one pair in
diploid set
• It is may be of two types
I. Simple trisomics – increase in chrmosomes
number is in one pair only (3N+1)
Simple trisomics is of three types viz.
 Primary trisomics – the additional
chromosomes is normal one
2. Hyperploidy- having chromosomes
than disomic condition(2N)

11.  secondary trisomics – additional
chromosomes as isochrosomes
(isochromosomes originate by vertical
division of centromere)
 Tertiary trisomics – additional
chromosomes is isolated one
II. Double trisomics – addition of one
chromosomes in two different pairs
(2N+1+1)

12. b. Tetrasomy(2N+2)
• addition of two chromosomes to one pair or
two different pairs
 simple tetrasomics – addition of two
chrosomes to one pair
 double tetrasomics – two chromosomes are
added each to two different pairs

13. Structural abnormalities
• Rearrangement because of chromosomes
Breakage & subsequent reunion in a different
configuration
• Balanced – chromosomes Complement is
complete
• Unbalanced – when there is incorrect amount
of genetic material

14. Types of Structural
abnormalities
1. Translocations – reciprocal or
robertsonian
2. Deletions
3. Duplication
4. Inversions – paracentric or pericentric
5. Ring chromosomes

15. Translocation
• One way or reciprocal transfer of segments between non
homologous chromosomes .
• It is of three types
1. Simple – when a segment from one chromosome is
transferred and attached to the end of a non homologous
chromosomes
2. shift – transfer of an intercalary segment from one
chromosomes to the intercalary position in a non
homologous chromosomes
3. reciprocal – mutual exchange of segments
between non homologous chromosomes

16. Robertsonian translocation
• Breakage of 2
acrocentric
chromosomes near
centromeres & fusion
of long arms
• Short arms lost – no
importance they
contain genes for rRNA

17. Deletions
• Loss of a portion or segment of chromosomes
• Also known as deficiancy
1. Terminal deletion – loss of either terminal
segment of a chromosomes
a. Heterozygous
b. Homozygous
2. Interstitial deletion – loss of a segment of
chromosomes from the intermediate portion
or between telomere and centromere

18. Duplication
• refers to the occurrence of a segment twice in
the same chromosomes
1. Tandem – in this case sequence of genes in
the duplicated segment is similar to the
sequence of genes in the original segment of
a chromosomes
2. Reverse tandem – the sequence of genes in
the duplicated segment is reverse to the
sequence of genes in the original segment of
a chromosomes

20. Inversion
• A Segment is
oriented in a
reverse positon
1. Pericentric – when
centromere is
involved
2. Paracentric – only
one arm is involved

21. Ring chromosomes
• Break occurs in
each arm & the
2 sticky ends
join
• Distal fragments
are lost