A chromosomal disorder, anomaly, aberration, or mutation is a missing, extra, or irregular portion of chromosomal DNA. It can be from a typical number of chromosomes or a structural abnormality in one or more chromosomes. Chromosome mutation was formerly used in a strict sense to mean a change in a chromosomal segment, involving more than one gene. The term "karyotype" refers to the full set of chromosomes from an individual.

1. CHROMOSOMAL
ABERRATION
Prepared by :
INDU SARMA
5th semester , Botany

2. CHROMOSOME
Chromosomes are rod shaped or thread like condensed
chromatin fibres which store and transmit coded hereditary
information.
The structure of
chromosome consist of:
Chromonema
Primary constriction or
centromere
Secondary constriction
Telomere

3. CHROMOSOMAL ABERRATION
Mutations that cause change in the structure or number of
chromosomes are called chromosomal aberration.
These are of two types-
Structural chromosomal aberrations (change in the
structure of gene sequence).
Numerical chromosomal aberrations (change in the
number of chromosome).
Factors responsible for chromosomal aberration are-
Due to error in cell division.
Maternal age and
environment

4. STRUCTURAL CHROMOSOMAL
ABERRATIONS
Structural chromosomal aberration can be divided into four
types-
Deficiency or deletion
Duplication
Inversion
Translocation
Deletion and duplication involve alteration with certain
chromosomal segment being lost or doubled.
Inversion and translocation involve changes in position of
chromosome segment.

5. DELETION OR DEFICIENCY
The loss of a section of genetic material and genetic information
from a chromosome structure.
Deletion was the first structural aberration detected by Bridges
in 1917 on X-chromosome of Drosophila.
Deletion can be of two types-
Terminal deletion- It
involves a single break
near the end of the
chromosome.
Intercalary deletion –
It involves two break in
the middle portion.

6. EFFECTS OF DEFICIENCY
Deficiency is useful in determining exact location of
the gene on the chromosome.
It will show pseudo dominance effect.
Deficiency loop
Formation takes place
during synapsis.
For example, in X-Chromosome of Drosophila, few
bands are missing from the tip of X-band which
result in formation of notches in wing margins in
female fly.

7. DUPLICATION
A structural change resulting in doubling of genes in a section of
a chromosome. It can be intra-chromosomal duplication and
inter-chromosomal duplication.
Duplication can be of four types-
Tandem duplication- The
additional chromosome segment is
located just after the normal
segment, gene sequence being the
same.
Reverse tandem duplication:
Same as above but the gene
sequence of additional segment is
inverted.

8. Displaced duplication-
Here a sequence of
chromosome get displaced in
the same arm (intra arm) or
in different arm (inter arm) of
the chromosome.
Transposed duplication- Here, duplicated gene sequence is
attached to another position owing to inter chromosomal
duplication.

9. EFFECT OF DUPLICATION
Due to supply of additional genetic material and
change genetic balance, they play important role in
evolution at individual and population levels.
For example: The theory of bar eye mutation in
Drosophila is common example of duplication.

10. INVERSION
It is an intra-chromosomal aberration, inversion of a
chromosomal segment take place in intercalary position
rotating at about 180 degree on its axis.
It is of two types-
Paracentric inversion: This
inversion is confined to a single
arm of chromosome and do not
carry centromere.
Pericentric inversion: In this
type of inversion, break points are
located in both arms of
chromosome including
centromere.

11. Effect of inversion:
The location of inverted
segment can be recognised
by the presence of inversion
loop during meiosis.
Supressing of crossing
over.
Possibly the appearance of
mutation owing to position
effect.

12. TRANSLOCATION
Integration of a chromosome segment into a non-
homologous chromosome is known as translocation.
Translocation are of two types:
Non-reciprocal translocation and
Reciprocal translocation
Simple or terminal
translocation: Here,
terminal segment of a
chromosome get
integrated with a
non-homologous
chromosome.

13. Shift translocation or
interstitial translocation: Here,
an intercalary segment of a
chromosome is integrated
with a non-homologous
chromosome.
Reciprocal translocation:
here, two non-homologous
chromosome exchange their
segments. This is the most
common type of translocation.

14. Effect of translocation:
It brings an qualitative change in the chromosome
structure.
It will bring about changes in the sequence of genes in
chromosomes which may eventually produce several
abnormalities in body characters. This is position effect.
The most harmful effect of translocation is semi-sterility it
causes.