The document discusses chromosomal aberrations, which are mutations that alter the structure or number of chromosomes, classified into structural and numerical types. Structural aberrations include deletion, duplication, inversion, and translocation, each with distinct effects on genetic material and implications for evolution. Factors contributing to these aberrations include cell division errors, maternal age, and environmental influences.

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.