A gene is a segment of DNA that codes for a protein. Chromosomes are composed of sequences of genes. Mutations are changes in DNA that result in phenotypic changes. Mutations can be spontaneous or induced by mutagens like radiation or chemicals. There are different types of mutations, including gene mutations like transitions, transversions, and frameshifts, as well as chromosome mutations like deletions, duplications, inversions, and translocations. Mutation breeding is a plant breeding technique that uses induced mutations to generate genetic variation for crop improvement.

2. Gene:
A gene is a segment of
the DNA molecule
that codes for the
production of a
protein.
Chromosome:
A chromosome is a
structure that is
composed of a
sequence of genes.

3. Mutation:
Mutation refer to sudden
heritable change in the phenotype
of an individual. (A mutation is a
change in the nucleotide sequence
of the DNA molecule.)
Somatic mutations affect only the
individual in which they arise.
Germ cell mutations alter
gametes, affecting the next
generation.
The effect of mutation depends
on both the type mutation and its
location .
Importance of mutation:
The mutation is the main source
of all genetic variations and
because it

4. 1- Nature (Spontaneous) Mutation
2- Artificially (Induced) Mutation

5. Most mutations are spontaneous, rather than
induced by a mutagen
Spontaneous mutations result from DNA replication
errors
The cause of a spontaneous mutation is unknown.
The spontaneous mutation rate in eukaryotes is
between 10-4-to-10-6 per gene per generation

6.  An induced mutation is brought about by a
mutagen.
 A mutagen is a physical agent or a chemical agent
that causes an alteration of the base sequence of the
DNA molecule.

7.  Physical mutagens
 heat
 ultraviolet radiation
 X-ray
 Gama ray
 Alpha and Beta particles
 Chemical mutagens
 Alkylating agents
 benzpyrenes
 aflatoxin
 Base analogues

8.  Ultraviolet radiation causes the formation of
thymine dimers.
 Thymine dimers block DNA replication.
 Cell excises (cuts out) the thymine dimers
using enzymes and repairs the damage.
 A mutation occurs when the repair is faulty

10. 1- Gene mutation
2- chromosome mutation

11. Types of Gene Mutations
a. Transitions convert a purine-pyrimidine
pair to the other
purine-pyrimidine pair (e.g.,
AT to GC or TA to CG).
b. Transversions convert a
purine-pyrimidine pair to a
pyrimidine-purine pair (e.g.,
AT to TA, or AT to CG).
c. Missense mutations have a
base-pair change resulting in
a different mRNA codon, and
therefore a different amino
acid in the protein.
d. Nonsense mutations change a
codon in the ORF to a stop
(nonsense) codon, resulting
in premature termination of
translation, and a truncated
(often nonfunctional) protein

12. E. Neutral mutations change a codon in
the ORF, but the resulting amino acid
substitution produces no detectable
change in the function of the protein
(e.g., AAA to AGA substitutes arginine
for lysine. The amino acids have similar
properties, so the protein’s function may
not be altered).
F. Silent mutations occur when the
mutant codon encodes the same amino
acid as the wild-type gene, so that no
change occurs in the protein produced
(e.g., AAA and AAG both encode lysine,
so this transition would be silent).
G. Frameshift mutations result from
insertions or deletions when the number
of affected base pairs is not divisible by
three.

14.  Variations in chromosome structure or number can
arise spontaneously or be induced by chemicals or
radiation. Chromosomal mutation.
 All chromosome structure mutations begin with a
break in the DNA, leaving ends that are not
protected by telomeres, but are “sticky” and may
adhere to other broken ends.
 Mutations involving changes in chromosome
structure occur in four common types:
a. Deletions.
b. Duplications.
b. Inversions
d. Translocations

15. 1-Deletion
In a deletion, part of a chromosome
is missing. Deletions do not revert,
because the DNA is missing.
Deletion of the centromere results
in an acentric chromosome that is
lost, usually with serious or lethal
consequences. (No known living
human has an entire autosome
deleted from the genome.)

16. 2-Duplication
Duplications result from doubling
of chromosomal segments, and
occur in a range of sizes and
locations.
a. Tandem duplications are
adjacent to each other.
b. Reverse tandem duplications
result in genes arranged in the
opposite order of the original.
c. Tandem duplication at the
end of a chromosome is a
terminal tandem duplication

17. 3-Inversion
Inversion results when a
chromosome segment excises
and reintegrates oriented 1800
from the original orientation.
There are two types.
a. Pericentric inversions
include the centromere.
b. Paracentric inversions do
not include the centromere.
Inversions generally do not
result in lost DNA, but
phenotypes can arise if the
breakpoints are in genes or
regulatory regions.

18. 4- Translocation
A change in location of a
chromosome segment is a
translocation. No DNA is lost
or gained. Simple
translocations are of two types.
a. Intrachromosomal, with a
change of position within the
same chromosome.
b. Interchromosomal, with
transfer of the segment to a
nonhomologous chromosome.
i. If a segment is transferred
from one chromosome to
another, it is nonreciprocal.
ii. If segments are exchanged, it
is reciprocal.
Gamete formation is affected
by translocations.

19.  mutation is one of the special methods of crop
movement.
 Mutation breeding is commonly used in self
pollination and asexually propagated species.
 mutation breeding is rarely used for genetic
improvement of cross pollination species.
 mutation breeding will be rewarding under
following situations(Chopra and Sharma, 1985)

20. 1) When a high yielding variety has oligogenic defect such as
susceptibility to disease, mutation breeding is the best
source of a line for breeder.
2) When there is a tight linkage between desirable and
undesirable characters mutation breeding is the best way of
overcoming such problems.
3) When in fruit crops, the improvement has to be made
without change in the taste and colour of the fruit it can
best be achieved through mutation breeding.
4) In those species where generation cycle is very long, such
as fruit trees and forest trees, mutation breeding is the only
short cut method.

21. Mutation breeding
1. One genotype or variety sufficient.
2. Crossing is not involved.
3. It comes under special method of
plant breeding.
4. It takes lesser time for release of a
new variety.
5. Required mutagenic treatment .
6. It required more skill in handing
mutagens and treated material.
Hybridization breeding
1. Minimum two genetically different
genotypes are required.
2. Crossing is involved.
3. It comes under general method of
plant breeding.
4. It takes 14-15 years for release of a
new variety.
5. non Required mutagenic treatment.
6. It required less skill in handing
materials

22. Question
If you wanted to
change the one
character any way
(type) you will be
choosing
1- gene mutation
2- chromosome
mutation