Mutations -types, causes and uses

1. Alterations in the basic unit of inheritance and inheritance
patterns.
Prof. Yogesh Sharma
Department of Botany
GDC Akhnoor
Mutations-types, sources (spontaneous and induced), uses and mechanisms of
induction.

2. Mutation
Introduction:
Sudden change in genetic material or character of an
organism is known as mutation.
Individuals showing these changes are known as mutants.
A mutation occurs when a DNA gene is changed or
damaged in such a way as to alter the genetic message
carried by that gene.
An individual showing an altered phenotype due to
mutation are known as variant.
Factor or agents causing mutation are known as mutagens.

3. A mutagen is an agent of substance that can bring about
a permanent alteration to the physical composition of a
DNA gene such that the genetic message is changed.
Mutation which causes change in base sequence of a gene
are known as gene mutation or point mutation
The gene mutations are the only source of new genetic
variability, and without them evolution could not progress
for a long time.
Mutant gene do not become expressed immediately
because most of them are recessive.

4. History
Seth Wright recorded case of mutation first time in 1791
in male lamb with unusual short legs (Ancon breed).
1901- Hugo deVries first used the term mutation to
describe the sudden heritable phenotypic change in
evening primrose Oenothera lamarckiana.
Systematic study of mutation was started in 1910 when
Morgan genetically analyzed white eye mutant of
Drosophila.
H . J. Muller performed induced mutation in Drosophila
by using X-rays in 1927; he was awarded with Nobel
prize in 1946.

5. KINDS OF MUTATIONS
• There exists a lot of controversy about the
possible kinds of mutations among
geneticists.
• They have been classified variously according
to different Criteria.

6. • Classification of Mutation
According to Type of Cell
1. Somatic mutations.
2. Gametic mutations.
• Classification of Mutations
According to the Size and Quality
1. Point mutation:- Deletion,
Insertion/addition,substitution
mutations.
2. Multiple mutations or gross
mutations-Translocation &
Inversion.
• Classification of Mutation
According to the Origin
1. Spontaneous Mutations
2. Induced Mutations.

7. • Classification of Mutation According to the Direction
1. Forward mutations.
2. Back/Reverse mutations
• Classification of Mutation According to Magnitude of Phenotypic
Effect
1. Dominant mutations
2. Recessive mutations
3. Isoalleles
4. Lethal mutations

8. • Classification of Mutation
According to Consequent Change
in Amino Acid Sequence
1. Missense mutations
2. Nonsense or chain termination
mutations
3. Silent mutations
• Classification of Mutation
According to the Types of
Chromosomes
1. Autosomal mutations
2. Sex chromosomes mutations

9. Spontaneous Mutation
• Spontaneous mutation occur frequently in nature without
any cause.
• During the study heredity since1900, Spontaneous
mutation have been recognized in a large number of
organisms.
• Various species of Drosophila have contributed the
greatest number of gene mutations. Hundreds of normal
genes and their mutant alleles are known in these flies.
• The known gene mutations in Drosophila are those
causing white eyes, pink eyes, black body colour, yellow
body colour and vestigialwings.
• Similarly in man, many characters as hair colour, eyes
colour, skin pigmentation and several body deformities
are due to mutant gene.

10. Induced Mutations
• Induced mutations are alterations in the gene after it has
come in contact with mutagens and environmental causes.
• Induced mutations artificially through the use of
radiations, chemicals and other agent.
• It has been shown that the mutation rate can be raised
well above the spontaneous rate by various
experimental procedures.
• Temperature shocks were one of the first methods used to
raise the mutation rate.
• In Drosophila, short exposures to both low and high
temperature extremes outside the normal range result in
higher rate of mutation.

11. • X-rays and other ionizing radiations (alpha, beta and
gamma rays) induce mutations and cause chromosomal
breakage.At present, X-rays are considered to be the
most effective physical mutagens.
• Several chemicals are also strongly mutagenic. The
chemicals like formaldehyde and urethane when mixed
with food on which Drosophila larvae grow cause
mutations.
• caffeine, phenol and several cancer producing
compounds cause mutations.
• Mutations are also produced by the analogues of DNA
bases e.g., 5-Bromouracil, 5 Chlorouracil, which are
incorporated into newly formed DNAstrands.

12. PRACTICAL APPLICATIONS OF MUTATIONS
• Mutations are generally deleterious and
recessive for the organisms, therefore,
majority of them are of no practical value.
• A. Gustafsson has estimated that less than
one in 1000 mutants produced may be useful
in plant breeding.
• In India, several useful mutations of various
cereals and other crop plants have been
developed

13. • In bread wheat, many useful mutations have been
obtained and utilized in plant breeding, e.g.,
branched ears, lodging resistance, high protein and
lysine content, amber seed colour and awned
spikelets.
• In rice, one of the high yielding varieties Reimei was
developed through mutations isolated after gamma
irradiation. Certain developed mutants of rice are
found to contain increased contents of proteins and
lysine. In certain other mutant rice the duration of
crop was reduced by as many as 60 days.
• In barley, mutations called erectoides and
eceriferum have been induced. These mutants had
high yields including several useful characters.

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