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Life Science Research and Sustainable Development ISBN: 978-98-84663-33-9

The term “mutation” used in 1900 by Hugo de Vries, to describe phenotypic changes which were
heritable. However, the term ‘mutation’ is now used in a rather strict sense to cover only those
changes which alter the chemical structure of a gene at molecular level, are commonly called gene
mutations or point mutations. Structural changes in the chromosomes viz., deletions, duplication,
inversions and translocations also bring about phenotypic changes in plants and animals, are
called chromosomal mutations.
Mutations are classified depending upon the magnitude of phenotypic effect produced
by them into two groups (Gaul 1964).
(i) Macro mutations: In this type produce a large recognizable phenotype effect on
individual plants. These are oligogenic in nature and can be easily selected in the M2
generation
(ii) Micro mutations: These types of mutations produce a small phenotypic effect that can be
identified only on the basis of a population. These are polygenic in nature and selection
for such mutations can be delayed till M3 or later generations.
Types of Mutagens: In mutation breeding the agents available and responsible for
induction of mutations called mutagens. They are categorized into two classes: a) Physical
and b) Chemical mutagens.
Table .1: Physical mutagens
Mutagen Source Characteristics Hazard
X-rays X-ray machine Electromagnetic radiation; penetrates tissues from Dangerous,
a few millimeters to many centimeters penetrating
Gamma Radioisotopes Electromagnetic radiation produced by Dangerous,
rays and nuclear radioisotopes and nuclear reactors; very very
reaction penetrating into tissues; sources are Co (Cobalt- penetrating
60
60) and Cs (Caesium-137)
137
Neutrons Nuclear reactors There are different types (fast, slow, thermal); Very
or accelerators produced in nuclear reactors; uncharged particles; hazardous
penetrate tissues to many centimeters; source
is U
235
Beta Radioactive Produced in particle accelerators or from May be
particles isotopes or radioisotopes; are electrons; ionize; shallowly dangerous
accelerators penetrating; sources include P and C
14
32
Alpha Radioisotopes Derived from radioisotopes; a helium nucleus Very
particles capable of heavy ionization; very shallowly dangerous
penetrating
Protons Nuclear reactors Produced in nuclear reactors and accelerators; Very
or accelerators derived from hydrogen nucleus; penetrate tissues dangerous
up to several centimeters
Ion beam Particle Produced positively charged ions are accelerated at Dangerous
accelerators a high speed (around 20%–80% of the speed of
light) deposit high energy on a target

https://jesjalna.org/Zoology-Publications/index.html 2 Department of Zoology, J. E. S. College, Jalna