Principles of Plant Breeding (2+1)

Mutagens: Physical mutagens

Mutagens: Agents which induce mutation are known as mutagens.
There are two types of mutagen.

• Physical Mutagens
• Chemical Mutagens
 
Mutagen	Characteristics
X- rays	Electromagnetic radiation; penetrate tissues from a few millimeters to many centimeters first discovered by Roentgen 1895 wavelength varies from 10-11 to 10-7. Highly penetrating they break chromosomes and produce all types of mutation in the nucleotides like addition, deletion, inversion, transition and transversion.
Gamma rays	Electromagnetic radiation produced by radioisotopes and nuclear reactors; very penetrating into tissues; sources are Co60 and Ce137 largely used in crop plants
Neutrons	A variety exists (fast, slow, thermal); produced in nuclear reactors; uncharged particles; penetrate tissues to many centimeters; source is U235
Beta particles	Produced in particle accelerators or from radioisotopes; are electrons; ionize; shallowly penetrating; sources include P32 and C14
Alpha particles	Derived from radioisotopes; a helium nucleus capable of heavy ionization; very shallow penetrating
Protons	Produced in nuclear reactors and accelerators; derived from hydrogen nucleus penetrate tissues up to several centimeters
Non ionizing radiations	Non-ionizing radiation produced from mercury vapor lamps or tubes. They penetrate one or two cell layers eg. Pollen.