Lesson 1: Mutation

1. Classification of mutation

Mutations are changes to the nucleotide sequence of the genetic material of an organism.  Mutation may cause changes in the number, structure of chromosomes or structure of gene. It may also cause changes in phenotype or physiological processes in the organism. There are 2 types of mutation:

Spontaneous mutation 

Mutation which appear suddenly. They may originate as errors during DNA replication or from chemical        changes in the DNA’s nitrogenous base.

Induced mutation 

Mutation which caused by mutagen such as radioactive material or methylating agents. these agents can mutate both replicating and non-replicating DNA. In contrast, a base analog can only mutate the DNA when the analog is incorporated in replicating the DNA. Each of these classes of chemical mutagens has certain effects that then lead to transitions, transversions, or deletions. 

Effect of Mutation

• Synthesis of a non-functional/faulty protein

• Lowers production of a particular protein

• Prevents the synthesis of a protein

• Adds more nucleotides bases to the gene, giving the protein product  new function which may be harmful to the cells

In multicellular organisms, mutations can be subdivided into :-

Germ line mutations, 

It is a mutation which can be passed on to descendants

Somatic Mutation

A mutation which are not transmitted to descendants in animals. The individual has different genotypes in the somatic cells but have developed from the same zygote. The individual is known as genetic mosaic. Somatic mutation only occur in somatic cells or tissues and are not transmitted. These mutation can only reproduce by mitosis. Plants sometimes can transmit somatic mutations to their descendants asexually or sexually (in case when flower buds develop in somatically mutated part of plant). 

Types Of Mutagens 

. 1. Ionising radiation(e.g: X-rays, alpha&beta particles, cosmic rays)   

• It can cause molecules to lose electron and production of highly reactive free radicals. It can cause aberrations/ difference in chromosomes and genes including breaks in DNA strands, destructive of  nucleotide bases.

.2. Non-ionising radiation (e.g: UV rays)

•  It causes molecular vibration or ejection of electron to higher energy level and cause breaking and formation of new chemical bonds which causes alteration of DNA strands. For Example: U.V light causes breakage of A & T bases and cause cross covalent bonds occurs between 2 adjacent thymine to form thymine dimer which cause distortion of DNA helix, prevent normal base pairing and impede replication or transcription