MUTATIONS -Causes,Types & Manifestations- EASY NOTES

 --Change in the base sequence of DNA due to faulty replication or faulty repair of DNA is called as Mutations.

--mutations affects somatic cells and so are carried to successive generations.

--due to horizontal transmission of mutations ,they  also results in many diseases.

--Mutations can be

    --Gross that involves large areas of a chromosome (or)

    --Subtle that involves only few nucleotides.

CAUSES OF MUTATIONS:

1.Errors in DNA repair Mechanisms

2.Spontaneous Change in DNA 

3.External/Environmental factors

    Physical Agents - Ultraviolet rays/Nuclear rays

    Chemical Agents - Deaminating/Alkylating agents

--Substance capable of causing mutations are called MUTAGENS.

TYPES OF MUTATIONS

1.POINT MUTATIONS/SUBSTITUTION:

--Replacement of one base by another base.

-- 2 types of point mutations - 

a) Transition - replacement of purine by purine and pyrimidine by pyrimidine respectively

b)Transversion - Replacement of purine by pyrimidine or vice versa

--Types of Point Mutation

2.FRAMESHIFT MUTATIONS

--due to insertion or deletion of one or more base pairs

-- results in altered reading of mRNA

--mRNA cannot recognize the deletion or insertion(because of the absence of any punctuations between the codons) and continues the translation process.

-- this ultimately results in the synthesis of a protein with completely different alteres amino acids and prematurely terminated protein.

MANIFESTATIONS OF MUTATIONS

1.Lethal Mutations -

--Mutations are present in such a way that it is incompatible with life.

-- e.g.- deletion of 4th gene causes of absence of alpha chain of HB leading to intrauterine death

2.Silent Mutations-

--Mutations are present in such a way that it does not have any effect on the metabolic activity.

3.Beneficial Mutations-

--Mutations are present in such a way that it is beneficial.

--e.g. production of tryptophan rich maize in agriculture.