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DNA

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CHROMOSOME

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MUTATION

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TYPES OF MUTATION

Spontaneous and Induced Mutations:

Mutations occurring naturally without any knowncause are called spontaneous mutations.

Mutation caused by mutagens- induced mutation

Somatic and Germinal Mutations:

A mutation occurring in a body cell other than the

reproductive cells is called a somatic mutations.Germinal mutations occur in reproductive tissues

and are passed onto the next generation throughthe gametes.

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Forward and Reverse Mutations:

When a normal gene mutates into its allelethat produces a mutant phenotype, it is calledforward mutation.

When a mutation in the mutant allele restores

the normal phenotype, it is called reversemutation or back mutation, or reversion.

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MUTATIONS:

POINT MUTATIONS:

changes in the nitrogen base pair sequence ofDNA or a gene: base substitution, deletion,

addition (insertion) and nucleotides repeatexpansion.

1. Base Substitution:

Nitrogen base pair of DNA is substituted byanother base pair, it is called base substitution.2 types:

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Transition

When a purine is replaced by other purine or apyrimidine is replaced by the other pyrimidineas follows:

A G or C T

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Transversion

When a purine is replaced by a pyrimidine and viceversa.

A C

T G

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ypes o u a on ue o aseSubstitution

Missence mutation

Silent mutation

Non-sense mutation

Missense mutation:

The new codon causes an incorrect AMINOACID to be inserted into the protein. This effect

on the function of the protein depend on whatis inserted in place of normal amino acid.

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Non-sense mutation:

The new codon causes the protein toprematurely TERMINATE, producing a product

that is shortened and often does not function.

Silent mutation:

Silent mutation does not causes any change in

amino acid. (Silent mutation codes for sameamino acid)

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2. Base Addition and Base Deletion

Deletion:

Mutations that result in MISSING DNA are called

DELETIONS.Deletions can also cause frame-shift mutation

For example

ORIGINAL DELETIONThe fat cat ate the wee rat The fat ate thewee

rat

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Insertions:

Mutations that result in the addition of extra DNA arecalled insertions.

Insertions can also cause frame shift mutations,and general result in a nonfunctional protein.

For example:

ORIGINAL INSERTION:The fat cat ate the wee rat The fat cat xlv ate the

wee

rat

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3. Repeat Expansion:

Nucleotide repeats are short DNA sequencesthat are repeated a number of times in a row.