BY :VINITA SHISHODIA

WHAT IS MUTATION?Mutation is sudden discontinuous variation

in genotype and phenotype of an

organism due to change in chromosomes

and genes

In addition to recombination ,

mutation is another phenomenon that

leads to variation in DNA.

Depending on the cause mutation are of three types

Gene mutation

Chromosomal aberration

Genomatic mutation

Gene mutation

It is alteration of DNA due to change in nucleotide sequence .

Gene mutation may occur due to change in a single base pair of DNA ,known as point mutation

Change in more than one nucleotide pair is called gross mutation

A. Frame –shift mutation

1. Deletion : removal of one or more bases from nucleotide chain

2.Insertion : addition of one or more bases in a nucleotide chain

B. Substitution

1. Transition: when a purine base (A or G)is substituted by another purine base or pyrimidinebase (T or C) is substituted by another pyrimidine base

2. Transversion :substitution of a purine base with a pyrimidine base or vice versa

Chromosomal aberrations

Chromosomes are made up of proteins ,DNA and RNA .Each chromatid possesses one DNA helix that runs continously from one end to the other . In chromatids , DNA is present in a highly supercoiled form . Therefore loss or gain of a segment of DNA , results in alteration in chromosomes .

We know that genes are located on chromosomes ,so that alteration in chromosomes results in abnormalities or aberration

Chromosomal aberrations are divided into two parts DELETION DUPLICATION

Occurs when a part of the chromosomes is lost

It can be of two types one is terminal

two is interstitial deletion

Occurs due to addition of a part of chromosomes so that a gene or set of genes is represented twice

Genomatic mutation

It is change in chromosome number that brings about visible effects on the phenotype

It is of two types : ANEUPLOIDY and EUPLOIDY

Aneuploidy

Aneuploidy is change in number of chromosomes which can be either due to addition or deletion of one or more chromosomes

The nuclei of aneuploidy is not true multiple of the basic number (n)

Loss of one chromosomes produces a monosomic (2n-1) and the gain of one chromosomes produces a trisomic (2n+1)

Euploidy

Euploidy is the state of a cell or organism having andmultiple of the monoploid number ,possibly excluding the sex –determingchromosomes

For example , a human cell has 46

chromosomes ,which is an integer multiple of the monoploid number 23