`star` Convenience due to DNA fingerprinting
`star` Principle
`star` Practical Applications
`star` Polymorphism


● According to Human Genome Project, `color{Violet}"99.9 per cent"` of `color{Violet}"base sequence"` among humans is the `color{Violet}"same"`.

● Assuming human genome has 3 × `10^9` bp, 3 × `10^6` base sequences would be `color{Violet}"different"` in different individuals.

● It is these differences in sequence of DNA which make every `color{Violet}"individual unique"` in their `color{Violet}"phenotypic appearance"`.

● If one aims to find out `color{Violet}"genetic differences"` between two individuals or among individuals of a population, sequencing the DNA every time would be a `color{Violet}"daunting and expensive task"`.

● Imagine trying to compare `color{Violet}"two sets"` of 3 × `10^6` base pairs.

● DNA fingerprinting is a very `color{Violet}"quick way to compare the DNA"` sequences of any two individuals.


● DNA fingerprinting involves `color{Violet}"identifying differences"` in some specific regions in DNA sequence called as `color{Violet}"repetitive DNA"`, because in these sequences, a `color{Violet}"small stretch of DNA"` is repeated many times.

● These `color{Violet}"repetitive DNA"` are separated from `color{Violet}"bulk genomic DNA"` as different peaks during `color{Violet}"density gradient centrifugation"`.

● The `color{Violet}"bulk DNA"` forms a `color{Violet}"major peak"` and the other `color{Violet}"small peaks"` are referred to as `color{Violet}"satellite DNA"`.

● The satellite DNA is classified into many categories, such as `color{Violet}"micro-satellites"`, `color{Violet}"mini-satellites"` etc, depending on:

`star` `color{Violet}"Base composition"` (A : T rich or G:C rich)

`star` `color{Violet}"length of segments"`

`star` `color{Violet}"Number of repetitive units"`.

● These sequences normally `color{Violet}"do not code"` for any proteins, but they form a `color{Violet}"large portion"` of human genome.


● These sequence show `color{Violet}"high degree of polymorphism"` and form the `color{Violet}"basis of DNA fingerprinting"`.

● Since DNA from `color{Violet}"every tissue"` (such as blood, hair-follicle, skin, bone, saliva, sperm etc.), from an individual show the `color{Violet}"same degree of polymorphism"`, they become very useful identification tool in `color{Violet}"forensic applications"`.

● Further, as the polymorphisms are `color{Violet}"inheritable"` from `color{Violet}"parents to children"`, DNA fingerprinting is the basis of `color{Violet}"paternity testing"`, in case of disputes.

● As polymorphism in DNA sequence is the `color{Violet}"basis of genetic mapping"` of human genome as well as of `color{Violet}"DNA fingerprinting"`, it is essential that we understand what DNA polymorphism means in simple terms.


● `color{Violet}"Polymorphism"` (variation at genetic level) arises due to `color{Violet}"mutations"`.

● `color{Violet}"New mutations"` may arise in an individual either in `color{Violet}"somatic cells"` or in the `color{Violet}"germ cells"` (cells that generate gametes in sexually reproducing organisms).

● If a germ cell mutation does not seriously `color{Violet}"impair individual’s ability"` to have `color{Violet}"offspring"` who can transmit the mutation, it can `color{Violet}"spread"` to the `color{Violet}"other members"` of population (through `color{Violet}"sexual reproduction"`).

● `color{Violet}"Allelic sequence variation"` has traditionally been described as a `color{Violet}"DNA polymorphism"` if more than one variant (`color{Violet}"allele"`) at a locus occurs in `color{Violet}"human population"` with a frequency `color{Violet}"greater than 0.01"`.

● In simple terms, if an `color{Violet}"inheritable mutation"` is observed in a population at `color{Violet}"high frequency"`, it is referred to as `color{brown}"DNA polymorphism"`.

● Probability of such variation to be observed in `color{Violet}"non coding DNA sequence"` would be `color{Violet}"higher"` as mutations in these sequences may not have any immediate effect/impact in an `color{Violet}"individual’s reproductive ability"`.

● These mutations keep on `color{Violet}"accumulating generation after generation"`, and form one of the basis of `color{Violet}"variability/polymorphism"`.

● There is a `color{Violet}"variety"` of different types of polymorphisms ranging from `color{Violet}"single nucleotide change"` to very `color{Violet}"large scale changes"`.

● For `color{Violet}"evolution and speciation"`, such polymorphisms play very `color{Violet}"important"` role.