MBI - DNA Fingerprinting Flashcards
what is satellite dna/ repetitive dna
Repetitive DNA refers to DNA that contains a short sequence of bases that is repeated many number of times.
These sequences normally
do not code for any proteins, but they form a large portion of human
genome. These sequence show high degree of polymorphism and form
the basis of DNA fingerprinting.
how is human genome different from each other?
99.9 per cent of base sequence among
humans is the same but very small amount (0.1%) that differs from person to person.
- Human genome = 3.3 × 109 bp
- 0.1% different = 3.3 × 106 bp
It is these differences in sequence of DNA which make every individual unique in their phenotypic appearance.
how is repetitive dna demarcated from the bulk dna
These repetitive
DNA are separated from bulk genomic DNA as different peaks during
density gradient centrifugation. The bulk DNA forms a major peak and
the other small peaks are referred to as satellite DNA.
major peak- coding part, non repetitive dna, some repetitive dna
minor peak- repetitive/ satellite dna
types of satellite dna
Depending on
base composition (A : T rich or G:C rich), length of segment, and number
of repetitive units, the satellite DNA is classified into many categories,
such as micro-satellites, mini-satellites etc.
- Micro-satellites- This satellites has 1 to 6 bp repetition, also called SSR
(Simple Sequence Repeat)/ STR (Short Tandem Repeats) - Mini-satellites-
1. This satellites has 11 to 60 bp repetition.
2. Also called VNTR (Variable Number of Tandem Repeats).
3. Size of VNTR varies in size from 0.1 to 20 kb.
4. At the end of VNTR palindromic sequence is present.
5. The repetition number of VNTR is vary in homologous chromosomes of an
individual. So, DNA of all human beings are slightly different except
monozygotic twins.
what is meant by DNA polymorphism
Definition: DNA polymorphism refers to variations or differences at the genetic level (in DNA sequences) within a population. These variations are caused by mutations.
Arises Due to Mutations: Mutations in DNA, occurring in either somatic or germ cells, lead to polymorphisms. If these mutations happen in germ cells and do not impair reproduction, they can be passed down through generations.
Allelic Variation: When mutations create different versions (alleles) of a gene, these variants can exist at the same location (locus) on a chromosome. If a variation occurs in the population at a frequency greater than 1% (0.01), it is referred to as DNA polymorphism.
Inherited Mutation: For a mutation to be classified as polymorphism, it must be inheritable and observed in a population at a high frequency.
Non-Coding DNA: Polymorphisms are more likely to occur in non-coding regions of DNA. Since mutations in non-coding regions usually don’t affect an individual’s reproductive ability, these mutations accumulate over generations.
Types of Polymorphisms: DNA polymorphisms can range in size from small changes like a single nucleotide substitution to larger scale changes, such as duplications or deletions of larger DNA segments.
who developed dna fingerprinting technique
The technique of DNA Fingerprinting was initially developed by Alec
Jeffreys.
principle of dna fingerprinting
He used a satellite DNA as probe that shows very high degree
of polymorphism. It was called as Variable Number of Tandem Repeats
(VNTR). The technique, as used earlier, involved Southern blot
hybridisation using radiolabelled VNTR as a probe.
steps of dna fingerprinting
- Isolation of DNA
- Digestion of DNA by restriction endonucleases
- Separation of DNA fragments by electrophoresis
- Transferring (blotting) of separated DNA fragments to synthetic membranes,
such as nitrocellulose or nylon - Hybridization using labelled VNTR probe
- Detection of hybridized DNA fragments by autoradiography
how are the results analysed
Consequently,
after hybridisation with VNTR probe, the autoradiogram gives many bands
of differing sizes. These bands give a characteristic pattern for an individual
DNA (Figure 5.16). It differs from individual to individual in a population
except in the case of monozygotic (identical) twins.
The VNTR probe is radioactive and completementary the vntrs present in the dna of theperson. SO on utordiography, we can see which matches.
The sensitivity of the
technique has been increased by use of polymerase chain reaction (PCR–
you will study about it in Chapter 9). Consequently, DNA from a single
cell is enough to perform DNA fingerprinting analysis.
what i mini satellite ( TEXTBOOK)
The VNTR belongs to a class of satellite DNA referred to as mini-satellite.
A small DNA sequence is arranged tandemly in many copy numbers. The
copy number varies from chromosome to chromosome in an individual.
The numbers of repeat show very high degree of polymorphism. As a
result the size of VNTR varies in size from 0.1 to 20 kb.
uses of dna fingerpritnting
Since DNA from every tissue (such as
blood(wbc), hair-follicle, skin, bone, saliva, sperm etc.), from an individual
show the same degree of polymorphism, they become very useful
identification tool in forensic applications.
Further, as the polymorphisms
are inheritable from parents to children, DNA fingerprinting is the basis
of paternity testing, in case of disputes.
it has much wider application, such as in determining population and genetic diversities.
