Methodology:
- To identify all the genes that expressed as RNA referred as Expressed Sequence Tags (ETSs).
- Simply sequencing the whole set of genome that contained all the coding and non-coding sequence, and later assigning different regions in the sequence with functions called Sequence Annotation.
- The commonly used hosts for sequencing were bacteria and yeast and vectors were called as BAC (bacterial artificial chromosome) and YAC (yeast artificial chromosome).
Salient features of Human Genome:
- The human genome contains 3164.7 million nucleotide bases.
- The average gene consists of 3000 bases.
- The largest known human gene being dystrophin at 2.4 million bases.
- The total number of gene is estimated at 30.000.
- 99.9 percent nucleotide base sequences are same in all peoples.
- The function of 50% genes discovered is unknown.
- Less than 2 percent of the genome codes for proteins.
- Repeated sequences make up very large portion of human genome.
- Chromosome I has most genes (2968) and the Y has the fewest (231).
- It is identified about 1.4 million locations where single-base DNA differences (SNPs – single nucleotide polymorphism) occurs in humans.
DNA FINGER PRINTING:
- DNA finger printing is a very quick way to compare the DNA sequences of any two individual.
- DNA fingerprinting involves identifying differences in some specific regions in DNA called repetitive DNA, because in these sequences, a small stretch of DNA is repeated many times.
- During centrifugation the bulk DNA forms major peak and the other small peaks are called satellite DNA.
- Depending on base composition (A:T rich or G:C rich), length of segment, and number of repetitive units, the satellite DNA classified into many types, such as mini –satellite and micro – satellite.
- These sequences dose not code for any proteins.
- These sequences show high degree of polymorphism and form basis of DNA fingerprinting.
- Polymorphism in DNA sequence is the basis of genetic mapping of human genome as well as of DNA fingerprinting.
- Polymorphism (variation at genetic level) arises due to mutations.
- If an inheritable mutation is observed in a population at high frequency it is referred as DNA polymorphism.
The process:
- DNA fingerprinting was initially developed by Alec Jeffreys.
- He used satellite DNA as the basis of DNA fingerprinting that shows very high degree of polymorphism. It was called as Variable Number Tandem Repeats.(VNTR)
- Different steps of DNA fingerprinting are:-
- Isolation of DNA.
- Digestion of DNA by restriction endonucleases.
- Separation of DNA fragments by gel electrophoresis.
- Transferring (blotting) of separated DNA fragments to synthetic membranes, such as nitrocellulose or nylon.
- Double stranded DNA made single stranded.
- Hybridization using labeled VNTR probe.
- Detection of hybridized DNA fragments by autoradiography.
- The VNTR belongs to a class of satellite DNA referred to as mini-satellite.
- The size of VNTR varies from 0.1 to 20 kb.
- After hybridization with VNTR probe the autoradiogram gives many bands of different sizes. These bands give a characteristic pattern for an individual DNA. It differs from individual to individual.
- The DNA from a single cell is enough to perform DNA fingerprinting.
Applications:
- Test of paternity.
- Identify the criminals.
- Population diversity determination.
- Determination of genetic diversity.
CBSE Biology (Chapter Wise) Class XII ( By Mr. Hare Krushna Giri )
Email Id : harekrushnagiri@yahoo.com
