I. Chromosome, DNA:
Chromosome is a chain of DNA wrapped in a proteinous pellicle. DNA consists of a linear series of nucleosomes. Each nucleosome consists of a group of protein molecules (8 molecules of histone) wrapped around twice by DNA. The dense mass of loops and coils inside the nucleus constitute the chromatin. It occurs in two forms, namely, heterochromatin and euchromatin. The entire DNA does not code for formation of proteins. Some parts of DNA codes for specific proteins. Some part of DNA is involved in regulating the expression of the genes that codes for synthesis of specific proteins. The remaining non functional DNA is called Junk DNA. A complete set of DNA molecules in an organism is known as genome. The genetic information of an organism lies in the sequence of nitrogen bases in DNA molecule.
 

II. Human Genome Project (HGP):
HGP was a mega project of 13 years which was coordinated by U.S. Dept. of Energy & National Institute of Health. It was supported by UK, Japan, France, Germany, China etc. It was started in 1990 and completed in 2003. HGP was closely associated with the development of Bioinformatics.

III. Goals of HGP
* Identify all the genes in human DNA (20,000 - 25,000 genes).
* Determine the sequence of 3 billion base pairs that make up human genome.
* Improve tools for data analysis.
* Address the ELSI (Ethical, Legal and Social Issues) that may arise from the project.
 

IV. Salient features of HGP
* Human genome contains 3164.7 million nucleotide bases.
* On the average, a gene contains 3000 bases, but sizes vary greatly (The largest human gene codes for dystrophin).
* Total no. of genes is estimated as 30,000 (99.9% of nucleotide base pairs are same in all people).
* Among the genes discovered, the functions of about 50% of them are unknown.
* Less than 2% of the genome codes for proteins.
* Repeated sequences make up very large portion of the human genome.
* Chromosome-1 has the highest number of genes (= 2,968) and Y - chromosome has the least number of chromosomes (231).

* Scientists have identified about 1.4 million locations where single base DNA sequences occur in human beings. It promises to revolutionise the process of finding chromosomal locations for disease associated sequences and tracing human history.
 

V. Advantages of HGP
Health care: Identification and mapping of the genes responsible for genetic diseases help in diagnosis, treatment and prevention of these diseases.
* Detailed knowledge of the HG and other species will give a clear picture of gene expression, cellular growth and differentiation.
* Earlier detection of genetic predispositions to disease, rational drug design, Gene therapy is going to be easy with more knowledge on human genome.
Molecular medicine: A new era in it is characterised by looking into the most fundamental causes of disease than treating the symptoms will be an important advantage.
 

VI. DNA finger printing
DNA finger printing is a method for identifying individual by the particular structure of their DNA. Out of 3 billion nucleotide pairs in human beings, 99.9% are similar. The differences in sequence of DNA which make every individual unique in his phenotype. Restriction Fragment Length Polymorphisms (RFLPs) are characteristic to DNA of every person. They are called Variable Number Tandem Repeats (VNTRs) and are useful as genetic markers.

DNA Finger Printing Protocol

* A sample of DNA is to be obtained from blood, saliva, hair roots, semen etc. If required, many copies of this DNA are to produced by cloning/DNA amplification.
* This DNA is treated with restriction endonucleases to cut the DNA into smaller fragments at specific sites.
* These DNA fragments are applied at one end of agarose gel plate. When electric current is applied to the gel, the DNA fragments travel across the gel.
[The technique of separation of DNA fragments into individuals bands is called gel electrophoresis.]
* Then the DNA on the gel is denatured by using alkaline chemicals or by heating (Splitting of double helix of DNA into single strands is called denaturation).
* A thin nylon membrane is placed over the DNA strands and covered by paper towels. They draw moisture from DNA strands transferred on the nylon membrane (This process is called Southern Blotting after the name of E.M. Southern).
* A radioactive probe (DNA labelled with a radio active substance) is added to the DNA bands. This probe is a single strand DNA that is complementary to the gene of interest. The probe is attached to the base pairing to those restriction fragments that are complementary to its sequence (The probes are prepared by using fluorescent substances or radioactive isotopes).

* After the probe hybridises and the excess probe washed off, a photographic film is placed on the membrane containing DNA hybrids.
* Exposure on the film the radioactive label exposes the film to form an image corresponding to specific DNA bands. The thick and thin dark bands form a pattern of bars which constitute a genetic finger print.
 

VII. Applications of DNA finger printing
* Medico legal applications         * Forensic analysis
* Pedigree analysis                      * Taxonomical studies
* Anthropological studies            * Conservation of wild life