In the last over hundred years, genetics and molecular biology have gone far ahead and the progress has been very rapid. Today there is hope for cure of genetic disorders through gene therapy. This is because in 2003, most of the genes on human chromosomes have been mapped or located on the 23(n) chromosomes.

The genes responsible for inheritance of various structural features, that control various enzymes that catalyse the various biochemical reactions in the body, and genes responsible for genetic disorders have been located.

Genome means genes of a particular organism on its haploid set of chromosomes and study of genome is Genomics. Since genes are present in pairs (one inherited from mother and other from the father), all kinds of genes present in a particular type of organism are present in its haploid set (n).

Thus, human genome may be defined as all the genes present in the haploid set of chromosomes in humans. There are an estimated 20,000 to 25,000 genes and 3 billion base pairs in the total human DNA. Each human chromosome has apart from protein coding genes, regulating base sequences, non coding DNA, promoter sequences (TATA box) in between genes that code for proteins. There are genes that code for the production of ribosomal RNA and the many tRNAs.