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A genome is an organism’s complete set of DNA, including all of its genes. Each genome contains all of the information needed to build and maintain that organism.

(https://www.nih.gov)

The genome consists of a full set of chromosomes. The major component of a chromosome is the deoxyribonucleic acid (DNA), which carries the genetic information. The genetic information is transcribed into the messenger ribonucleic acid (RNA). The triplets of messenger RNA are translated into different amino acids, the building blocks of protein. The DNA, the RNA, and protein are the source of life. The genomic information is generated by profiling alterations in DNA, RNA and protein levels. Genetics is the totality of heritable changes in the gene expression profiles caused by the modification of the genomic DNA as a result of the changes in sequence of its bases. Various human diseases, including cancer, are caused by changes in the genomic DNA sequence.

The Human Genome Project, which started in 1990 and was completed in 2003, determined the whole genome sequences of all the estimated 20,000 to 25,000 human genes and made them accessible to the public. This genome sequence information led to analysis of the genome-wide expression of cellular genes through genomic technology. The simultaneous monitoring of thousands of nucleic acid sequences through microarray technology became possible by quantifying the amount of specific transcripts. The global analysis of gene expression profiles provides a comprehensive view of toxicity and disease. Besides genomics, other new technologies of this kind, for proteins (proteomics) and for metabolites (metabolomics), yield useful information on toxicity and disease.

One major application of genomics is to identifying the genes that predict the effects of exposure to environmental chemicals. Such genes are sensitive and informative indicators of time- and dose-dependent adverse effects of chemical exposure. Therefore they are predictive biomarkers of toxicity and disease. The microarrays and DNA sequencing technologies provide powerful tools; they can identify biomarkers from gene expression profiles that show altered expression levels in thousands of genes at a time. Genome-wide analysis through these technologies leads to an understanding of toxicological and pathological changes at the RNA or DNA level.