(i) Taxonomy browser: This search tool provides taxonomic information on various species. The TAXONOMY database of NCBI has information (including scientific and common names) about all organisms for which some sequence information is available (over 79,000 species). The server provides genetic information and the taxonomic relationship of the species in question. TAXONOMY has links with other servers of NCBI e.g., structure and PubMed. 

(ii) BLAST (Basic Local Alignment Search Tool) : BLAST is a family of user-friendly sequence similarity search tools on the web. The BLAST server is supported through NCBI (National Center for Biotechnology Information) U.S.A. This tool is designed to identify potential homologous for a given sequence. It can analyse both DNA and protein sequences. A local alignment finds the optimal alignment between subregions or local regions of specified sequences. 

(iii) ENTREZ: Integrated information database retrieval system of NCBI. Using Entrez system you can access literature, sequences (both proteins and nucleotides) and structures (3D). 

(iv) EMBL (European molecular Biology Laboratory- Nucleic Acid (DNA sequence) databases.