What is a FASTA format file ?



I am a bit confused about what is the meaning of having a FASTA format file. If I download the sequence of a genome from NCBI by choosing the options "Send to">"Coding Sequences">"Format:FASTA Nucleotide", I obtain a file in which I have the sequences of the genes and each one starts with a ">" and the description.

It should be a FASTA format file in this way, right ? But, actually, this file that I download is a txt file ... So how should I consider it ? The organization in the file is like a FASTA format file but the file is a txt file. What can I do to have a real FASTA format file ?

Sorry if my question could be trivial but I am pretty new in this field. Thank you in advance.

P.s. I am on Windows 10 and not on Linux.







updated 2 hours ago by


written 4 hours ago by



That is likely an oddity of your OS/browser. It added the ".txt" extension since it recognized the data as plain text which FASTA format data is. Using ChromeOS a FASTA file gets downloaded as sequence.fasta, no .txt added.

Here is a tip. If you get a save file as dialog then you can add double quotes around the file name (e.g. "sequence.fasta") and the file should be saved with that name without .txt extension.

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