I recently had a chance to learn a little about Bioinformatics, and ended up browsing the NIH's database of genomes here. Inside the genome data for any particular strain of a species, you'll find various files with file extensions like "ffa", "fna", "ffn" and "frn". These are FASTA files.
The file format of FASTA files is described pretty well on the Wikipedia link. I immediately wondered how difficult it would be to read the entire files and import them into a relational database. The difficult part of this work is, of course, parsing the FASTA files. In order to support that, I wrote an ANLTR4 grammar for FASTA files. The result is here. Once the parser is built, it's trivial to walk the AST and insert appropriate rows.
Update: the link to the source on the Antlr4 git: antlr/grammars-v4