Scientific & Technical Reference Library

Reference pages related to sequence file formats, basic sequence handling and common metrics used in bioinformatics sanity checks.

Sequence alphabets and IUPAC codes (DNA, RNA, protein)

Which letters are expected for DNA, RNA, and protein sequences.

DNA IUPAC • RNA letters • Amino acids

FASTA and FASTQ formats (structure, examples)

FASTA/FASTQ record structure, minimal examples, paired-end layouts, and common pitfalls.

FASTA records • FASTQ 4-line records • Quality encodings

Reverse complement of DNA and RNA sequences

Definitions and examples for complement, reverse, and reverse complement operations on DNA and RNA sequences.

Complement vs reverse complement • Practical examples

Sequence statistics explained: N50, N90, GC%

Descriptive statistics commonly computed from FASTA and FASTQ files, including sequence/read counts, length metrics, N50/N90, and GC%.

Sequence and read counts • Length metrics • N50/L50 and N90/L90

FASTQ quality scores (Phred, ASCII encoding, FASTQ variants)

How FASTQ quality strings work: Phred score meaning, ASCII encoding (Phred+33), and why older FASTQ variants can break pipelines.

Phred score meaning • ASCII (Phred+33) encoding • Legacy FASTQ variants

Looking for a quick structural check? Start with FASTA/FASTQ Validator or Sequence Stats.