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Molbiotools is a collection of free online apps:

DNA Sequence Tools
Text and Data Tools
Lab Calculators
Math Calculators

Random Sequence Generator

A free online tool made to generate random DNA, RNA and protein sequences. It also offers a set of additional operations that can be apllied both to the generated sequences and to sequences provided by the user.

GC content (%):

Select All
a ⇨ A
A ⇨ a
Reverse Complement
Format Sequence
Clean Sequence

Additional Formatting of the Sequence

Insert a line-break after everycharacters to justify the sequence into a text block

Sequence Length Warning

Attempts to generate very long sequences (e.g. a million characters or longer, depending on the computer performance) may make the web browser jerky or even frozen. Significant time (a second per each 100,000 characters or so, depending on the computer) will be required to complete such tasks.


Amino Acid Frequency

Amino acid composition of natural proteins shows a strong overrepresentation of some amino acids (e.g. leucine and alanine) and underrepresentation of others (e.g. cysteine and tryptophan). To generate a sequence that mimics composition of natural proteins, check the "UniProt average" option. The "Equal" option will generate a sequence with approximately equal represantation of all amino acids.


Sequence Formatting

By default, the generated sequence contains no line breaks (it is one line text even though it is displayed as a justified block). To truly justify the sequence into a text block, regularly spaced line breaks must be inserted. This is done by the "Format Sequence" operation (if set to do so). The "Clean Sequence" operation will do just the opposite, i.e. remove all numbers, spaces, and line breaks to get a one-line sequence.
The "Format Sequence" and "Clean Sequence" functions will also process any external sequence pasted in the Sequence Output field.