# Fractional sketches ## or, some details of how sourmash and FracMinHash work! --- Consider overlaps between k-mers extracted from three genomes - two that share sequence, and one that does not. From these we can calculate k-mer based similarity measures (Jaccard similarity and containment).  --- ### FracMinHash sketching compresses k-mer collections while retaining set relationships  This is implemented in the software [sourmash](https://sourmash.readthedocs.io/en/latest/). --- ### These Jaccard (k-mer) measures can be translated to ANI  Credits: Dr. Tessa Pierce-Ward et al; [more info](https://github.com/sourmash-bio/sourmash/issues/1859). --- ### References: FracMinHash and sourmash - [Lightweight compositional analysis of metagenomes with FracMinHash and minimum metagenome covers](https://www.biorxiv.org/content/10.1101/2022.01.11.475838v2), Irber et al. 2022 ANI calculations - [Debiasing FracMinHash and deriving confidence intervals for mutation rates across a wide range of evolutionary distances, Hera et al.](https://www.biorxiv.org/content/10.1101/2022.01.11.475870v2), Hera et al., 2022