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Update 22-pract.md
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lkalmar committed Nov 7, 2024
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## Compositional mapping of shotgun metagenomics data

The previously used whole-genome alignment based mapping method works very well if we know what we are looking for, e.g., we try to detect a known pathogen or follow the dynamic changes in a synthetic community. When we try to describe the composition of more complex communities the potential reference database would be so big using whole genomes (Bacteria + Archea + Fungi + Virus), so we apply different reduction strategies. The two main approaches are:(i) Finding biologically meaningful genetic signatures (e.g., genes that are only present in certain taxonomic group) and search for those in the raw data; (ii) extract numerous random short fragments from genomes and try to find exact matchings for those in the raw data.
When we try to describe the composition of more complex communities the potential reference database would be so big using whole genomes (Bacteria + Archea + Fungi + Virus), so we apply different reduction strategies. The two main approaches are:(i) Finding biologically meaningful genetic signatures (e.g., genes that are only present in certain taxonomic group) and search for those in the raw data; (ii) extract numerous random short fragments from genomes and try to find exact matchings for those in the raw data.

### MASH, a random k-mer based profiling method

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```bash
mash screen -w mixed_community.msh NZ_CP034931.fa
mash screen mixed_community.msh NZ_CP038419_1.fasta
mash screen mixed_community.msh NZ_CP034931.fa

mash screen -w mixed_community.msh NZ_CP038419_1.fasta
mash screen mixed_community_hr.msh NZ_CP038419_1.fasta
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