Polymerase
The copy machine. Error rate sets how fast a cloud of mutants appears.
Biology here is population genetics with a very short generation time. Billions of copies make rare events visible.
Drift accumulates in surface genes under antibody pressure. Shift is a different mechanism and a different historical timescale.
Parts
Genome segments or one piece
Influenza is segmented; many other RNA viruses are not. Architecture changes what 'mixing' can mean.
Surface antigens
HA/NA or spike are what antibodies often see first; their change drives much seasonal language.
Within-host cloud
A single infection is already a mixture. Sequencing a swab reports a consensus plus minority variants.
Bottleneck
Few particles start the next host, so much diversity is thrown away at each transmission.
Immune landscape
Prior infection and vaccination reshape which mutants can grow in a population this winter.
Life cycle
1Replication burst
Cells make huge numbers of genomes; errors appear as a matter of statistics.
2Mixed swarm
Related mutants coexist; most never become a headline name.
3Filter of hosts
Transmission and immunity amplify some genomes and extinguish others.
4Named lineage
If a cluster spreads widely, laboratories and WHO may file it for vaccines and risk talk.
Engineering steps are out of scope. The useful picture is selection on existing diversity in nature and clinics.
Keep exploring
More in Change & defence
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A shared drug budget under selection in hospitals, farms and wastewater — stewardship, not a lab manual.
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Antibodies, memory cells and community arithmetic — conceptual, not a prescription and not an anti-vaccine tract.
Familiarity 94Biofilms
Surface cities of microbes — plaque and catheters explain persistence, without a grow-your-own kit.
Familiarity 38Hygiene and balance
Clean water saves lives; missing old microbial partners is a separate, still-debated immune story.
Familiarity 70Horizontal gene transfer
Sideways DNA traffic — conjugation, transduction, transformation as names and history, not protocols.
Familiarity 45