Segmented genome

A segmented genome is genetic information distributed across separate nucleic-acid molecules rather than a single continuous genomic molecule. In its common virological use, the segments are the distinct components of a segmented viral genome. Segmentation concerns physical organization, rather than the number of genes: one segment can contain information for more than one product.

Influenza A virus provides a familiar example with eight Negative-sense RNA segments. Sequence maps can therefore ask two different questions: what mutations occurred within each segment, and whether different segments have different parental histories. Reassortment changes the combination of whole segments, while a mutation changes sequence within a segment.^[ref]

For an invented arithmetic example, three segments of lengths 2,000, 1,500 and 1,000 nucleotides contain 4,500 nucleotides of genomic sequence. Concatenating them into one computer file does not turn them into one physical molecule. Conversely, breaking one molecule during sample preparation does not establish that the original genome was biologically segmented.

Segment count, gene count and molecule copy count should therefore be reported separately. A particle might contain multiple copies of a particular segment without gaining a new segment type. Physical or sequence evidence is needed to distinguish complete genomic components from degradation products and incomplete samples.