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By J. F. Young and P. Palese. Proceedings of the National Academy of Sciences76(12),6547–6551(December1979). DOI doi.org/10.1073/pnas.76.12.6547

Abstract: oligonucleotide and peptide maps of A/Cal/10/78 support different parental origins for different influenza genome segments; inference distinguishes reassortment from sequential mutation.

J. F. Young studied genetic variation in Influenza A virus. In a 1979 paper with P. Palese, RNA oligonucleotide fingerprints and peptide mapping were used to compare circulating strains.^[ref]

The important comparison was between individual genetic segments, not just whole-strain labels. Different inferred parental origins within A/Cal/10/78 supported reassortment rather than explaining every difference by successive mutations. The evidence was comparative: the paper inferred ancestry from molecular patterns, rather than directly filming the historical exchange inside a cell.^[ref]

P. Palese investigated the genetic evolution of Influenza A virus. A 1979 study with J. F. Young compared RNA fingerprints and peptide mapping to infer the origins of different parts of a viral genome.^[ref]

The strain A/Cal/10/78 retained the H1N1 designation, yet the analysis suggested that some internal genetic segments came from an H3N2 parent. The result supported reassortment: a surface subtype need not describe the ancestry of every segment in a segmented genome. This distinction lets a scientist ask two different questions about the same virus: what surface antigens it carries, and where its complete genetic material came from.^[ref]

A segmented viral genome is a virus genome composed of two or more distinct nucleic-acid segments that together provide its genetic information. The phrase applies segmented genome organization specifically to viruses. In Influenza A virus, the eight Negative-sense RNA segments make inheritance a question of which complete segment set a progeny virus receives, as well as which mutations each segment carries.

When related viruses infect the same cell, progeny can receive segments with different parental origins through reassortment. This differs from exchanging sequence within a segment. J. F. Young and P. Palese compared oligonucleotide and peptide maps of influenza isolates and inferred that one strain combined surface-associated and other segments derived from different parental lineages. The evidence supported mixing of segment histories rather than explaining every difference by sequential mutation within one lineage.^[ref]

A three-segment toy model makes the combinatorics clear. If each segment type can come from either parent and exactly one copy of each type is selected independently, there are $2^3=8$ possible parental-origin combinations, including the two unmixed parental sets. This is an upper-counting illustration, not a prediction that all combinations occur equally or produce viable viruses: packaging, compatibility and selection can constrain the outcome.

Segmentation alone also does not specify the number of particles required to transmit the complete information. Genome organization and how components are packaged are related but distinct properties; they must be established for the virus being discussed.