Segment Reassortment Combinations

Count independent segment-source combinations from parental strains; viability and packaging compatibility are not implied.

Description

Count theoretical parental-source assignments for segmented genomes and subtract the all-one-parent assignments.

Some viral genomes consist of separate segments. Reassortment exchanges whole segments when parental viruses contribute to a shared infection, creating a genome whose segments can have different parental origins. It differs from sequence recombination within a segment. Actual reassortment depends on biological compatibility and packaging, not only the number of possible source assignments.^[1]

A simple counting model treats each segment position as distinct and permits any supplied parent to provide each position independently. With n segment positions and p parents, p choices at each position give p^n total assignments. Of these, p use one parent for every position.

Segment Reassortment Combinations returns the total source assignments and the number that mix parental sources. It counts labels, without enumerating genome sequences, checking viability, or assigning probabilities.

When to count independent segment-source possibilities

Use this tool for a theoretical comparison or teaching example when each distinct segment position can be supplied by every listed parent. Treat the result as a combinatorial upper-level description rather than an expected biological yield.

Compare how segment and parental counts affect the number of assignments.
Separate all-one-parent assignments from mixed-parent assignments.
Check single-parent and single-segment boundary cases.

How to enter counts and calculate combinations

Enter Segment count as a positive integer number of distinct segment positions.
Enter Parental strain count as a positive integer number of parent labels available at every position.
Run the tool and read Segment source combinations and Nonparental combinations.

segmentSourceCombinations = parentalStrainCount^segmentCount; nonparentalCombinations = segmentSourceCombinations − parentalStrainCount

Nonparental here means not all positions come from a single parent; it does not mean a verified novel viable strain.

The implementation validates positive safe-integer inputs, screens the exponentiation size, calculates the power, and checks that the result remains an exact safe integer. Counts that exceed the exact-integer budget are rejected rather than returned approximately.

json

{
  "input": {
    "segmentCount": 3,
    "parentalStrainCount": 2
  },
  "output": {
    "segmentSourceCombinations": 8,
    "nonparentalCombinations": 6
  }
}

Case	Result
One parent, any accepted segment count	One total assignment; zero mixed-parent assignments.
One segment and p parents	p total assignments; zero mixed-parent assignments.
Zero or fractional count	Input error.

Limitations of independent source counting

Every parent is assumed to supply every segment, with independent choices. Missing segments and selective packaging are not modeled.
Assignments may share identical segment sequences. The number is not a count of distinct nucleotide genomes.
Compatibility, viability, fitness, coinfection frequency, and transmission are not established by the result.
The tool returns counts only, with no enumerated assignments or probability distribution.

Alternative or Complementary genome-structure checks

Use genome annotation to establish the segment positions and parent labels before counting. Genome notation describes molecule and replication class rather than segment compatibility. Deletion accounting addresses retained sequence length and should be kept separate from whole-segment source assignments.

References

RNA Virus Reassortment: An Evolutionary Mechanism for Host Jumps and Immune Evasion — PLOS Pathogens (2015)

Similar or alternative tools

Viral Genome Notation Parser
Parse canonical genome-type notation and Baltimore class without inferring segmentation.
Defective Genome Deletion Union
Count the union of supplied deletion intervals and retained genome bases.