Weight by ortholog group taxa span
The "weight by ortholog group taxa span" choice gives users a control over their preference for ortholog groups containing different levels of species diversity. Specifically, in BlastO the ortholog group scores are further weighted by the taxonomic span of the group, measured by the number of species in a particular ortholog group (Tg) divided by the total number of species included in the ortholog database (T). Different weights can be chosen on the main Blast form. The weighted score is:
, when weight is a real number.
When weight is ∞, the ortholog groups are ranked by the included number of species in a descending manner; when the weight is - ∞, the ortholog groups are ranked by the included number of species in an ascending manner.
In general, higher (positive) weight favors ortholog groups that contain genes from more species; these ortholog groups are therefore likely to be more ancient and conserved. Lower (negative) weight favors ortholog groups with genes from fewer species; these are therefore likely to be more recent or possibly confined to a subgroup of the species.