Answer:
Sister taxa always share a most recent common ancestor that is not shared with any other taxon on the phylogeny.
Step-by-step explanation:
Phylogenetic trees are diagrams representing these relationships of ancestry and descent, consisting of lines that branch according to the past existence of an event that transformed one species into two new species. The junction of this fork is called a knot, where it represents this moment of diversification and the common ancestor of the species that are located at the tip of each fork.
In this type of diagram it is possible to see that sister taxa always share a more recent common ancestor that is not shared with any other phylogeny taxon. This is because sister taxa are the closest monophyletic group to another monophyletic group. Both sister taxa share a unique common ancestor.