This reduction in the number of ancestors is pedigree collapse, it collapses the binary tree into a directed acyclic graph with two different, directed paths starting from the ancestor who in the binary tree would occupy two places.
This reduction in the number of ancestors is pedigree collapse, it collapses the binary tree into a directed acyclic graph with two different, directed paths. These two different, directed paths are starting from the ancestor. This ancestor in the binary tree would occupy two places.