[jfmercer]

Of particular interest to me was how pedigree collapse transforms our family trees from exponentially growing binary trees into directed acyclic graphs.

We are accustomed to thinking that, because we have four unique grandparents, we must have eight unique great-grandparents. But this is not always so. For example, if our grandparents are two brothers who married two sisters, then we have four great-grandparents, not eight.