Synteny block definition:
First, all triplets of ECRs consecutively present in both species (two neighboring ECRs
were selected as consecutively located only if they were separated by <100kb in both
genomes) were extracted. These ECR triplets defined anchors of genome similarity and
then were used to construct long syntenic blocks by clustering ECR triplets together
using the 100kb threshold again. (Method originally described in Ovcharenko et. al, Genome Research, (2005).)