Chromosome studies in 4 families of Falconiformes, Cathartidae, Falconidae, Sagittariidae and Accipitridae showed that the
karyological variety in this order is much wider than in any other avian order, which underlines the heterogeneous character
of the group. Of the 4 families only the Cathartidae show karyological similarities with other avian groups (Gruiformes, Ciconiiformes),
while the karyotypes of the Accipitridae are most uncommon among birds, because of the presence of only 8 microchromosomes.
This work was partially carried out at the Centre for Clinical Cytogenetics and the Institute of Genetics (both in Utrecht),
with the help of the Zoological Gardens of Wassenaar, Antwerp and Amsterdam.