A promising mouse model of DS with segmental trisomy is the Ts65Dn and has been studied since the early 1990s. The Ts65Dn mice are – because they carry an additional copy of chromosome 16, which is similar to chromosome 21 in humans. These mice showed that DS-relevant deficits in learning and memory as well as abnormalities in cellular and electrophysiological features (1). This skull of the Ts65Dn mice as well as their craniofacial skeleton display displays many direct parallel with developmental anomalies that are seen in DS (2). However this is not the ideal model because Ts65Dn mice carry only part of mouse chromosome 16 and not extra copies of all of its segments. They also carry a copy of mouse chromosome 17, which is not related to human chromosome 21 at all (1).

(1) Buckley, Frank. "Modelling Down syndrome." Down Syndrome Research and Practice 12.2 (2008): 98-102. (2) Olson, L. E., et al. "Down syndrome mouse models Ts65Dn, Ts1Cje, and Ms1Cje/Ts65Dn exhibit variable severity of cerebellar phenotypes." Developmental Dynamics 230.3 (2004): 581-589.