MCBRATNEY-OWEN, B. M. ; OLSEN, B. R.; Harvard Medical School; Harvard Medical School: Mousehead Revisited – Microevolutionary Variation of the Cranial Base in Three Inbred Mouse Strains

In order to investigate the genetic architecture and molecular development of morphological variation, the magnitude of morphological divergence must first be investigated among the variation being studied. This study examines the morphological and genetic variation in mature midline cranial base elements of three inbred mouse strains: A/J, C57BL/6J, and DBA/2J. Qualitative variation in presphenoid, basisphenoid, and basioccipital bone morphology is evident between strains. A/J mice have distinctly narrow midline cranial base elements, such as the widths of the synchondroses and presphenoid body. In contrast, C57BL/6J mice have significantly wider cranial base elements than the other two strains. DBA/2J mice have fused and obliterated presphenoidal synchondroses and reduced rostro-caudal length of the fused presphenoid-basisphenoid bodies. The postoptic roots of A/J and C57BL/6J mice are perpendicular to the mid-sagittal axis while the postoptic roots are thin and latero-medially angled in DBA/2J mice. Euclidean Distance Matrix Analysis (EDMA) was also used to quantify and compare the form and shape patterns of two-dimensional linear distances measured between landmarks on cranial base elements in all three strains. Preliminary EDMA results show that the linear distances observed to be qualitatively different are indeed significantly different quantitatively. Finally, a multivariate analysis of variance will be used to test heritability and genetic variance between the strains. This study supports future research aimed at understanding the developmental basis and genetic architecture of microevolutionary variation of the cranial base in these inbred mouse strains.