Twin Studies: Research in Genes, Teeth and Faces

Abstract

This work is licenced under the Creative Commons Attribution-NonCommercialNoDerivatives 4.0 International (CC BY-NC-ND 4.0) License. To view a copy of this licence, visit http://creativecommons.org/licenses/by-nc-nd/4.0 or send a letter to Creative Commons, 444 Castro Street, Suite 900, Mountain View, California, 94041, USA. This licence allows for the copying, distribution, display and performance of this work for non-commercial purposes providing the work is clearly attributed to the copyright holders. Address all inquiries to the Director at the above address. FOREWORDThis book presents a unique account of a comprehensive research program on the genetics of teeth and faces, carried out over three decades at the School of Dentistry within the University of Adelaide by Professor Grant Townsend and colleagues. It is unique in several senses, firstly in that perhaps no other centre in the world has carried out such a long-term and wide-ranging program on so many facets of dentistry and craniofacial biology. But it is also unique in the sense that I know of no other academic endeavour that has so thoroughly documented its own history and intellectual progression, including the description not just of the main projects but also the smaller side-projects and all the people, including other researchers and students, who carried them out. Thus the book is not just a heartfelt 'thank you' to all the twins and their families who took part in these studies over the decades, but also a valuable scientific and photographic record of the research projects, their planning, execution and findings.I am privileged to have played some small part in this research program in introducing Grant and his team to structural equation modelling methods for analysis of twin data. The great attraction for me was (and still is) not only the inherent interest in the dentition, but that the measurements are so very reliable and the traits are so heritable. This is in contrast to my other domain of interest, human behaviour, where, for many traits, measurement is often quite unreliable and heritabilities are modest. Another appealing feature of the dentition is that the same basic structure of eight teeth is replicated four times -left and right sides, on both upper and lower jaws. This provides very rich opportunities for statistical modelling, and Grant and I spent many hours, days, weeks fitting what I think are rather elegant models to explain the genetics of tooth size.Another inherently appealing aspect of this research is that its research subjects are normal identical (monozygotic) and non-identical (dizygotic) twins growing up together in normal Australian households. In fact, the classical twin method -the comparison of the similarity of the two types of twins -is the most powerful design we have in humans to estimate the relative influence of genes and environment on any vi Twin Studies trait one cares to measure. Twins occur more or less at random throughout society, so carrying out a project of this size and duration represents q...

Three‐dimensional (3D) geometric morphometric analysis of human premolars to assess sexual dimorphism and biological ancestry in Australian populations

“…This study focused on two populations in Australia, i.e., one of European ancestry and the other of Indigenous Australians. Serial dental casts of permanent dentitions of 140 subjects were obtained from the Yuendumu (Brown, Townsend, Pinkerton & Rogers, ) and Australian Twin (Townsend, Pinkerton, Rogers, Bockmann & Hughes, ) collections housed in the Murray James Barrett Laboratory, Adelaide Dental School, The University of Adelaide. The Indigenous group included members of the Walpiri group living at Yuendumu, a Government settlement ∼290 km north‐west of Alice Springs, in the Northern Territory of Australia (Brown et al, ).…”

Frequency of Occurrence and Degree of Expression of the Parastyle in Several Modern Human Populations

“…Dental casts of twins of European ancestry and known zygosity, who are involved in an ongoing study of orofacial morphology and growth and oral health at the Adelaide Dental School, The University of Adelaide, were also included in this study (Hughes et al, 2014;Townsend et al, 2015). A total of 620 subjects from Cohort 1 were scored for parastyles with the casts of twin pairs sorted randomly and the operator blinded to zygosity.…”

Tooth morphometry using quasi-conformal theory

“…Our study focuses on 140 subjects from two populations in Australia, Western European origin obtained from the Australian Twin study [20], with one co-twin from each twin pair selected randomly. The dental casts of the permanent dentitions of the subjects were obtained from the Yuendumu and…”

“…The key to the unparalleled accuracy lies in taking into account the additional surface shape information using ideas from computational geometry and quasi-conformal theory. Illustration of our framework is done by applying the new algorithms to a dataset of tooth occlusal surfaces from Indigenous Australians [19] and Australians of European ancestry [20] (see Figure 1 for examples). More specifically, to capture and quantify the shape differences between the 3D surfaces in terms of the overall shape, the curvature and the positions of the anatomical landmarks, we extend our previous work on landmark-matching Teichmüller map [21] to achieve an accurate 1-1 mapping between them, and further develop a quasi-conformal shape analysis model based on our previous work [14] for performing a classification.…”

“…More specifically, to capture and quantify the shape differences between the 3D surfaces in terms of the overall shape, the curvature and the positions of the anatomical landmarks, we extend our previous work on landmark-matching Teichmüller map [21] to achieve an accurate 1-1 mapping between them, and further develop a quasi-conformal shape analysis model based on our previous work [14] for performing a classification. The classification results for the tooth Figure 1: Examples of the second upper premolar occlusal surfaces from two populations in Australia [19,20], with four landmarks of the buccal cusp, the lingual cusp, the mesial fossa pit and the distal fossa pit highlighted in red. Each row shows four specimens with the same ancestry and gender.…”