Genetic influences on dentognathic morphology in the Jirel population of Nepal

Abstract

Patterns of genetic variation and covariation impact the evolution of the craniofacial complex and contribute to clinically significant malocclusions in modern human populations. Previous quantitative genetic studies have estimated the heritabilities and genetic correlations of skeletal and dental traits in humans and nonhuman primates, but none have estimated these quantitative genetic parameters across the dentognathic complex. A large and powerful pedigree from the Jirel population of Nepal was leveraged to estimate heritabilities and genetic correlations in 62 maxillary and mandibular arch dimensions, incisor and canine lengths, and post-canine tooth crown areas (N ≥ 739).Quantitative genetic parameter estimation was performed using maximum likelihood-based variance decomposition. Residual heritability estimates were significant for all traits, ranging from 0.269 to 0.898. Genetic correlations were positive for all trait pairs. Principal components analyses of the phenotypic and genetic correlation matrices indicate an overall size effect across all measurements on the first principal component. Additional principal components demonstrate positive relationships between post-canine tooth crown areas and arch lengths and negative relationships between post-canine tooth crown areas and arch widths, and between arch lengths and arch widths. Based on these findings, morphological variation in the human dentognathic complex may be constrained by genetic relationships between dental dimensions and arch lengths, with weaker genetic correlations between these traits and arch widths allowing for variation in arch shape. The patterns identified are expected to have impacted the evolution of the dentognathic complex and its genetic architecture as well as the prevalence of dental crowding in modern human populations.

Integrating genealogy and dental variation: contributions to biological anthropology

“…Consistent across studies is the strong pleiotropic relationship among antimeres, with genetic correlations often exceeding 0.9, alongside reasonably high derived phenotypic correlations. Indeed, this result is common to quantitative genetic studies of size and morphology in genealogical samples of mice (Hlusko et al, 2011), baboons (Hlusko et al, 2004; Hlusko & Mahaney, 2003; Koh et al, 2010), and several contemporary human populations (Hardin et al, 2022; Paul, Stojanowski, Hughes et al, 2021; Paul et al, 2022; Stojanowski et al, 2017, 2018, 2019). This pattern implicates overlapping genetic effects in generating symmetrical crown form across left and right sides of the dentition.…”

“…Interestingly, though, moderate to high cross‐field genetic correlations have been reported for humans and tamarins (Hardin, 2019a; Hardin et al, 2022; Stojanowski et al, 2017). These findings suggest the incisor/postcanine modular structure is, in fact, not uniformly conserved across the order Primates.…”

Keeping 21st Century Paleontology Grounded: Quantitative Genetic Analyses and Ancestral State Reconstruction Re-Emphasize the Essentiality of Fossils

“…Even though the fundamental concept of quantitative genetics originated with Mendel, the ability to analyze the inheritance of normal, continuously varying traits across complex pedigrees was not possible until recently, as the algorithms are computationally intense and require modern computing technologies (for a history of approaches to dental variation: [ 40 ]). The modern concepts of evolutionary quantitative genetics were developed almost forty years ago [ 102 , 103 , 104 , 105 ], but it has been over the last 20 years that there has been an incredible expansion of quantitative genetic analyses being applied to evolutionary questions (examples of this research using primate models: [ 38 , 43 , 46 , 47 , 48 , 49 , 100 , 106 , 107 , 108 , 109 , 110 ]).…”

“…For example, minor shape variants on the crown are genetically independent of tooth size [ 41 ]. Looking along the dental arcade, we see that the size of the incisors is genetically independent from the size of the premolars and molars (in baboons [ 42 ]; and macaques [ 43 ]; with some suggestive evidence in humans [ 44 , 45 ]; but see tamarins [ 46 , 47 ], and a different study on humans [ 48 ]), yet there is significant pleiotropy between postcanine teeth [ 42 , 43 , 46 , 47 , 48 ]. Evidence of pleiotropy indicates a genetic correlation, meaning that a significant proportion of the residual phenotypic variance in the two traits is due to the shared additive effects of the same gene or set of genes.…”

“…In baboons, for example, we also discovered that molar width is genetically correlated with body size (with more than 20% of the additive genetic covariance between these traits estimated to be due to the same gene or set of genes), but in surprising contrast, molar length is not [ 49 ]. While this exact correlation has not yet been explored in other primates, variation in crown area for humans has a positive correlation with the length of the dental arch, and a negative correlation with arch width, suggesting that tooth area and size dimensions within human dentitions are similarly not uniform [ 48 ]. Based on this genetic evidence, we now know that variation in the 2D occlusal area (as studied by paleontologists) reflects a range of underlying genetic effects related to body size and sex in addition to the genetic effects that pattern dental variation.…”