skip to main content

Explore Research Products in the PAR
It may take a few hours for recently added research products to appear in PAR search results.


Title: Mirror, mirror? An evaluation of identical twin mirroring in tooth crown morphology
Abstract

It has been estimated that 25% of monozygotic (“identical”) twin pairs exhibit reverse asymmetry (RA) or “mirroring” of minor anatomical features as a result of delayed zygote division. Here, we examine whether identical twin mirroring accounts for patterns of dental asymmetry in a sample of monozygotic and dizygotic (“fraternal”) twins. We focus on crown morphology to approach the following question: is there an association between dental RA frequency and twin type suggestive of the presence of mirror image twins in our sample? Data were collected from 208 deciduous and 196 permanent dentitions of participants of the University of Adelaide Twin Study using Arizona State University Dental Anthropology System standards. RA frequencies were compared across morphological complexes (deciduous, permanent), twin types (monozygotic, dizygotic), and traits. Fisher's exact tests were performed to formally evaluate the association between twin type and dental RA. Across the entire dataset, RA rates failed to exceed 8% for any twin type. In monozygotic twins, deciduous mirroring totaled 5.3% of observed cases, while permanent mirroring totaled 7.8% of observed cases. We found no statistically significant association between RA and twin type for any morphological character (p‐value range: 0.07–1.00). Our results suggest the timing of monozygotic twin division does not explain the structure of asymmetry for our morphology dataset and that published estimates of identical twin mirroring rates may be inflated or contingent upon phenotype. Instead, rates reported for this sample more closely align with the proposed etiology of this condition.

  more » « less
PAR ID:
10491433
Author(s) / Creator(s):
 ;  ;  ;  
Publisher / Repository:
Wiley Blackwell (John Wiley & Sons)
Date Published:
Journal Name:
The Anatomical Record
ISSN:
1932-8486
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. ; ; ; ; ( , American Journal of Physical Anthropology)
    Abstract Objectives

    This study generates a series of narrow‐sense heritability estimates for crown morphology of the deciduous and permanent dentition with two overarching aims. The first is to test the hypothesis that deciduous teeth provide a more faithful reflection of genetic information than their permanent successors. The second is to use quantitative genetic methods to evaluate assumptions underlying common data collection and analysis practices in biodistance research.

     Materials and Methods

    Dental morphology data were collected from longitudinal dental casts representing Australian twins and families using Arizona State Dental Anthropology System standards. Polygenic models and estimates of narrow‐sense heritability were generated using SOLAR v.8.1.1. Each model considered age, sex, and age/sex interaction as covariates.

     Results

    Heritability estimates significantly differed from zero for the majority of morphological crown characters. Most estimates fell within the 0.4–0.8 range typically observed for crown morphology. Mean heritability was stable across the dental complex, but for paired homologues, permanent traits often yielded higher estimates than their deciduous counterparts. Results indicate directional asymmetry in environmental influence for crown morphology and inform biodistance “best practices” related to data collection and treatment.

     Conclusions

    Overall, results for this sample support the use of crown morphology as a proxy for genetic variation in evolutionary research. This includes the deciduous dentition, which justifies the expansion of efforts to incorporate subadults into reconstructions of past microevolutionary processes. Results do not indicate that deciduous phenotypes more closely approximate underlying genotype, at least for deciduous/permanent homologues.

     
    more » « less
  2. ; ; ; ; ; ( , The Journal of Neuroscience)

    How variable is the functionally defined structure of early visual areas in human cortex and how much variability is shared between twins? Here we quantify individual differences in the best understood functionally defined regions of cortex: V1, V2, V3. The Human Connectome Project 7T Retinotopy Dataset includes retinotopic measurements from 181 subjects (109 female, 72 male), including many twins. We trained four “anatomists” to manually define V1-V3 using retinotopic features. These definitions were more accurate than automated anatomical templates and showed that surface areas for these maps varied more than threefold across individuals. This threefold variation was little changed when normalizing visual area size by the surface area of the entire cerebral cortex. In addition to varying in size, we find that visual areas vary in how they sample the visual field. Specifically, the cortical magnification function differed substantially among individuals, with the relative amount of cortex devoted to central vision varying by more than a factor of 2. To complement the variability analysis, we examined the similarity of visual area size and structure across twins. Whereas the twin sample sizes are too small to make precise heritability estimates (50 monozygotic pairs, 34 dizygotic pairs), they nonetheless reveal high correlations, consistent with strong effects of the combination of shared genes and environment on visual area size. Collectively, these results provide the most comprehensive account of individual variability in visual area structure to date, and provide a robust population benchmark against which new individuals and developmental and clinical populations can be compared.

    SIGNIFICANCE STATEMENTAreas V1, V2, and V3 are among the best studied functionally defined regions in human cortex. Using the largest retinotopy dataset to date, we characterized the variability of these regions across individuals and the similarity between twin pairs. We find that the size of visual areas varies dramatically (up to 3.5×) across healthy young adults, far more than the variability of the cerebral cortex size as a whole. Much of this variability appears to arise from inherited factors, as we find very high correlations in visual area size between monozygotic twin pairs, and lower but still substantial correlations between dizygotic twin pairs. These results provide the most comprehensive assessment of how functionally defined visual cortex varies across the population to date.

     
    more » « less
  3. ; ; ; ( , Behavioral Disorders)

    Valid and reliable teacher ratings serve as the foundation for screening and assessment of youth with behavioral disorders and twin studies offer an opportunity to study those ratings. We conducted a meta-analysis of 15 empirical investigations of aggressive and rule-breaking behavior using teacher ratings in the context of a twin research design. We retrieved n = 53 correlations from n = 7,885 pairs of monozygotic (MZ) twins and n = 67 correlations from n = 11,696 pairs of dizygotic (DZ) twins with two goals: (a) to test the best-fitting models for predicting similarity (correlations) in teacher ratings of MZ and DZ twin pairs and (b) to identify significant predictors in the respective models. We found that, for both MZ and DZ twins, the best-fitting model included all predictors and interactions. In the MZ model, we found a significant positive interaction between the percentage of same teachers who completed the ratings and male twins; in the DZ model, we found a significant negative interaction between the percentage of same teachers who completed the ratings and opposite sex twins. Teacher ratings converged and diverged in expected ways, advancing research in the context of the attributions-bias-context (ABC) model of informant ratings.

     
    more » « less
  4. ; ; ; ; ; ; ; ( , International Journal of Eating Disorders)
    Abstract Background

    COVID‐19 was associated with significant financial hardship and increased binge eating (BE). However, it is largely unknown whether financial stressors contributed to BE during the pandemic. We used a longitudinal, cotwin control design that controls for genetic/environmental confounds by comparing twins in the same family to examine whether financial hardship during COVID‐19 was associated with BE.

     Methods

    Female twins (N = 158;Mage = 22.13) from the Michigan State University Twin Registry rated financial stressors (e.g., inability to afford necessities) daily for 49 consecutive days during COVID‐19. We first examined whether financial hardship was associated with BE phenotypes across the full sample. We then examined whether cotwins who differed on financial hardship also differed in BE.

     Results

    Participants who experienced greater mean financial hardship across the study had significantly greater dimensional BE symptoms, and participants who experienced greater financial hardship on a given day reported significantly more emotional eating that day. These results were replicated in cotwin control analyses. Twins who experienced more financial hardship than their cotwin across the study reported greater dimensional BE symptoms than their cotwin, and participants who experienced more financial hardship than their cotwin on a given day reported greater emotional eating that day. Results were identical when restricting analyses to monozygotic twins, suggesting associations were not due to genetic confounds.

     Conclusions

    Results suggest that BE‐related symptoms may be elevated in women who experienced financial hardship during COVID‐19 independent of potential genetic/environmental confounds. However, additional research in larger samples is needed.

     Public Significance

    Little is known regarding how financial difficulties during the COVID‐19 pandemic may have contributed to increased binge eating (BE). We found preliminary evidence that financial hardship during COVID‐19 may be associated with greater rates of BE‐related symptoms even when comparing twins from the same family. While additional research is needed, results suggest that people who experienced financial hardship during COVID‐19 may be at increased risk for BE.

     
    more » « less
  5. ; ; ; ; ; ( , Palaeontological Association Annual Meeting)
    Taeniodonta is a group of North America Palaeogene mammals that lived after the end-Cretaceous mass extinction. Taeniodonts show an extreme degree of dental wear, indicative of an abrasive diet, leading to hypsodonty in the most derived species. The rarity of fossils and their highly worn teeth makes their dental morphology difficult to study. We examined five new partial mandibles from the San Juan Basin, New Mexico, USA, most of which preserve unworn molars. One of the specimens preserves a deciduous ultimate premolar and using 3D micro-CT we were able to segment and study the unworn permanent tooth embedded in the jaw. We then conducted multivariate analyses on dental measurements to compare the new specimens to known teeth of early taeniodonts. We assigned the new specimens to at least three genera of Conoryctidae, a taeniodont subclade. Our results suggest that there is a broader dental diversity of the studied genera than previously thought. Morphological observations also suggest that progressive loss of cingulids and the addition of cuspids started early in the evolution of taeniodonts. These distinctive dental specializations strengthen the hypothesis that early Palaeocene mammals were able to rapidly adapt to fill the vacant ecological niches after the end-Cretaceous extinction 
    more » « less
  • Citation Formats
  • MLA
  • APA
  • Chicago
  • BibTeX
  • Save / Share this Record
  • Send to Email