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Human iris characteristics as biomarkers for personality
Örebro University, Department of Behavioural, Social and Legal Sciences.
2007 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This dissertation explains why behavioral genetic research can be better informed by using characteristics in the human iris as biomarkers for personality, and is divided into five parts. Part I gives an introduction to the classical twin method and an overview of the findings that have led most developmental researchers to recognize that the normal variation of personality depends on a complex interplay between genetic and environmental factors. Part II highlights empirical findings that during the last twenty years have gradually moved genetic and environmental theory and research to evolve toward one another, and also presents the theory of genetics and experience that currently is used to explain how the interplay between genes and the environment works. Part III explains why, from a developmental perspective, it is of interest to identify candidate genes for personality, and gives a brief overview of genes that have been associated with personality. Problems associated with genetic research on the molecular level and how these apply to personality are also highlighted. Part IV examines molecular research on the iris and the brain, which suggests that genes expressed in the iris could be associated with personality, and explains how the use of iris characteristics can increase power to test candidate genes for personality by taking advantage of the self-organizing properties of the nervous system. The empirical foundation for the questions posed in this dissertation and also the empirical results are presented here. Part V discusses the associations found between iris characteristics and personality, and exemplifies how iris characteristics can be used within the theoretical frameworks presented in parts I, II, III and IV. In other words, Part V explains how iris characteristics – in addition to identify as well as test candidate genes for personality – can be used to investigate how people’s experiences in themselves are influenced by genetic factors.

Place, publisher, year, edition, pages
Örebro: Örebro universitet , 2007. , p. 128
Series
Örebro Studies in Psychology, ISSN 1651-1328 ; 12
Keywords [en]
Personality, iris characteristics/crypts/pigment dots/contraction furrows, candidate genes MITF/PAX6/SIX3/LMX1B/FOXC1/FOXC2/PITX2/BMP4/OLFM3/ MSX1/MSX2, anterior cingulate, genetic correlations, heritability, hemispheric asymmetries, approach-related behaviors
National Category
Psychology
Research subject
Psychology
Identifiers
URN: urn:nbn:se:oru:diva-1684ISBN: 978-91-7668-562-4 (print)OAI: oai:DiVA.org:oru-1684DiVA, id: diva2:135317
Public defence
2007-12-14, Hörsal L 3, Långhuset, Örebro universitet, Örebro, 13:00
Opponent
Supervisors
Available from: 2007-11-23 Created: 2007-11-23 Last updated: 2017-10-18Bibliographically approved
List of papers
1. Importance of genetic effects for characteristics of the human iris
Open this publication in new window or tab >>Importance of genetic effects for characteristics of the human iris
2003 (English)In: Twin research, ISSN 1369-0523, E-ISSN 2053-6003, Vol. 6, no 3, p. 192-200Article in journal (Refereed) Published
Abstract [en]

The relative importance of genetic influences (heritability) on five general textural quality characteristics of the human iris was assessed using sex and age limitation models. Colour photographs of irises were available from 100 monozygotic twin pairs, 99 dizygotic twin pairs, and 99 unrelated randomly paired age-matched German subjects. Comparative scales were constructed and two judges who were blind to zygosity independently rated five characteristic of the subjects' left iris. Inter-rater reliabilities were larger than .90 for all five scales. The heritabilities for the five iris characteristics ranged from .51-.90. No sex-specific genetic factors were found for the iris characteristics. Age-group differences in heritability were found for one of the five iris characteristics — "distinction of white dot rings". Heritability was greater for the older cohort (90%) than the younger (73%). The iris characteristics that showed the next highest additive-genetic effect were "contractional furrows" (78%) and "frequency of crypts" in the main stroma leaf (66%).

National Category
Psychology
Research subject
Psychology
Identifiers
urn:nbn:se:oru:diva-2856 (URN)10.1375/136905203765693843 (DOI)
Available from: 2007-11-23 Created: 2007-11-23 Last updated: 2017-12-14Bibliographically approved
2. Genetic correlations among texture characteristics in the human iris
Open this publication in new window or tab >>Genetic correlations among texture characteristics in the human iris
2004 (English)In: Molecular Vision, ISSN 1090-0535, E-ISSN 1090-0535, Vol. 10, p. 821-831Article in journal (Refereed) Published
Abstract [en]

PURPOSE:

To estimate the magnitude of genetic correlations among five general textural characteristics of the human iris.

METHODS:

Color photographs of iris were available from 100 monozygotic and 99 dizygotic twin pairs. Comparative scales were constructed based on ratings of the subjects' left iris. To explore the genetic and environmental covariation among frequency of Fuchs' crypts, frequency of pigment dots, iris color, the extension, and distinction of Wolfflin nodules, and contraction furrows, a structural equation model with Cholesky decomposition was applied to variance-covariance matrices for monozygotic (MZ) and dizygotic (DZ) pairs.

RESULTS:

Significant genetic correlations fell between -0.22 and 0.44 and accounted almost entirely for the phenotypic correlations among the iris characteristics. No evidence for individual specific environmental effects in common to the characteristics was found.

CONCLUSIONS:

The modest genetic correlations indicate that there is little overlap in the genetic influence for these characteristics. Candidate genes with embryological and histological expression patterns in the eye could potentially influence the iris characteristics' variability.

National Category
Psychology
Research subject
Psychology
Identifiers
urn:nbn:se:oru:diva-2857 (URN)
Available from: 2007-11-23 Created: 2007-11-23 Last updated: 2017-12-14Bibliographically approved
3. Associations between iris characteristics and personality in adulthood
Open this publication in new window or tab >>Associations between iris characteristics and personality in adulthood
2007 (English)In: Biological Psychology, ISSN 0301-0511, E-ISSN 1873-6246, Vol. 75, no 2, p. 165-175Article in journal (Refereed) Published
Abstract [en]

Variable and person-oriented analyses were used to explore the associations between personality and three previously untested general iris characteristics: crypts, pigment dots and contraction furrows. Personality data, as measured by the NEO PI-R and ratings of iris characteristics from 428 undergraduate students were collected. Crypts were significantly associated with five approach-related behaviors, i.e., feelings, tendermindedness, warmth, trust and positive emotions, whereas furrows were associated with impulsiveness. These findings suggest that because Pax6 induces tissue deficiencies in both the iris and the left anterior cingulate cortex, Pax6 may influence the extent people engage in approach-related behaviors. The results from using a person-oriented analysis suggested that people with different iris configurations tend to develop along different personality trajectories. Future longitudinal studies, twin-studies and genetic association studies, may benefit from collecting iris data and testing candidate genes for crypts and furrows

National Category
Psychology
Research subject
Psychology
Identifiers
urn:nbn:se:oru:diva-2858 (URN)10.1016/j.biopsycho.2007.01.007 (DOI)
Available from: 2007-11-23 Created: 2007-11-23 Last updated: 2017-12-14Bibliographically approved

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