Twin Research

Articles

Importance of Genetic Effects for Characteristics of the Human Iris

Mats Larssona1 c1, Nancy L. Pedersena2 and Håkan Stattina3

a1 Department of Behavioral, Social and Legal Sciences, Center for Developmental Research, Örebro University, Sweden. mats.larsson@bsr.oru.se

a2 Department of Medical Epidemiology, Karolinska Institutet, Stockholm, Sweden.

a3 Department of Behavioral, Social and Legal Sciences, Center for Developmental Research, Örebro University, Sweden.

Abstract

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%).

Correspondence:

c1 Address for correspondence: Mats Larsson, Department of Behavioral, Social and Legal Sciences, Center for Developmental Research, Örebro University, 701 82 Örebro, Sweden.

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