Genetic and environmental components of thyroxine variation in Mennonites from Kansas and Nebraska

Thyroxine is an endocrine hormone that regulates cellular and organismic metabolism. Current research on thyroxine has primarily examined its adaptive potential and genetic inheritance patterns. To date, no studies have attempted to investigate the interaction between the genetic and environmental components of thyroxine variation. This approach is useful because hormones are on feedback regulation; thus interaction occurs between the environment and gene expression. The purposes of this research are to characterize the genetic and environmental components of thyroxine variation using univariate statistics and to estimate the genetic and cultural heritabilities through path analysis. For univariate analyses, analyses of variance are used to determine whether or not age, sex, or community affiliation are covariates of thyroxine level. Significant differences existed in thyroxine level based on sex and community affiliation (p < 0.05). The genetic and environmental components of thyroxine variation were partitioned through path analysis. Heritability was estimated at 0.317 +/- 0.109 for the genetic component and at 0.060 +/- 0.029 for the environmental component. The environmental variables that contributed to the variation in thyroxine level were caffeine consumption, blood calcium level, and biceps skinfold thickness.