Additive genetic variation of transcriptional regulation: metallothionein expression in the soil insect Orchesella cincta.

Field-selected metal tolerance in Orchesella cincta is correlated with overexpression of the single copy cadmium (Cd) inducible metallothionein (mt). Previously, we have demonstrated large phenotypic variation in mt gene expression, and a higher frequency of high-expression phenotypes in a tolerant population. Here, we describe midparent-offspring regression analysis of mt gene expression in a laboratory culture originating from a noncontaminated natural population. Families were either not exposed (n = 47) or exposed to 0.5 μmol Cd per gram dry food (n = 46). Mean mt gene expressions normalized to 28S rRNA and β-actin RNA were generated using real-time RT-PCR applied to parents and offspring RNA and subjected to regression analysis. A significant heritability (h