Broad and narrow heritabilities of quantitative traits in a founder population

Estimation of the components of variance for a quantitative trait allows on e to evaluate both the degree to which genetics influences the trait and th e trait's underlying genetic architecture. For particular traits, the estim ates also may have implications for discriminating between potential models of selection and for choosing an appropriate model for linkage analysis. U sing a recently developed method, we estimate the additive and dominance co mponents of variance-or, equivalently, the narrow and broad sense heritabil ities-of several traits in the Hutterites, a founder population with extens ive genealogical records. As a result of inbreeding and because Hutterite i ndividuals are typically related through multiple lines of descent, we expe ct that power to detect dominance variance will be increased relative to th at in outbred studies. Furthermore, the communal lifestyle of the Hutterite s allows us to evaluate the genetic influences in a relatively homogeneous environment. Four phenotypes had a significant dominance variance, resultin g in a relatively high broad heritability. We estimated the narrow and broa d heritabilities as being, respectively, .36 and .96 for LDL, .51 and 1.0 f or serotonin levels, and .45 and .76 for fat free mass (FFM). There was no significant additive component for systolic blood pressure (SBP), resulting in a narrow heritability of 0 and a broad heritability of .45. There were several traits for which we found no significant dominance component, resul ting in equal broad and narrow heritability estimates. These traits and the ir heritabilities are as follows: HDL, .63; triglycerides, .37; diastolic b lood pressure, .21; immunoglobulin E,.63; lipoprotein( a), .77; and body-ma ss index, .54. The large difference between broad and narrow heritabilities for LDL, serotonin, FFM, and SBP are indicative of strong dominance effect s in these phenotypes. To our knowledge, this is the first study to report an estimate of heritability for serotonin and to detect a dominance varianc e for LDL, FFM, and SBP.