A family set method for estimating heredity and stress. II. Preliminary results of the genetic methodology in a pilot survey of Negro blood pressure, Detroit, 1966-1967.

THE PURPOSES of this report are to describe a method to evaluate genetic components of variability using survey techniques, and to present preliminary results from the application of this method to crude measures of skin color and height, and to blood pressure. Most recent evidence suggests that the genetic contribution to the observed variability between individuals in blood pressure, systolic and diastolic, is multifactorial in nature, and that hypertension is merely “one tail” of a continuous distribution [I, 21. While this point of view does not as yet have universal acceptance, meaningful estimates of the genetic contribution must ultimately relate differences in blood pressure to quantifiable genotypic differences irrespective of the number of genes involved or the nature of their action. Fortunately, genetic theory specifies the proportion of independently segregating autosomal genes which various biological relatives will share on the average. Thus, parent and offspring or siblings will share half of their genes in common; fist cousins, one-eighth, and so forth. These proportions may also be interpreted as the probability for any given (autosomal) gene specified in one person that the stated relative will possess the same gene, in the sense of a gene of common origin. These proportions are termed coefficients of relationship, and are clearly measures of genetic similarity. Commonness of origin implies that both genes have been derived from a single ancestral gene. The complements of the aforementioned coefficients may be regarded as measures of genetic dissimilarity or distance from commonness of origin. In this latter view, the average percentage of genes of dissimilar origin between (1) an index case and himself (or herself) is zero, (2) index and his (her) sibling is 50 per cent, (3) index and his (her) first cousin is 87 per cent, (4) index and his (her) spouse is 100 per cent, assuming no biological relationship, and, finally (5) index and his (her) control is