THE INHERITANCE OF FACTORS ASSOCIATED WITH JOINT MOBILITY

From a sample of 1,500 individuals belonging to 442 migrant nuclear fa milies from northeastern Brazil, information on the interphalangial mo bility was obtained: (a) the grades of extension of both the right and left thumbs and (b) the angle (in degrees) formed by the distant and proximal phalanx of the thumb. The first principal component of these variables was estimated and called ''extensibility'' A negative associ ation of extensibility and age, as well as with inbreeding, was detect ed. Complex segregation analysis was applied to extensibility and both a multigenic mechanism and an extra transmissible component were dete cted. Mendelian inheritance was rejected, while a model with multifact orial inheritance, together with a factor that is inherited with a tra nsmission probability different from 1/2 (tau = 0.63), was not rejecte d. These findings were supported by path analysis, which showed an imp ortant biologic inheritance (h(2) = 0.675) and the existence of a smal l but significant cultural component (c(2) = 0.003). The observed ''in breeding'' effect, therefore, could not be attributed to a genetic mec hanism and probably is the effect of concomitant environmental variabi lity. (C) 1996 Wiley-Liss, Inc.