INFLUENCE OF SEX AND PHENOTYPE OF PARENTS ON THE INCIDENCE OF DIABETES IN BB OK RAT LITTERS

Because diabetes incidence (in the context of animal diabetes defined as percentage of animals developing diabetes until the age of 200 days ) in BB rats is largely the same in males and females, a sex-influence d or sex-linked inheritance of diabetes has been excluded. However, in crossing studies using diabetic rats of the BB/OK rat subline and dif ferent diabetes-resistant rat strains, an excess of females was freque ntly observed, generally connected with an excess of diabetic males. T herefore the incidence of diabetes in 12 litters of [(dBB x DA)F1 x dB B] first backcross hybrids (BC1) and in 331 litters of BB/OK rats was analyzed according to sex ratio of litters and phenotype of parents (d -diabetic, nd-nondiabetic). In BC1 hybrids and BB/OK rats, about 50 % of litters with an excess of females were observed, but an excess of d iabetic males was established only in BC1 hybrids. However, in BB/OK r ats correlations were found between diabetes incidence and litters wit h 1:1 proportion of diabetic males to females (r = -0.42 p < 0.05), ph enotype of parents d x d (r = 0.73 p < 0.01) and nd x nd (r = -0.69 p < 0.01). Furthermore, an indirect influence is observable from correla tions between the phenotype of parents d x d and litters with an exces s of males (r = -0.40 p < 0.05) and diabetic females (r = -0.42 p < 0. 05) as well as litters with a 1:1 proportion of diabetic males and fem ales (r = -0.42 p < 0.05). It is concluded that diabetes in BB/OK rats is most probably incompatible with a ''biologically normal'' sex prop ortion in litters and that a sex-related inheritance appears to exist.