Genetic control of blood neutrophil concentration in the rat

Two phenotypes that characterize low and high neutrophil concentrations in blood were found in the rat. It is possible that either two regulating alleles control the high (Nr-1a) and the low (Nr-1b) neutrophil concentration or that a polygenic system affects the neutrophil concentration in blood. The F1 hybrids of four intercrosses had low neutrophil levels in blood that suggested a dominant effect of the Nr-1b allele. The backcross progeny showed abnormal segregation of the neutrophil phenotypes. The high phenotype was expressed in only 5% of the offspring. The presence of the two phenotypes and their distribution in the backcross progeny was confirmed by the computer program SKUMIX that resolved the quantitative traits into two discrete distributions with 95% and 5% representation. Because the logistic of SKUMIX can not rule out the polygenic effect, only further breeding studies using linked markers can resolve the mechanism of the genetic control of neutrophil concentration in the rat.