GENETICAL STUDY ON THE JAPANESE CROOKED-TAIL IN THE MOUSE

Abstract

The Japanese crooked-tail which frequently appeared sporadically in the Japanese laboratory mice named Kasukabe group was analysed genetically. Sporadic appearance of this abnormality, a clear selection response to increasing frequency of appearance, and an easy establishment of crooked stock in which the frequency was always beyond 90%, made us assume that this genetic abnormality was controlled by a number of polygene pairs none of which had major effect. This assumption was confirmed by the results of experiments comprised of outcrossing the crooked strain with other strains and successive backcrosses of normal segregants to the crooked individuals from the crooked strain; in this mating experiment the frequency of occurrence of crooked abnormality increased markedly from generation to generation. Furthermore, the result of “outcross, high selection and between-line cross” experiments showed that the expression of crooked phenotype did not necessitate a complete accumulation of the polygenes responsible and that the polygenes were in general of recessive nature. From these observations the authors considered that the Japanese crooked-tail was a kind of genetic variation similar in its genetic basis to LERNER's “phenotypic deviants (phenodeviants)” and GRÜNEBEG's “quasi-continuous variations.”.
From the analysis of results of successive backcross experiment and mathematical formulation, it could be considered that the number of crooked polygene loci being maintained in the crooked strain and so segregating in successive backcross lines was at least 3 larger than the minimum number of polygene loci fixed for expression of the tail abnormality. This meant that the existence of crooked polygenes had been of fairly ubiquitous nature in the Japanese Kasukabe group of mice.