Aspects of the tabby—crinkled—downless syndrome

Two alleles of the sex-linked gene tabby, Ta and Ta°, and two autosomal mimics of tabby, crinkled, cr, and downless, dl, each produce a similar mutant syndrome involving the coat and dentition of the mouse. Certain aspects of the development of the mutant defects have already been studied, and some comparisons between tabby and crinkled have been made. The present investigation is concerned with a comparison of all four genes, and with further analysis of the developmental basis for the dental abnormalities. As the expression of a mutant gene can be modified considerably by genetic background, critical comparison between genes with similar effects requires a common genetic environment. The four genes under consideration here were crossed twice from their stock backgrounds to two standard inbred strains. Conclusions were then drawn from the reactions of characters scored to background change, rather than from the absolute level of expression in any one background. Comparative information about the genes was derived from a consideration of the relative reaction of each character between genes, and inferences as to the developmental basis for some of the dental abnormalities were drawn from the relative reactions of different characters over all genes. In addition, a combination of within and between gene comparisons gave some indication of the level at which background modification was operating. Also, the wide range of expression of the syndrome produced by the four genes in different genetic backgrounds was itself useful in the developmental analysis.