Autosomal Insertion Research Articles

Cytological Study of an X-Autosome Translocation in <i>Mus musculu</i><i>s</i>

Earlier genetic studies on this stock of mice with an X-autosome translocation revealed that wild-type alleles of <i>pink-eye </i>and <i>chinchilla </i>of linkage group I have been translocated to the X. When the X<sup>t</sup> was accompanied by an X<sup>n</sup>, animals heterozygous for <i>pp </i>and <i>c</i><sup>ch</sup><i>c</i><sup>ch</sup> showed variegated coat colors but the X<sup>t</sup> alone led only to the wild-type coat color. The cytological investigation reported herein revealed the following information: 1. The translocation was non-reciprocal. About one third of the autosome representing linkage group I was transposed into the X, making the X<sup>t</sup> about 20% longer than the X<sup>n</sup>. 2. The autosomal insertion behaved as an integral part of the X, manifesting positive heteropyenosis when the X itself assumed this condition. 3. In the skin of animals with a variegated phenotype, the <i>cc </i>patches were apparently populated by cells containing a condensed X<sup>t</sup>, while in wild-type patches from the same animal, the X<sup>t</sup> was isopyenotic, behaving in the same manner as the euchromatic autosomes. These findings support Lyon’s hypothesis explaining the somatic variegation in <i>Mus musculus </i>due to X-autosome translocation (1961, 1962). The present study on skin cells of X<sup>t</sup>X<sup>n</sup> females has yielded convincing evidence that the mammalian female is indeed a natural mosaic.