Expression of a sex-linked gene in standard and fusion-chimeric mice

✍ Scribed by Dunn, G. R.

• Publisher: John Wiley and Sons
• Year: 1972
• Tongue: English
• Weight: 999 KB
• Volume: 181
• Category: Article
• ISSN: 0022-104X
• DOI: 10.1002/jez.1401810102

✦ Synopsis

The single-active-X hypothesis states that in any mammal with more than one X chromosome per cell, only one X is active in each cell. The hypothesis furrher states that X-chromosome differentiation occurs randomly in each cell early in development and subsequently is stable. The phenotype of a mammal heterozygous for a sex-linked gene will thus be mosaic, and any interaction of different X alleles can occur only on the intercellular level. Another hypothesis, the "complemental-X" hypothesis, explains the phenotype of a sexlinked gene heterozygote in terms of intracellular allelic interaction.

The validity of intercellular interaction in sex-linked gene heterozygotes was tested in the mouse by making fusion chimeras of embryos carrying different X-linked alleles and comparing the chimeric phenotype to that of a standard he terozy gote.

The X-chromosome marker Greasy (Gs) was shown to affect ten parameters of hair structure, four of which were chosen to establish a series of hair types.

It was found that Gs/ + mice had almost the entire range of hair types, while wild-type and Gs mice showed restricted hair type distributions, significantly different from each other and from Gs/ + . It was also found that the Gs/+ phenotype could not be accounted for by additivity of the wild-type and mutant hair-type distributions.

Some of the fusion chimeras had phenotypes similar, if not identical, to that of standard Gs/+ mice in all respects except the rate of change in the distribution of hair types with age. This discrepancy could be accounted for on the basis of cell selection. These data support the conclusion that intercellular interaction can account for the observed phenotypes of sex-linked gene heterozygotes.