M. F. Lyon
MRC Radiobiology Unit, Harwell, Didcot, Oxford OXI 1 ORD, UK
The mammalian system of sex determination, in which the presence of a Y chromosome determines maleness, irrespective of the number of X chromosomes, appears fundamentally different from systems depending on X: autosome balance found in Drosophila and various other organisms. However, there are some similarities. In mammalian germ cells, the correct X-chromosome dosage (single in male and double in female) appears essential for cell survival. In the somatic cells, the number of active X chromosomes appears to depend on the number of autosomal sets, i.e. in triploids and tetraploids more than one X may remain active. The X chromosome is known to carry genes involved in sex determination and differentiation. The relationship between X-chromosome inactivation and sex determination is discussed.
A. Weith1, H.-J. Paust1, H. Winking2 and C. Bishop1
1Institut...