X-linked gene expression and sex determination in Caenorhabditis elegans.
The signal for sex determination in the nematode Caenorhabditis elegans is the ratio between the number of X chromosomes and the number of sets of autosomes (the X/A ratio). Animals with an X/A ratio of 0.67 (a triploid with two X chromosomes) or less are males. Animals with an X/A ratio of 0.75 or more are hermaphrodites. Thus, diploid males have one X chromosome and diploid hermaphrodites have two X chromosomes. However, the difference in X-chromosome number between the sexes is not reflected in general levels of X-linked gene expression because of the phenomenon of dosage compensation. In dosage compensation, X-linked gene expression appears to be 'turned down' in 2X animals to the 1X level of expression. An intriguing and unexplained finding is that mutations and X-chromosome duplications that elevate X-linked gene expression also feminize triploid males. One way that this relationship between sex determination and X-linked gene expression may be operating is discussed.
Meneely
P M
PM
Fred Hutchinson Cancer Research Center, Seattle, WA 98104.
D000818:Animals; D002107:Caenorhabditis / Q000235:genetics* / Q000502:physiology; D005260:Female; D015870:Gene Expression; D008297:Male; D012732:Sex Determination Analysis; D014960:X Chromosome