AbstractThe upregulation of the JIL‐1 kinase on the male X chromosome and its association with the male‐specific lethal (MSL) complex suggest that JIL‐1 may play a role in regulating dosage compensation. To directly test this hypothesis we measured eye pigment levels of mutants in the X‐linkedwhitegene in an allelic series ofJIL‐1hypomorphic mutants. We show that dosage compensation ofwaalleles that normally do exhibit dosage compensation was severely impaired in theJIL‐1mutant backgrounds. As a control we also examined a hypomorphicwhiteallelewethat fails to dosage compensate in males due to apogoelement insertion. In this case the relative pigment level measured in males as compared to females remained approximately the same even in the most severeJIL‐1hypomorphic background. These results indicate that proper dosage compensation of eye pigment levels in males controlled by X‐linkedwhitealleles requires normal JIL‐1 function. genesis 43:213–215, 2005. © 2005 Wiley‐Liss, Inc.