Mutant for female meiotic segregation: 1.6% X chromosome exceptions from X/X females. 2.2% 4th chromosome exceptions from X/X females. 10.0% X chromosome exceptions from X/Bal females. 7.8% 4th chromosome exceptions from X/Bal females. Primarily affects achiasmate chromosome segregation. X and 4th chromosome nondisjunctions occur apparently independently of one another. Exchange is normal.