like ▁humans , ▁the ▁Y ▁chrom os ome ▁does ▁not ▁confer ▁mal eness ; ▁rather , ▁it ▁enc odes ▁gen es ▁necessary ▁for ▁making ▁s perm . ▁Sex ▁is ▁instead ▁determined ▁by ▁the ▁ratio ▁of ▁X ▁chrom os om es ▁to ▁aut os om es . ▁Furthermore , ▁each ▁cell ▁" dec ides " ▁whether ▁to ▁be ▁male ▁or ▁female ▁independently ▁of ▁the ▁rest ▁of ▁the ▁organ ism , ▁resulting ▁in ▁the ▁occas ional ▁occurrence ▁of ▁g yn and rom orph s . ▁ ▁Three ▁major ▁gen es ▁are ▁involved ▁in ▁determ ination ▁of ▁D ros oph ila ▁sex . ▁These ▁are ▁sex - le th al , ▁sister less , ▁and ▁dead pan . ▁Dead pan ▁is ▁an ▁aut os om al ▁gene ▁which ▁in hib its ▁sex - le th al , ▁while ▁sister less ▁is ▁carried ▁on ▁the ▁X ▁chrom os ome ▁and ▁in hib its ▁the ▁action ▁of ▁dead pan . ▁An ▁A AX ▁cell ▁has ▁twice ▁as ▁much ▁dead pan ▁as ▁sister less , ▁so ▁sex - le th al ▁will ▁be ▁in hib ited , ▁creating ▁a ▁male . ▁However , ▁an ▁AA XX ▁cell ▁will ▁produce ▁enough ▁sister less ▁to ▁in hib it ▁the ▁action ▁of ▁dead pan , ▁allowing ▁the ▁sex - le th al ▁gene ▁to ▁be ▁trans cribed ▁to ▁create ▁a ▁female . ▁ ▁Later , ▁control ▁by ▁dead pan ▁and ▁sister less ▁disapp ears ▁and ▁what ▁becomes ▁important ▁is ▁the ▁form ▁of ▁the ▁sex - le th al ▁gene . ▁A ▁secondary