Researchers have uncovered a mechanism that safeguards the biallelic expression of haploinsufficient genes, shedding light on the importance of having two copies of each chromosome. A study identified the epigenetic regulator MSL2 an ‘anti-monoallelic’ factor that maintains biallelic gene dosage. This discovery not only reveals a communication system between parental alleles but also points to potential therapeutic strategies for diseases associated with haploinsufficient genes.