Each balancer chromosome carried a particular set of dominant and recessive mutations when it was initially isolated. We call the original combination of inversions and marker mutations the “core balancer”. Subsequently, variant versions were often isolated with new marker mutations or transgenes. The list below provides the full genetic constitution of each core balancer used in Bloomington genotypes.

In genotypes, we list the core balancer symbol plus any variant markers with one exception -we list Tb[1] in TM6B genotypes even though it was present on the original TM6B chromosome because Tb[1] reverts at a high frequency. Many TM6B chromosomes now carry a Tb[+] allele.

FlyBase provides a single symbol for each balancer variant. For example, CyO-vAb represents the CyO core balancer plus the additional bw[1] marker. These single symbols are not used in Bloomington genotypes; instead, we list the variant markers explicitly.

The list below provides the full genetic constitution of each balancer symbol used in the Bloomington stock list. The balancer symbol links to a list with the rearrangement breakpoints of each balancer.