FlyBase supports three different ways of representing balancer chromosomes in genotypes, two of which are used in the Bloomington stock list.

1. Balancer symbol

A single symbol represents a unique set of aberrations and markers.

2. Balancer short genotype

A balancer symbol is combined with aberration, transposon and allele symbols to describe a unique balancer variant.

3. Balancer full genotype

All aberration, transposon and allele symbols that comprise the unique balancer variant are explicitly stated.

The Bloomington stock list uses balancer symbols for the core set of balancers described in Lindsley & Zimm (1992) plus a few others and balancer short genotypes for all other balancer chromosomes. Thus, only aberrations, insertions and alleles that vary from those defined by the balancer symbol are shown in genotypes. An exception is made for TM6B balancers that expressed Tb¹ at one time but no longer do so; in these cases Tb⁺ is explicit in the genotype.

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.