The joy of balancers

Abstract

Balancer chromosomes are multiply inverted and rearranged chromosomes that are widely used in Drosophila genetics. First described nearly 100 years ago, balancers are used extensively in stock maintenance and complex crosses. Recently, the complete molecular structures of several commonly used balancers were determined by whole-genome sequencing. This revealed a surprising amount of variation among balancers derived from a common progenitor, identified genes directly affected by inversion breakpoints, and cataloged mutations shared by balancers. These studies emphasized that it is important to choose the optimal balancer, because different inversions suppress meiotic recombination in different chromosomal regions. In this review, we provide a brief history of balancers in Drosophila, discuss how they are used today, and provide examples of unexpected recombination events involving balancers that can lead to stock breakdown.

Mutations of γCOP Gene Disturb Drosophila melanogaster Innate Immune Response to Pseudomonas aeruginosa

“…Herein, the term “normality” refers only to the natural linkage order of the genes, but not to alleles and or to other small-scale mutations. A balanced chromosome is actually a haploblock, which keeps in cis configuration not only the lethal recessive alleles, but also other known or hidden mutations, considering that the balancer is not leaky [ 31 ]. TM6B contains the spontaneous inversion In(3R)C, which is also present in many natural populations but not in the Oregon strain [ 26 ].…”

“…Detailed data concerning the multiple inversions’ effects on the expression of genes located in fruit fly balancer chromosomes were reported [ 32 ]. Misexpression of genes is determined either by their proximity to breakpoints of inversion or because they are physically disrupted by the inversions [ 31 ].…”

How to turn an organism into a model organism in 10 ‘easy’ steps

“…Techniques that think 'outside the microinjection box', like ReMOT control (Chaverra-Rodriguez et al, 2018), will be extremely helpful for opening up genome editing in new species where it can be difficult to collect or inject eggs. Drosophila genetics has benefited enormously from the availability of balancer chromosomes that suppress recombination (Miller et al, 2019). The general availability of balancer chromosomes in other species would dramatically speed up genetic manipulation because they allow investigators to stabilize mutations and maintain and follow transgenic lines without molecular genotyping.…”

Digest: Female‐limited X chromosome evolution in Drosophila melanogaster *

“…In this issue, Lund‐Hansen and colleagues (2020) investigate female‐limited X chromosome (FLX) evolution in Drosophila melanogaster , where male sexual antagonism is eliminated by enforcing matrilineal inheritance of the X chromosome using a balancer chromosome. Balancer chromosomes are engineered to contain recessive lethal mutations to prevent homozygosity of the balancer chromosome, translocations and inversions to prevent meiotic recombination events (Figure 1), and dominant visible markers to track their presence (reviewed in Miller et al., 2019). These balancer chromosomes are often used to maintain the presence and fidelity of a corresponding homologous chromosome of interest in a population.…”