A chromosome carrying a balancer region is termed as a balancer chromosome. A balancer is a region which prevents recombination between homologous chromosomes during meiosis. This is possible due to the presence of an inverted region or a series of inversions. Balancer chromosome was primarily used for studies in "Drosophila melanogaster" genetics. Monica Justice "et al." (2009) efficiently carried out a balancer screen using a balancer chromosome constructed by Allan Bradley "et al." on mouse chromosome 11. In this screen, an ENU-induced male is crossed with a female heterozygous for the balancer chromosome. The mice carrying the balancer chromosome have yellow ears and tail. The G1 heterozygotes are (Figure 5) are crossed to females carrying the rex mutation ("Rex" in figure 5), which confers a curly coat. In G2, homozygotes for the balancer are non-viable and are not recovered. Mice carrying the rex mutation trans to the balancer or ENU-induced mutation have a curly coat and are discarded. The ENU mutant + rex mutant mice are discarded in order to prevent recombination between those two chromosomes during the next breeding step, which is generating homozygous mutants. Mice that are compound heterozygotes for the balancer and the ENU-induced mutation are brother-sister mated to obtain homozygotes for the ENU-induced mutation in G3.