High Quality Content by WIKIPEDIA articles! Balancer Chromosomes are special, modified chromosomes used for genetically screening a population of organisms to select for heterozygotes. Balancer chromosomes can be used as a genetic tool used to prevent crossing over (genetic recombination) between homologous chromosomes during meiosis. Balancers are most often used in Drosophila melanogaster (fruit fly) genetics to allow populations of flies carrying heterozygous mutations to be maintained without constantly screening for the mutations but can also be used in mice. Balancer chromosomes have three important properties: they suppress recombination with their homologs, carry dominant markers, and negatively affect reproductive fitness when carried homozygously.