Balancer chromosome

A balancer chromosome is a particular chromosome that is different genetic research with Drosophila melanogaster of the other organisms, and it gives a significant advantage. The balancer chromosome prevents the recombination ( crossing over the ) can be kept as stable stocks in the fly, so that recessive lethal mutations. Balancer chromosomes thus use the mechanism of the balanced polymorphism.

The idea of ​​balancer chromosomes goes back to Hermann Joseph Muller, who discovered in 1918 that the chromosome C1B suppressed recombination on the X chromosome. He found that this chromosome is no longer able by various inversions to take Homologous recombination with the sister chromosome. When these chromosomes are combined with a recessive markers, they represent a very useful tool in the fly genetics dar. In Stocks with such a balancer chromosome can only survive such flying, carrying a balancer chromosome and on the other chromosome, the recessive lethal mutation. Were it not for these chromosomes, each new generation would have to be selected on their genotype, to ensure that the mutation is not lost.

Balancer there for chromosomes X, 2 and 3 are the most efficient balancer chromosomes that suppress recombination over the entire length of the chromosome. In cases in which still a cross-over occurs, incorrect chromosomes are generated, as in the resulting germ cells a large part of a chromosome is duplicated or deleted.

For X -chromosomal balancer one exception: since the hemizygous males would not survive a recessive lethal markers, because they do not have a healthy X chromosome, but instead the Y chromosome, the X chromosome, for example, markers are used that do not lethal but only have a sterile female phenotype. Then female flies can develop, which carry a Doppelbalancer, but they can not reproduce.