Balancer Chromosome - Important Scientific Contributions Using Balancer Chromosomes

Important Scientific Contributions Using Balancer Chromosomes

Balancer chromosomes already give geneticists a reliable method for genetically screening organisms for a mutation and keeping that line constant. A new technique using balancer chromosomes is explored in the paper "The Autosomal Flp-Dfs Technique for Generating Germline Mosaics in Drosophila Melanogaster." This paper showed for the first time that you can screen for a recessive mutation that only shows phenotype when homozygous. Using old balancer chromosome methods, genetic screening only allowed you to pick out heterozygous dominate mutations. This experiment uses clonal screening to detect homozygous individuals and kept them in a constant line.

They achieved this by using a gene isolated from yeast. This gene is called FLP recombinase and causes large chromsomal inversions. Through trial and error they found that they could recombine the chromosomes such that each has the recessive mutation while the other half contained half of a balancer chromosome with a physical marker and a lethal recessive. The other homolog did not contain the lethal recessive in the lines that survived. Figure 1 in the paper illustrates the screen. This new technique allowed recessive screening in 95% of the Drosophila genome. It also greatly improved yields in germ line mutations.

Another published paper that employed the use of balancer chromosomes is "Inhibition of RNA Interference and Modulation of Transposable Element Expression by Cell Death in Drosophila." This paper demonstrates the power of balancer chromosomes and what can be accomplished with genetically stable lines. A line was established that exhibited low levels of cell death and was named EGFPir hs-hid. The RNAi levels were analyzed and they found interesting results in the cells undergoing low levels of cell death and the surrounding cells in the tissue. They found that these cells would shut down their RNAi mechanism via maintaining RNA in a double stranded state. If RNA remains in a double stranded state then the RNAi mechanism of gene silencing is shut down.

The authors speculated that this response was an evolutionary trend toward redundant immune response against RNA viruses. If one cell is already undergoing cell death to attempt to stop spread of a virus, then the RNAi immune response has been ineffective. This causes another immune response that attempts to stop the virus which is binding double stranded RNA and keeping double stranded so that it cannot be transcribed into virus proteins. The mechanism of maintaining double stranded RNA is not known.