About a month ago, I made a double homozygous mutant, expecting to see a genetic interaction between two genes. I got a very severe morphological phenotypes which included severely dpy worms, some molting defects, bursting vulva and (practically) sterile animals, although not completely sterile, at a very high penetrance in the F3s.
I had enough worms from the F3 to genotype them by PCR and they were double homozygous. I kept the plate, hoping that they could produce enough worms to maintain the strain. However, over the next two or three generations, there started to appear some essentially wild type worms, albeit with severe dpys still appearing on the plate. The penetrance of the defect is not as high as it was originally.
Is this a common occurence?? I have read a fair bit of C.elegans literature but never have come across this before. I just think that there is a possibility for selective pressure to produce a background mutation naturallythat suppresses the double mutant.
I want to go back and remake the double mutant, this time with a balancer and have it throw out the double homozygous from which I will then study. My question is whether others think this is valid, or should I be working with the strain (with lower penetrance of defect) that I have above.
Any suggestions, comments or similar examples would be appreciated.