X-rays can cause reverse mutation in D. melanogaster

Dr. Mel Green is a professor Emeritus of Molecular and Cellular Biology here at UCDavis. He was garnered many prestigious findings throughout his long career in genetics and has worked at many top universities and worked with many others who have been integral in discovering more about genetics. Dr. Green came to our MCB 164 class and gave a spectacular guest lecture, the best part of which was when he told us to put down our pencils. He described to us how he came to work with Drosophila and how he discovered many of the things he did including the discovery of mobile DNA elements. I was curious to see how exactly Dr. Green was involved in finding out that x-ray's could produce reverse mutations and i found this article where he and a colleague here at Davis figured it out using the vinegar flies.


In this experiment, Green was discussing how different experimenters found contradicting evidence that this could be done. He questioned the current techniques many people were using for reverting mutations and his main goal was to definitively prove that x-ray's can in fact induce reverse mutations. Some also found that the rate of reverse mutation was lower than that of direct mutation. Based on the other experiments Green could also see that different alleles and species had different rates of reverse mutation. He postulated that the differing results stemmed from the theory that perhaps some forks were irreversible while others were, which gave rise to opposing papers. Specifically, he wanted to test in this experiment whether or not out of the 4 variable forked alleles, whether or not each allele would allow a reverse mutation or not.
He exposed the males and females to 5000 rads and 4000 rads, respectively. He then mated each sex to an opposite sex that has not been irradiated. he screen for various phenotypes including bristle type, eye color, and body color to see if revertants were produced.
His experiments yielded surprising results, he found that none of the male sperm alleles gave rise to reverse mutations, but one specific allele (f3n) for homozygous females clearly showed a high frequency of reverse mutations.

In his discussion he acknowledges that male sperm are haploid and the female flies were diploid which may have something to do with the results, but he also noted that during spermatogenesis there is NO crossing over while in oogenesis there is. Which led to another question: Does reversibility of mutations have to do with crossing over ability?I just found it quite interesting that x-rays can return a mutant allele to completely wild-type, leading to a production of completely normal looking female flies.


Lefevre, G, Jr., Green, M. M., 1958, Reverse mutation studies on the forked locus in Drosophila Melanogaster, Genetics, v. 44, p. 769.