Masly knew that chromosome #4 on melanogaster held a gene that was somehow very important for fertility--information found earlier by Rochester biologist H. Allen Orr. Crossbreeding the flies proved tricky because a few million years of evolution separated the species, but after a few nudges the flies produced what Masly was looking for--a sterile male.
This is when Dobzhansky's 70-year-old hypothesis nearly died for good.
The reigning theory of speciation says that the genes causing hybrid sterility must have diverged slowly by normal evolutionary changes. To determine whether this was true, Masly had only to look at chromosome #4 and find the gene on it that caused the hybrid sterility.
But there was no gene there.
"There was a great, 'Oh no,' moment," says Masly. "I'd been working on this for six years and it was starting to look like it was all for nothing. Something was all wrong. We couldn't find the gene and we were this close to giving up on the whole project."
But once again, insights from the past came into play. Masly and Orr, Masly's advisor and professor of biology at the University of Rochester, were talking one day when Orr suddenly recalled an off-hand comment from a scientist named Hermann J. Muller in a paper 60 years earlier. Muller speculated that perhaps since the sterility in the flies is so recessive--meaning it's almost completely non-functional--perhaps the gene in question has jumped clear off the chromosome.
"It had never occurred to us that the gene might have moved right off chromosome #4 in simulan
Source:University of Rochester