"We normally feed our fruit flies yeast, and that stimulates egg development," said Bickel. "However, in these experiments, we gave them yeast for a day, to allow their eggs to mature, but then we took them off the yeast and put them on sugar for four days. Although they had a food source that kept them healthy, egg-laying was inhibited and this caused the eggs to "age" within the body of the female."
To assess whether errors occurred during the meiotic cell divisions of the egg, the researchers used genetic markers that affect the fly's body color and shape of the eye.
"After the egg is fertilized and grows into an adult, we can use these markers to tell whether or not meiotic nondisjunction happened in the egg," said Bickel. "With the strain of flies that we used, we saw a dramatic increase in nondisjunction of aged versus non-aged eggs."
Bickel explained that, in humans, there may be a back-up system that functions in young eggs to prevent these meiotic mistakes. However, one theory is that in older eggs, some component of the system has deteriorated with time and no longer works properly.
"This is a very initial finding," says Bickel. "We've simply discovered that fruit flies, under these conditions, can mimic what happens in humans. There's a whole set of experiments we can do now to start to find out what exactly is going wrong. It really opens up the field."
The other authors on the paper are Charlotte A. Jeffreys, laboratory technician in the department of Biological Sciences, and Peter S. Burrage, a 2000 Dartmouth graduate who is now an MD/Ph.D. student at Dartmouth. This study was initiated with funds from the Hitchcock Foundation and continued with grants from the March of Dimes and the National Institutes of Health.