When closely related individuals mate, their offspring are likely to end up with identical alleles for many traits. Many potentially harmful recessive alleles are no longer masked by dominant alleles, so more genetic disorders arise. Similarly, offspring that inherit two identical alleles for some traits will also lose any advantages once conferred by overdominance.
Biologists have long wondered which of these mechanisms causes the reproductive failures seen in inbred populations. "It's still being debated," Paige said.
The new study found that about 75 percent of the reproductive declines seen in the inbred flies could be attributed to the loss of dominant alleles and the subsequent "unmasking" of deleterious alleles. More surprisingly, the data also indicated that 25 percent of the declines were due to the loss of overdominance.
"That means we have two mechanisms ongoing," Paige said. "One does predominate, but the other may be important, too."
The fact that a relatively large number of genes are affected by inbreeding is bad news for conservationists hoping to save small populations of plants or animals from extinction, Paige said.
It means that there is no easy fix to the problem of inbred populations. The best approach is to try to preserve and maintain genetic diversity in natural populations well before they begin their slide into an "extinction vortex," he said.
|Contact: Diana Yates, Life Sciences Editor|
University of Illinois at Urbana-Champaign