The scientists think that the proteins made by the two different versions of csd in a female pair up to form a single unit which acts on the next step in sex determination, probably by affecting the expression of other genes. If only one type of csd is made, no active protein is formed and the bee grows into a male.

"The csd gene is the major invention that enabled the evolution of the ants, bees and wasps and their complex societies by enabling the evolution of haplodiploidy," Page said. Because males have just one set of genes, sisters that work together in the nest share more genes in common with each other than they would with their own sons and daughters.

But this also has a downside for bee breeders. When bees are inbred to select desired traits, fertilized eggs with two copies of the same csd allele can occur. These eggs develop into sterile diploid males. Worker bees find and kill these sterile males as larvae. That means that inbred honeybee colonies quickly die out.

"This problem has haunted bee breeding since the 1940s. As we understand more, there will be ways to get around this problem," Page said. Beekeepers could set up matings with bees of different csd type, or find ways to manipulate the gene to get viable crosses.

Breeding bees is hard enough already. Wild bees mate only once, in flight to their new nest. In the 19th century, Gregor Mendel, who discovered the principles of inheritance in pea plants, also tried to breed bees without success. In the 1940s, Harry H. Laidlaw, Jr. now a professor emeritus of entomology at UC Davis, and others pioneered methods for artificial insemination of bees, allowing selective breeding for the firs
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Contact: Andy Fell
ahfell@ucdavis.edu
530-752-4533
University of California - Davis
21-Aug-2003