In an effort to preserve rare varieties of chicken breeds and diversify the chicken gene pool, scientists at the University of Edinburgh's Roslin Institute have come up with a plan to breed genetically-modified chickens designed to act as surrogates that would be capable of laying eggs from any rare breed. Such rare breeds include the Nankin, Scots Dumpy and Sicilian Buttercup. The Guardian reports: The surrogacy technique, which places a new, mind-bending twist on the classic chicken or egg question, involves first genetically engineering hens to be sterile. This is done by deleting a gene, called DDX4, that is required for the development of primordial follicles (the precursors to eggs) meaning that the surrogate hens will never lay eggs that are biologically their own. The next step will be to transplant follicles from rare birds into the surrogate (this is done before the surrogate chick is hatched from its own egg), meaning it would go on to lay eggs belonging to entirely different breeds of chicken. Given that the hens would also need to be artificially inseminated with sperm from the same rare variety, the approach may appear unnecessarily convoluted. Why not just breed the rare birds the normal way? The scientists' ultimate goal is to create a gene bank of chicken breeds preserved for posterity, and since primordial follicles can be frozen efficiently, while eggs cannot, the surrogacy technique serves an essential work-around. Mike McGrew, who is leading the project and is the first author on a paper on the work published this week in the journal Development, predicts that the surrogates will be able to lay eggs from any breed, including chicken's wild predecessor, the red junglefowl, but he is doubtful about whether it will work efficiently across species -- it is not likely that the surrogate hens will be giving birth to eagle chicks, for instance. Richard Broad, a field officer for the Rare Breeds Survival Trust, agreed that rare chickens could be a source of valuable genetic variation, potentially carrying variants that would provide resistance against new forms of avian flu. At present, the team is focused on chicken breeds, but expects the technique to work to preserve rare varieties of ducks, geese and quail.