Gender-bender chicks are hot stuff

Agricultural policy, smart salmon and sex-change chickens at the British Association's annual festival of science in Leeds

Chickens and crocodiles have more in common than previously thought, say researchers from Manchester University who have bred "gender-bender" chickens.

Mark Ferguson of Manchester University's school of biological sciences believes the sex of some chicks can be influenced by temperature as well as by chromosomes. If his research works on a large scale, it could benefit the poultry industry financially, while saving the lives of thousands of chickens each year, he says.

The research is based on findings from the 1980s that showed alligators and crocodiles, like many reptiles, had no sex chromosomes, relying instead on temperature for sex determination. Incubation of eggs at between 28oC and 31oC produced all females, incubation at 32oC produced 50 per cent males and females, while incubation at 33oC produced all males. The researchers were interested in how this temperature sex determination worked and whether it could be replicated in other egg-laying animals.

"We think from our work that it is very similar to chromosome sex determination," said Professor Ferguson. "We think the basic sex is female. Something has to happen to shift you from being female to male. In mammals, males get the extra gene in the y chromosome, while in crocodiles everyone gets the same genes, but the effects of the gene are a function of temperature. We believe it is that dose which makes something go from female to male."

The researchers turned their attentions to chickens, where almost 50 per cent are wasted, as only females of some varieties are wanted for eggs and males of others for meat. They found that if they exposed chickens, whose sex determination is largely chromosomal, to short pulses of temperature they could change the sex of a small percentage of chicks.

"We call these gender bender chickens," said Professor Ferguson. "There will be a small percentage of animals that get just enough of the gene dose on the chromosome to make them male, while some will just fail to get enough of the dose and are female. We believe temperature and chromosome interact additively to give the final dose."

Breeding from female gender-bender chickens, which have two * chromosomes despite being female, can ensure all male offspring, says Professor Ferguson.