Delivering a special lecture on `Sex determination' here today, Prof Mark W J Ferguson of the University of Manchester said studies have shown that all alligator eggs that went through a temperature ambience of 29 to 31.5C hatched into females. But if the temperature was slightly raised to 32.5c, all the hatchlings turned out to be males. If the temperature was further raised to 35C, the embryos switched back to produce truly `hot' females.

It is this temperature mechanism that has led to a larger female population among alligators. The female alligator is highlysex-biased and builds nests where the temperature is in the 29-30 threshold range. This has resulted in a 6:1 female to male population ratio among alligators and one reason why the species did not go extinct or through a population bottleneck.

The mystery behind the sex change due to temperature variation has not been fully understood. While one school of thought believes that genes may really not have a role to play in sex determination in alligators, the other doubts the hsp-90 protein in the switch-over drama. However, what is now known is that there is a definite window period when heat can change the sex profile.

Research in this field has a big commercial implication, according to Prof Ferguson. In chicken, companies can either go in for broilers for meat or eggs, depending on market needs.

But the catch came at the end of Prof Ferguson's talk when scientists wanted to know if the sex change is applicable to human beings too. The British researcher dismissed it with a dash of humour saying thatit is not possible to stuff people into refrigerators or toss them into an oven for a child of choice. But Prof Lalji Singh, Director of the Centre of Cellular and Molecular Biology (CCMB), wondered what would happen if human embryos are taken out early and warmed up a bit or cooled down. What would the sex determining genes then say? The talk was held by the British Council as part of `Bright Sparks', a festival showcasing science in UK.