The gene, named `p phi 2', is present on `x' sex chromosome in both sexes but is expressed only in males, Dr Lalji Singh, director of Hyderabad-based centre for DNA fingerprinting and diagnostics (CDFD), said at the seventh international congress of reproductive immunology here.

So far, scientists abroad have identified four genes that have a role in the complex pathway of determining whether an undifferentiated embryo will ultimately develop into a male or female.

These include `sry' which is involved in formation of testes and `zfy' which has been shown to be involved in sperm formation.

Two more, `sox 9' and `sox 3', have been classified under the `sry' group.

The CDFD scientists came across their new gene while working on the genetic material of snakes that are considered a unique material for studying the evolution and function of sex chromosomes.

The new gene wassubsequently isolated from mouse and human genetic material too. Their finding was reported in the British medical journal The Lancet.

Dr Singh reported his team has also found a unique case of a person who had physical characteristics of a female but all normally functioning male sex genes.

This case had 47 chromosomes instead of the normal set of 46. There were two `x' and one `y' chromosomes unlike normal females who had two `x' and males who had one `x' and one `y' chromosome.

A person with two `x' and one `y' chromosome would normally be expected to be sterile male, but the unique case turned out to be a female.

CDFD scientists also found to their surprise that the other male sex genes such `sry', `zfy' and `sox 9' were functioning normally in this case.

This indicates presence of many more unidentified genes involved in sex determination, Dr Singh said.