London, March 19 (IANS): Scientists have revealed, for the first time, the mystery behind why chromosome errors are high in women's eggs.

It is estimated that up to 60 percent of eggs are affected by errors in how their chromosomes divide - making it the leading cause of infertility - a study has said.

Chromosome errors also lead to conditions such as Down Syndrome and early pregnancy loss, researchers from University of Southampton added.

By using state-of-the-art imaging techniques, the researchers examined the most important process present in all cells to prevent chromosome errors - the Spindle Assembly Checkpoint (SAC).

They looked at how it behaves in oocytes, developing female sex cells.

The SAC acts as a gatekeeper, only allowing a cell to pass through - and so divide - if its chromosomes are all ready to do so - in order to preserve the cell's identity and proper function.

If cells do not have a SAC, or the SAC is damaged in some way when cells divide, often the female cells inherit the wrong number of chromosomes.

“We found that in oocytes, the classical model of how this gatekeeper works, from a closed gate to open gate, does not operate. Instead, the gate is continually left ajar,” noted researchers Simon Lane and professor Keith Jones from university's centre for biological sciences.

“As such, an oocyte can divide its chromosomes and becomes aneuploid - a cell with fewer or more chromosomes than usual - quite easily, because the SAC is not preventing the division,” Lane explained.

The findings gives us a better understanding for what is controlling chromosome division in eggs.

“Armed with such knowledge, we could potentially find ways of improving this control mechanism or alternatively find ways of screening eggs as they are dividing to detect a good egg from a bad egg,” Jones added.

Although this screening would obviously only benefit people in an IVF setting where eggs are recovered from the patient, she contended.