Decoded: How honeybees determine sex

The truth behind the unique sex-determination system in honeybees - where males develop from unfertilised eggs and females develop from fertilised eggs - is out.

Five amino acid separate males from females in honeybee colonies, say scientists who added that the molecular switch for haplodiploidy - genetic sex-determination - was gradual and adaptively evolved in honeybees.

Robert E. Page, study's co-author and provost of Arizona State University, and Martin Beye, lead author and professor with Institute of Evolutionary Genetics in the University of Dusseldorf, Germany, studied 14 natural sequence variants of the complementary sex determining switch (CSD gene) for 76 genotypes of honey bees.

What the authors found was that at least five amino acid differences can control allelic differences to create femaleness through the CSD gene - the control switch.

The scientists also found that honey bees' high recombination rate - the process by which genetic material is physically mixed during sexual reproduction - is the highest of any known animal studied.

This helped the researchers isolate, sequence and characterise the complementary sex determining locus, said the study published in the journal Current Biology.

"We discovered that different amounts of arginine, serine and proline affect protein binding sites on the CSD gene, which, in turn, lead to different conformational states, prompting functional changes in the bees - the switch that determines the shift from female to not female," said Page.

The system of haplodiploid sex determination, ultimately evolved at a molecular level, has remained one of the most important questions in developmental genetics.

Haplodiploidy is where males develop from unfertilised eggs and are haploid (have half the number of chromosomes than a female has), and females develop from fertilised eggs and are diploid (have 32 chromosomes).

In this system, typical of bees and wasps, sex is determined by the number of sets of chromosomes an individual receives.