IT is a question worthy of the scientists of 'CSI Miami' -- which has the more complex gene structure a human being or the humble flea?
The answer may be surprising but, in terms of genetic complexity the humble water flea beats humans hands down.
Scientists have learnt that the one millimetre-long creature has more genes than any other animal known.
In total, around 31,000 genes are packed into its DNA. In comparison, humans have only around 23,000.
The common water flea, 'Daphnia pulex', is the first crustacean to have a blueprint made showing the sequence of chemicals that make up genetic code, or genome.
At first glance, Daphnia seems ordinary enough, having a transparent body, jointed limbs, compound eyes and a simple nervous and circulatory system.
"More than one-third of Daphnia's genes are undocumented in any other organism -- in other words, they are completely new to science," said Dr Don Gilbert, one of the researchers from Indiana University in the United States.
The animal has unique ways of responding to stress, with some species producing exaggerated tail spines, neck teeth or protective helmets when threatened by predators.
Daphnia can also adapt to wide ranges in acidity, toxins, oxygen concentrations, food quality and temperature.
The creatures are able to reproduce both sexually and asexually and they thrive in the absence of males by clonal reproduction until environmental conditions favour sex.
A high rate of gene duplication is the main reason why Daphnia has so many genes, say the researchers. The scientists hope that sequencing the Daphnia genome will lead to a better understanding of how organisms respond to environmental changes.