Could our Friday night fish and chips also be a missing piece to the puzzle of human DNA?

The unusual looking elephant shark (Callorhinchus milii), commonly used in fish and chip shops throughout New Zealand, is only a very distant relative of humans.

But, in a new study, University of Otago geneticists have discovered it has a remarkably similar DNA memory system to our own.

"This memory is made up of tiny chemical tags called methylation, which are used to tell a cell what its job is and make sure it stays dedicated to it," said research leader Dr Tim Hore, of the university's Department of Anatomy.

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The DNA memory system that belongs to humans has only been found in vertebrates - animals with a backbone such as mammals, amphibians and fish - and researchers have long wondered how it evolved and how far back in evolutionary time it exists.

First author of the study, Dr Julian Peat, said the fact elephant sharks also use methylation-tagging to turn off genes tells us this memory system has been around a long time.

Our ancestors split off from elephant sharks more than 460 million years ago.

"Our study identifies elephant shark as the most evolutionarily distant animal that shares this DNA-regulation system with us humans, which makes it very interesting to take a closer look at," Peat said.

Hore said that, with access to this unique genetic resource, the team was excited about further research on the elephant shark and its DNA.

"The elephant shark is something of a living fossil - it's the slowest evolving vertebrate we know of. It only lives in the cooler waters of Australia and New Zealand, so we are really fortunate to have something this valuable to science in our backyard.

"So many things remain mysterious about the elephant shark - we don't know whether this methylation memory persists across generations, or if it contributes to how gender is decided."