Two decades ago we learned to “read” the human genome – the entire three-billion-letter DNA recipe for life coiled in the human chromosomes. Now scientists want to start writing it.

A $100 million global consortium has been proposed, to devise ways to assemble human DNA in the laboratory so as to better understand how it works, and look for new ways of treating disease and saving lives.

So far, the scientists in question haven’t the technology, the money, or the public support. But a proposal launched in the journal Science, led by Jef Boeke of the New York University Langone Medical Centre and colleagues, aims explicitly to tell citizens and taxpayers what they hope to do, and why, and encourage public interest and involvement.

The original project to sequence the entire human genome was conceived 30 years ago as a slow, costly, once-only mission: biology’s version of the Apollo moon landings. The full sequence was published in in 2003.

But dramatic advances in robotics, computing and molecular biology now mean that biologists have astonishing amounts of information not just about what DNA spells out for conception, development, reproduction and disease in humans, but in hundreds of microbes, crop plants, laboratory and domestic animals, reptiles and insects. They can sequence DNA, analyse it, and edit it in relatively small lengths. They have been manipulating DNA in the biotechnology industry for 40 years.

But they don’t yet know how to put a lot of DNA together to see how a complex organism works.

The scientists write that they want to be able to do so with public support and within an ethical and legal framework for what would be synthetic human biology. They do not aim to synthesise a human, but to understand how human genes work together in cells in a laboratory dish.

“The major benefit is an enhanced understanding of things like chromosome structure and how the genome works – it is a basic understanding effort in the same way as sequencing the human genome has given us a huge amount of information, and thrown up some surprises,” said Susan Rosser, one of the signatories, and who holds the chair of synthetic biology at Edinburgh University.

“There is no question of humans being made – we are simply talking about cell lines and pieces of DNA.”

Synthetic biology is not new: in 2010 the scientist-entrepreneur Craig Venter who helped accelerate the human genome project announced that his team had after years of effort, synthesised a simple life form. In March 2016 he announced the completion of an organism with what he said were the minimum number of genes necessary to sustain life.

His creation replicated itself in a laboratory dish with just 473 genes. And, he said at the time, what was humbling was that the organism’s own creators had no idea what a third of those genes did.

But humans have more than 20,000 genes. The backers of the new project – dubbed the Human Genome Project–Write (HGP-Write) to distinguish it from the original HGP-Read – propose hugely ambitious and technologically challenging projects such as the construction of a human chromosome, or the making of a human cancer genotype. They want to experiment with the biological machinery of virus resistance or genes, that could suppress tumour formation, and they want to work out how to do it cheaply.

One unexpected aspect of the human genome sequence was that only 2% of the genetic sequence actually codes for genes that make proteins, said Paul Freemont, co-director of the Centre for Synthetic Biology at Imperial College in London. This left 98% of the genome sequence unaccounted for.

“The human genome synthesis project is a natural extension of this project in that by synthesising the human genome we will be able to uncover what the ‘dark matter’ in the human genome does and why we have it,” he said.

But his colleague Tom Ellis was not so sure. “I should say that for synthesising the complete human genome I am still on the fence. I am not particularly sold on it yet. While we will probably learn a lot from it and it will drive the technologies, I don’t see an obvious use for it at the end when we are done.”

But he would prefer to see it done by a team of academics rather than individuals who might claim patents.

“The idea of discussing it and coming to some sort of ethical and technological standards before anyone starts work on this, I really like the idea of.”