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categories: ["genetics"]categories: ["genetics"]tags: ["synthetic biology", "dna synthesis", "genome engineering", "minimal cell", "biosecurity"]tags: ["synthetic biology", "dna synthesis", "genome engineering", "minimal cell", "biosecurity"]summary: "Genomes designed on a computer and assembled from chemically synthesized DNA, then installed in a cell to see whether the design lives."summary: "Genomes designed on a computer and assembled from chemically synthesized DNA, then installed in a cell to see whether the design lives."updated: "2026-07-27"updated: "2026-10-29"humanEvidence: "Nothing has been done in a person. The built genomes are bacterial and yeast, human-directed work is confined to cultured cells, and no synthetic human chromosome exists as of 2026."humanEvidence: "Nothing has been done in a person. The built genomes are bacterial and yeast, human-directed work is confined to cultured cells, and no synthetic human chromosome exists as of 2026."access: "Nothing to obtain as a product: genome-scale writing is done by a small number of funded laboratories, while commercial suppliers sell only short DNA fragments, subject to order screening."access: "Nothing to obtain as a product: genome-scale writing is done by a small number of funded laboratories, while commercial suppliers sell only short DNA fragments, subject to order screening."reversibility: "irreversible"reversibility: "irreversible"lines 30–36 → 30–3615 unchanged lines not shown
}}`````` **Synthetic genomes** are chromosomes designed as text and then built as molecules: an organism's genetic instructions written in a design file, assembled from short synthetic DNA fragments, and installed in a cell to see whether it functions. The point is not to copy nature but to test it. A designed genome states exactly which genes an experimenter believes are necessary and which changes are tolerable, and the cell either grows or it does not. That makes genome writing a comprehension test as much as an engineering achievement — the claim of the field's founders being that what cannot be built is not understood.**Synthetic genomes** are chromosomes designed as text and then built as molecules: an organism's genetic instructions written in a design file, assembled from short synthetic DNA fragments, and installed in a cell to see whether it functions. The aim is to test nature rather than to copy it. A designed genome states exactly which genes an experimenter believes are necessary and which changes are tolerable, and the cell either grows or it does not. That makes genome writing a comprehension test as much as an engineering achievement; the field's founders argue that what cannot be built is not understood. ```figure```figure{"key": "dna-double-helix", "caption": "Writing a genome means assembling this molecule to a specification, rather than copying one that already exists."}{"key": "dna-double-helix", "caption": "Writing a genome means assembling this molecule to a specification, rather than copying one that already exists."}lines 47–53 → 47–5310 unchanged lines not shown
## Development history## Development history The field has advanced by roughly one order of magnitude of genome size per decade, and each step has been limited by assembly and installation rather than by the chemistry of making DNA. The sequence below is also a sequence of increasing ambition: from copying a viral genome, to copying a bacterial one, to redesigning a eukaryotic one.The field has advanced by roughly one order of magnitude of genome size per decade, and each step has been limited by assembly and installation rather than by the chemistry of making DNA. Ambition rose with each step: from copying a viral genome, to copying a bacterial one, to redesigning a eukaryotic one. ```timeline```timeline[[lines 56–62 → 56–622 unchanged lines not shown
{ "year": "2010", "title": "JCVI-syn1.0", "text": "A synthesized Mycoplasma mycoides genome is transplanted into a recipient cell, which then replicates under the control of the built chromosome." }, { "year": "2010", "title": "JCVI-syn1.0", "text": "A synthesized Mycoplasma mycoides genome is transplanted into a recipient cell, which then replicates under the control of the built chromosome." }, { "year": "2014", "title": "First synthetic eukaryotic chromosome", "text": "The Sc2.0 consortium reports a redesigned, functional yeast chromosome III, stripped of transposons and introns." }, { "year": "2014", "title": "First synthetic eukaryotic chromosome", "text": "The Sc2.0 consortium reports a redesigned, functional yeast chromosome III, stripped of transposons and introns." }, { "year": "2016", "title": "Minimal cell", "text": "JCVI-syn3.0 is reduced to 473 genes, of which a substantial fraction have no known function." }, { "year": "2016", "title": "Minimal cell", "text": "JCVI-syn3.0 is reduced to 473 genes, of which a substantial fraction have no known function." }, { "year": "2019–2021", "title": "Recoded Escherichia coli", "text": "A 4-megabase E. coli genome is rebuilt with three codons removed, and the corresponding transfer RNAs and release factor deleted." }, { "year": "2019-2021", "title": "Recoded Escherichia coli", "text": "A 4-megabase E. coli genome is rebuilt with three codons removed, and the corresponding transfer RNAs and release factor deleted." }, { "year": "2023", "title": "Sc2.0 chromosomes completed", "text": "All sixteen synthetic yeast chromosomes are reported, along with a designed neochromosome carrying relocated transfer RNA genes." }, { "year": "2023", "title": "Sc2.0 chromosomes completed", "text": "All sixteen synthetic yeast chromosomes are reported, along with a designed neochromosome carrying relocated transfer RNA genes." }, { "year": "2025", "title": "Human chromosome project announced", "text": "A UK-funded programme is announced to develop the tools for building a synthetic human chromosome in cultured cells, with an attached social science strand." } { "year": "2025", "title": "Human chromosome project announced", "text": "A UK-funded programme is announced to develop the tools for building a synthetic human chromosome in cultured cells, with an attached social science strand." }]]lines 64–72 → 64–721 unchanged line not shown
## Minimal cells## Minimal cells The most informative result to come out of genome writing is negative. In building a stripped-down *Mycoplasma*, the Venter Institute found that a genome could be cut to 473 genes and still sustain a free-living cell — but that roughly a third of those genes had no assigned function.[^hutchison2016] They were necessary and unexplained. A decade of sequencing and annotation had not identified them, and only the requirement to build a working cell exposed the gap.The most informative result to come out of genome writing is negative. In building a stripped-down *Mycoplasma*, the Venter Institute found that a genome could be cut to 473 genes and still sustain a free-living cell, but that roughly a third of those genes had no assigned function.[^hutchison2016] They were necessary and unexplained. A decade of sequencing and annotation had not identified them, and only the requirement to build a working cell exposed the gap. Later versions restored a small number of genes to fix abnormal cell division, producing a strain that grows and divides more normally and that now serves as a chassis for studying how a minimal set of parts organises a cell. The lesson generalises: gene-by-gene knockout studies systematically miss redundancy, and only a whole-genome design forces the question of sufficiency.Later versions restored a small number of genes to fix abnormal cell division, producing a strain that grows and divides more normally and that is now used as a chassis for studying how a minimal set of parts organises a cell. The lesson generalises: gene-by-gene knockout studies systematically miss redundancy, and only a whole-genome design forces the question of sufficiency. ## Sc2.0 and the rewritable genome## Sc2.0 and the rewritable genome lines 76–86 → 76–863 unchanged lines not shown
## Recoding and virus resistance## Recoding and virus resistance Rebuilding a genome allows changes no editing tool could make efficiently, because they must be applied at thousands of positions at once. Removing every instance of a codon from a bacterial genome, then deleting the machinery that reads it, frees that codon for reassignment to a non-standard amino acid — and incidentally renders the cell unreadable to viruses, whose genomes still use the original code. These consequences are treated in detail in [[recoded-organisms]].Rebuilding a genome allows changes no editing tool could make efficiently, because they must be applied at thousands of positions at once. Removing every instance of a codon from a bacterial genome, then deleting the machinery that reads it, frees that codon for reassignment to a non-standard amino acid, and incidentally renders the cell unreadable to viruses, whose genomes still use the original code. These consequences are treated in detail in [[recoded-organisms]]. ## Human genome writing## Human genome writing Genome Project–write, proposed in 2016 by a group including Jef Boeke and [[george-church]] as a successor to the Human Genome Project, aimed to reduce the cost of designing and building large genomes by orders of magnitude.[^boeke2016] Its announcement was clumsy: an invitation-only meeting closed to press prompted public criticism from synthetic biologists and bioethicists that a project of this kind should not begin behind a closed door, and the organisers subsequently reframed the goal around cells rather than organisms. The flagship proposal became an "ultra-safe" human cell line, recoded for resistance to viral infection, which would be valuable for biomanufacturing and would sidestep the question of synthetic people entirely. The same reasoning drives the multiply edited donor animals used in [[xenotransplantation]], where inactivating endogenous retroviruses is a prerequisite rather than a bonus.Genome Project-write, proposed in 2016 by a group including Jef Boeke and [[george-church]] as a successor to the Human Genome Project, aimed to reduce the cost of designing and building large genomes by orders of magnitude.[^boeke2016] Its announcement was clumsy: an invitation-only meeting closed to press prompted public criticism from synthetic biologists and bioethicists that a project of this kind should not begin behind a closed door, and the organisers subsequently reframed the goal around cells rather than organisms. The flagship proposal became an "ultra-safe" human cell line, recoded for resistance to viral infection, which would be valuable for biomanufacturing and would sidestep the question of synthetic people entirely. The same reasoning drives the multiply edited donor animals used in [[xenotransplantation]], where inactivating endogenous retroviruses is a prerequisite rather than a bonus. In 2025 a British funder committed to a programme aimed at developing the tools to build a synthetic human chromosome, with an explicit remit confined to cells in culture and a parallel social science strand. As of 2026 no synthetic human chromosome exists. The gap is quantitative and large: a human genome is close to a thousand times the size of the largest genome yet assembled from synthetic DNA, mammalian cells have no equivalent of yeast's chromosome-replacement machinery, and chromatin structure, imprinting and long-range regulation are design variables nobody knows how to specify.In 2025 a British funder committed to a programme aimed at developing the tools to build a synthetic human chromosome, with an explicit remit confined to cells in culture and a parallel social science strand. As of 2026 no synthetic human chromosome exists. The gap is quantitative and large: a human genome is close to a thousand times the size of the largest genome yet assembled from synthetic DNA, mammalian cells have no equivalent of yeast's chromosome-replacement machinery, and chromatin structure, imprinting and long-range regulation are design variables nobody knows how to specify. lines 95–101 → 95–1018 unchanged lines not shown
## Outlook## Outlook The near-term work is unglamorous: cheaper and more accurate synthesis, enzymatic rather than phosphoramidite chemistry, better assembly in mammalian cells, and design rules that predict whether a rewritten sequence will function before it is built. The deeper question is what genome writing is for. In bacteria and yeast the answers are concrete — chassis organisms, virus resistance, non-standard chemistry. For human cells the strongest case is a virus-resistant manufacturing line, which is a narrow industrial goal supporting a very broad capability, and the field has not settled whether that asymmetry is acceptable.The near-term work is unglamorous: cheaper and more accurate synthesis, enzymatic rather than phosphoramidite chemistry, better assembly in mammalian cells, and design rules that predict whether a rewritten sequence will function before it is built. The deeper question is what genome writing is for. In bacteria and yeast the answers are concrete: chassis organisms, virus resistance, non-standard chemistry. For human cells the strongest case is a virus-resistant manufacturing line, which is a narrow industrial goal supporting a very broad capability, and the field has not settled whether that asymmetry is acceptable. ## See also## See also removed, struck through added, underlinedLine numbers count the serialised markdown of each revision, frontmatter included.
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