The Genomic Equivalence Principle
A neuron never divides again after birth. Yet it carries the same instructions for making muscle, skin, and bone as a myoblast or keratinocyte does. How can a single fertilized egg give rise to over 200 visibly distinct cell types? These include a red blood cell with no nucleus, a neuron a meter long, and a liver cell packed with metabolic enzymes. This is puzzling if every one of them, in principle, started with an identical genome. The question sits at the foundation of developmental biology. The answer determines whether development is a process of progressive genetic loss. In this view, cells throw away DNA they no longer need. Or it is a process of selective genetic use. In this view, cells keep the whole library but read only certain volumes. The genomic equivalence principle states something important. The overwhelming majority of somatic cells retain a complete, unabridged copy of the genome. This is the same genome present in the fertilized egg. Differentiation is the process by which cells become structurally and functionally specialized. It is not achieved by deleting genes. Instead, it works by regulating which genes are transcribed, when, and how much. This is one of the most consequential ideas in all of biology. It means every somatic cell nucleus is, in principle, capable of directing development of an entire new organism. This is because it holds the entire genetic blueprint. This principle matters far beyond an interesting fact about DNA content. It resolves an old conceptual puzzle. How can differentiated states stay so stable across many mitotic divisions, if nothing is physically lost? The answer locates the memory of cell identity not in the DNA sequence itself. Instead, it lies in the pattern of gene expression layered on top of it. This includes transcription factor networks, chromatin marks, and DNA methylation. This principle also opens the experimental door to nuclear transfer, reprogramming, and cloning. If the genome is intact, a differentiated nucleus can in principle be reset to totipotency. This fact was later exploited to clone Dolly the sheep. It also enabled the conversion of adult cells into induced pluripotent stem cells. This article traces the logic and evidence behind genomic equivalence. It covers the classic nuclear transplantation experiments that established it. It examines the important exceptions that prove the rule. It explains the molecular mechanism of differential gene expression. This mechanism explains how identical genomes produce different phenotypes. Finally, it covers modern technologies that genomic equivalence made conceivable. These include cloning, iPSCs, and epigenetic reprogramming.
- Nearly all somatic cells contain the same complete genome as the zygote; differentiation reflects differential gene expression, not gene loss.
- Briggs and King (1952), then Gurdon (1962), proved this by transplanting somatic nuclei into enucleated frog eggs and obtaining normal, sometimes fertile, tadpoles and frogs.
- Gurdon's serial nuclear transplants using fully differentiated intestinal epithelial nuclei showed genomic content is retained even after many mitotic divisions.
- Key exceptions exist: mature red blood cells (mammals) lose their nucleus entirely, lymphocytes rearrange antigen-receptor genes irreversibly, and some organisms undergo programmed DNA loss (chromatin diminution).
- Cell identity is maintained across divisions by heritable regulatory states — transcription factor circuits and epigenetic marks (DNA methylation, histone modifications) — not by changes to DNA sequence.
- Genomic equivalence is the conceptual foundation for reproductive and therapeutic cloning, and for induced pluripotent stem cell (iPSC) technology.
Every somatic cell nucleus (with rare, well-defined exceptions) carries the entire genome of the zygote; cells differ not because they carry different genes, but because they express different subsets of the same genes.
The core idea
Genomic equivalence is the principle that development does not proceed by parceling out different portions of the genome to different cell lineages. Early in the twentieth century this was a genuinely open question. August Weismann had proposed in the 1890s that differentiation might occur through unequal nuclear division, with hereditary "determinants" segregating unequally into different cell lineages so that a muscle cell nucleus would retain only muscle-making instructions and a nerve cell nucleus only nerve-making instructions. This idea was plausible, testable, and — as it turned out — largely wrong for most cells. The alternative view, associated with Theodor Boveri and later championed by Thomas Hunt Morgan, held that all nuclei arising from the zygote by mitosis are genetically identical, and cell diversity arises entirely from differences in cytoplasmic environment acting on an unchanging genome. The resolution came from totipotency and nuclear equivalence experiments: if you can extract the nucleus from a differentiated cell and place it into an environment (an enucleated egg) that strips away its acquired regulatory state, and that nucleus can then direct the development of a complete, normal organism, this proves the nucleus retained the full genetic information necessary for every cell type — it merely was not using all of it in its original context. The technical vocabulary that follows from this: a totipotent cell can give rise to all cell types of the organism including extra-embryonic tissues; a pluripotent cell can give rise to all three germ layers but not extra-embryonic tissues; a multipotent cell is restricted to a related family of cell types (e.g., blood stem cells). Differentiation is the progressive, usually stable, restriction of which genes a cell's transcriptional machinery has access to — not a reduction in which genes physically exist in its nucleus. It's important to be precise about what genomic equivalence does and does not claim. It does not claim every cell nucleus in every organism is perfectly, universally unchanged — there are well-documented exceptions (discussed below) where DNA content really is altered or lost during development. What it claims is that this is the exception rather than the rule, and that the default developmental strategy across nearly all animals and plants is genome retention plus differential gene regulation. This distinction between changing the genome and changing how the genome is read is the single most important conceptual pivot in understanding differentiation, and it connects directly to Differential Gene Expression and Cell Determination and Differentiation.
Mechanism
Step 1 — The zygote's genome is the reference state. The fertilized egg contains two complete haploid genomes (maternal and paternal) that fuse to form a diploid genome. Every somatic cell produced by subsequent mitotic divisions is, by the basic mechanics of DNA replication and mitosis, expected to receive an identical copy of this genome, replicated with high fidelity (error rate roughly 10⁻⁹ to 10⁻¹⁰ per base pair per division, thanks to DNA polymerase proofreading and mismatch repair). The default expectation from mitosis alone is genomic identity across all descendant cells.
Step 2 — Differentiation layers regulatory information on top of the genome, not changes within it. As a cell lineage becomes progressively determined and then differentiated, master transcription factors activate lineage-specific gene batteries while repressing genes for alternative fates. For example, the transcription factor MyoD activates the muscle-differentiation program, while different combinations of transcription factors (Pax6 in eye tissue, Nkx2.5 in cardiac tissue) activate other programs. These factors bind specific DNA regulatory sequences (enhancers, promoters) and recruit chromatin-modifying complexes.
Step 3 — Chromatin structure is remodeled to lock in expression states. Genes not needed in a given cell type are packaged into transcriptionally silent heterochromatin via mechanisms including:
- DNA methylation (addition of methyl groups to cytosines in CpG dinucleotides, typically silencing associated promoters)
- Histone modifications (e.g., H3K27me3 deposited by Polycomb repressive complexes marks repressed developmental genes; H3K9me3 marks constitutive heterochromatin)
- Higher-order chromatin compaction that physically limits access of RNA polymerase and transcription factors to DNA
Crucially, these are epigenetic marks — heritable through mitosis but, in principle, reversible, and not changes to the DNA base sequence itself. This is what makes them different from mutation or gene loss.
Step 4 — These regulatory states are self-perpetuating across cell division. When a cell divides, DNA methylation patterns are largely copied onto the new strand by maintenance methyltransferases (DNMT1 in mammals, which recognizes hemi-methylated DNA after replication and methylates the new strand to match). Histone marks are propagated through a combination of parental histone redistribution to daughter DNA strands and "reader-writer" enzyme complexes that recognize existing marks on neighboring nucleosomes and copy them onto newly deposited histones. The result is a heritable, self-templating chromatin state, which is why liver cells reliably produce more liver cells and never spontaneously become neurons.
Step 5 — This regulatory state can be erased and reset, proving the underlying genome is intact. If the epigenetic marks are experimentally stripped away — as happens naturally in early embryos (global demethylation waves occur after fertilization and again in primordial germ cells) or artificially in a nuclear transplantation experiment — the nucleus reverts to a state capable of directing full development. This reversal is the direct experimental proof of genomic equivalence: you cannot reset a genome to totipotency if the genes required for other fates were physically deleted.
The evidence
Weismann's germ-plasm hypothesis and the need for a test (1892). August Weismann proposed that hereditary determinants might be unequally distributed to daughter cells during development, so that different cell lineages would progressively lose access to genetic material irrelevant to their fate. This was a coherent hypothesis at the time — chromosomes had only recently been described, and no one yet knew whether mitosis distributed genetic material equally. It made a clear, falsifiable prediction: differentiated cell nuclei should be functionally and quantitatively unequal, and should be incapable of directing full development if transplanted elsewhere.
Theodor Boveri's sea urchin experiments (1887–1904). Boveri showed that individual chromosomes carried distinct, non-interchangeable hereditary information (using dispermic sea urchin eggs and chromosome-deficient blastomeres), establishing the chromosome theory of heredity, and set the stage for asking whether the total chromosome complement changes during differentiation. His work, alongside Walther Flemming's cytological studies of mitosis, supported the idea that mitosis is a mechanism for exact, equal chromosomal distribution — arguing against Weismann's unequal-segregation model as a general rule, though it did not directly test differentiated nuclei.
Briggs and King: the first nuclear transplantation experiments (1952). Robert Briggs and Thomas King, working with the leopard frog Rana pipiens, developed a technique to transplant a nucleus from an early embryonic cell into an egg whose own nucleus had been destroyed or removed (an enucleated egg). Using a fine glass micropipette, they extracted a nucleus from a blastula-stage donor cell and injected it into an enucleated recipient egg. A significant fraction of these reconstructed eggs developed into normal, swimming tadpoles. This showed that the nucleus of an early embryonic cell retains full developmental potential — but blastula cells are only mildly differentiated, so the experiment did not yet answer whether fully differentiated cells retain a complete genome.
John Gurdon's serial and late-stage nuclear transplants (1958–1962). John Gurdon, working with the South African clawed frog Xenopus laevis, pushed the experiment further, using nuclei from progressively more differentiated donor cells — including fully differentiated intestinal epithelial cells from feeding tadpoles, identified unambiguously by the brush border characteristic of gut epithelium. He used ultraviolet light to destroy the nucleus of unfertilized Xenopus eggs (rather than physically removing it, which is technically harder), then microinjected a single donor somatic nucleus into each enucleated egg. Results, quantitatively:
- A meaningful fraction of eggs receiving intestinal epithelial nuclei developed at least to the swimming tadpole stage.
- Some proceeded all the way to sexually mature, fertile adult frogs — proof the transplanted nucleus retained every gene necessary for every tissue in a complete organism, including germ cells.
- Because success rates dropped with the degree of donor cell differentiation, Gurdon used serial transplantation: nuclei from partially developed clones were re-transplanted into fresh enucleated eggs to boost the overall yield of successes and rule out the alternative explanation that rare contaminating undifferentiated cells (not genuine differentiated intestinal nuclei) were responsible for the occasional successes.
- Clones derived from a single donor nucleus were genetically identical to one another and to the donor, confirmed using genetic markers (a nucleolar mutant strain lacking one copy of the ribosomal RNA genes was used as a lineage marker to prove the resulting frogs' nuclei really derived from the transplanted donor nucleus, not from residual host nuclear material).
What this proved. A fully differentiated somatic cell nucleus, when placed in the cytoplasmic environment of an unfertilized egg, can be reprogrammed to direct the complete development of a normal, fertile organism. This is only possible if that nucleus retained the entire genome — every gene required for neurons, muscle, blood, gonads — even though, in its original intestinal cell context, only a small subset of those genes was being transcribed. Differentiation therefore reflects a change in gene expression, reversible under the right cytoplasmic conditions, not an irreversible change in gene content. Gurdon shared the 2012 Nobel Prize in Physiology or Medicine with Shinya Yamanaka, whose induced pluripotent stem cell work extended the same principle using purely molecular (transcription factor) reprogramming rather than nuclear transplantation.
Dolly the sheep (1996, Ian Wilmut and Keith Campbell) provided the mammalian confirmation. Using a nucleus from an adult ewe's mammary gland cell, fused into an enucleated sheep oocyte by electrical pulse, Wilmut and Campbell's team at the Roslin Institute produced Dolly — the first mammal cloned from an adult somatic cell — demonstrating that genomic equivalence and reprogrammability extend to mammals, not just amphibians, though at very low efficiency (Dolly was the single success among 277 attempted nuclear transfers).
Worked examples
Example 1 — Interpreting a partial-success cloning experiment. Suppose a researcher repeats a Gurdon-style transplant in a hypothetical frog species. She transplants nuclei from three donor sources into enucleated eggs:
| Donor cell source | Eggs injected | Reached tadpole stage | Reached fertile adult |
|---|---|---|---|
| Blastula cell (undifferentiated) | 100 | 78 | 65 |
| Differentiated skin cell | 120 | 14 | 2 |
| Differentiated skin cell, serial transplant (2nd round) | 90 | 31 | 9 |
How should this be interpreted? The blastula-derived nuclei succeed at high frequency (65%), consistent with their minimal differentiation and largely "open" chromatin. The once-transplanted differentiated skin nuclei succeed rarely (1.7% to fertile adult) — not zero, which is the critical point: a nonzero success rate, even if low, demonstrates that at least some fully differentiated nuclei retain complete genomic information, since these are unambiguously derived from a single differentiated cell type. The low overall frequency reflects technical difficulty in fully erasing an established chromatin state (incomplete reprogramming), not evidence that the genome itself is incomplete. The improvement upon serial transplantation (9/90 = 10% for round 2 versus 2/120 ≈ 1.7% for round 1) is expected: nuclei that already demonstrated developmental competence in the first round are more likely to succeed again, enriching for correctly reprogrammed genomes and diluting out any rare artifact of contaminating undifferentiated donor cells. This experimental logic — rare successes plus serial enrichment — is exactly what let Gurdon rule out the objection that his early results might reflect stem-cell contamination in the donor tissue rather than genuine differentiated-nucleus totipotency.
Example 2 — Distinguishing genomic equivalence from a true exception (immunoglobulin gene rearrangement). A student observes that mature B lymphocytes contain immunoglobulin genes with a different DNA sequence structure than the same genes in skin or liver cells of the identical individual — segments of the variable (V), diversity (D), and joining (J) exons have been physically deleted and recombined (V(D)J recombination, mediated by the RAG1/RAG2 recombinase). Is this a violation of genomic equivalence? Reasoning it through: V(D)J recombination is a genuine exception, not a mere case of differential gene expression — the DNA sequence at the immunoglobulin locus is irreversibly altered by site-specific recombination early in B cell development, and this change is passed on to that cell's mitotic descendants (memory B cells, plasma cells) but not reversed. This means a mature B lymphocyte's genome is not, strictly, identical to the zygote's genome at this one locus. However, this is a narrow, deliberate exception restricted to a handful of loci in one lineage (B and T lymphocytes generate similar diversity via T-cell receptor gene rearrangement), evolved specifically to generate antibody diversity beyond what a fixed genome could encode. It does not undermine the general principle for the remaining ~20,000 genes in that same B cell, nor for the vast majority of the roughly 200 other cell types in the body, which retain the complete, unrearranged genome. Genomic equivalence is therefore a statement about the default developmental strategy — true almost everywhere — with lymphocyte receptor genes and mature mammalian erythrocytes (which extrude their nucleus entirely) standing as the clearest, most instructive exceptions.
Common misconceptions & traps
| Misconception | Why it's wrong |
|---|---|
| "Differentiated cells physically lose the genes they don't use." | False for nearly all cell types; genes are repressed (silenced via chromatin/methylation) but remain present in the DNA sequence, as nuclear transplant experiments directly demonstrate. |
| "Genomic equivalence means all cells are identical." | No — cells are epigenetically and transcriptionally distinct, sometimes dramatically. Genomic equivalence is specifically about DNA content, not about cell state or function. |
| "Gurdon's experiment worked every time." | Success rates were low, especially with fully differentiated donor nuclei; the significance lies in the fact that success occurred at all and could be rigorously attributed to a differentiated donor nucleus, not in a high yield. |
| "Since B cells rearrange their DNA, genomic equivalence is false." | Lymphocyte receptor gene rearrangement is a real, narrow exception; it doesn't overturn the principle for the genome as a whole or for other cell types. |
| "Epigenetic marks are permanent and unchangeable, unlike mutations." | Epigenetic marks are heritable through mitosis but are chemically reversible in principle — this reversibility is exactly what nuclear transfer and reprogramming exploit; mutations to DNA sequence are not reversible by the same cellular machinery. |
The scientist behind it
Origins · 1 minSir John B. Gurdon and how this was discovered
John Gurdon's path to this landmark work was, by his own account, an unlikely one — his school biology teacher famously rated him bottom of the class and considered a career in science "a sheer waste of time." Undeterred, Gurdon pursued zoology at Oxford and, as a doctoral student under Michail Fischberg in the late 1950s, took up the technically formidable challenge of nuclear transplantation in Xenopus laevis, the African clawed frog, chosen partly because its eggs are large, robust, and available year-round in the laboratory (unlike the seasonal Rana pipiens used by Briggs and King). Gurdon's technical innovation was as important as his biological question. Rather than physically excising the egg's nucleus with a needle (as Briggs and King had done, with high egg mortality), he used ultraviolet irradiation to destroy the maternal chromosomes in unfertilized Xenopus eggs, leaving the egg's cytoplasm intact and viable for microinjection of a donor nucleus via a fine glass pipette. This let him push the experiment to nuclei from increasingly specialized donor tissues, culminating in his celebrated 1962 demonstration that nuclei from fully differentiated, terminally specialized intestinal epithelial cells of feeding tadpoles could support complete, normal, fertile frog development after transplantation. The result overturned decades of uncertainty about whether differentiation involved permanent, irreversible genetic restriction. It reframed differentiation as a problem of gene regulation, laid the conceptual foundation for animal cloning (used two decades later to produce Dolly the sheep), and directly inspired Shinya Yamanaka's 2006 discovery that four transcription factors (Oct4, Sox2, Klf4, c-Myc) could reprogram adult mouse fibroblasts into induced pluripotent stem cells without any need for an egg at all. Gurdon and Yamanaka jointly received the 2012 Nobel Prize in Physiology or Medicine "for the discovery that mature cells can be reprogrammed to become pluripotent."
Origins · 1 minhow this was discovered
Where this matters today
Reproductive and research cloning. Somatic cell nuclear transfer (SCNT), the direct descendant of Gurdon's protocol, is used to clone livestock with valuable genetic traits, to preserve endangered species by using surrogate closely related species as egg donors and recipients, and to generate genetically matched research animal models.
Induced pluripotent stem cell (iPSC) technology. Because genomic equivalence guarantees that an adult skin or blood cell nucleus retains every gene needed for any other cell type, Yamanaka-factor reprogramming can convert a patient's own cells into pluripotent stem cells, which can then be differentiated into cardiomyocytes, neurons, or pancreatic beta cells for disease modeling, drug screening, and prospective regenerative therapies — all without the immune-rejection or ethical concerns associated with embryonic stem cells.
Cancer biology. Tumor cells frequently exhibit epigenetic dysregulation (aberrant DNA methylation, loss of Polycomb-mediated silencing) rather than, or in addition to, mutation — understanding that gene silencing is reversible has motivated an entire drug class, epigenetic therapies (DNA methyltransferase inhibitors such as azacitidine, histone deacetylase inhibitors such as vorinostat), used clinically in myelodysplastic syndrome and certain lymphomas.
Agricultural biotechnology. Cloning of elite dairy cattle, disease-resistant pigs, and other livestock exploits the same nuclear transfer logic Gurdon established, now routinely performed using adult somatic donor cells rather than embryonic ones.
Conservation biology. Genomic equivalence underlies proposals (and some successful attempts) to clone critically endangered or even recently extinct species from preserved somatic cell lines, using nuclear transfer into oocytes of a closely related surrogate species.
Basic understanding of <a class="wiki-link" href="/wiki/bio-devo-determination-vs-differentiation" data-track="wiki_article.body.wiki_link">Cell Determination and Differentiation</a> and <span class="wiki-link-missing">Differential Gene Expression</span>. Genomic equivalence is the conceptual bedrock that makes the entire modern framework of transcriptional regulation, chromatin biology, and epigenetics comprehensible: none of it would matter if cells simply discarded unneeded genes, and understanding that they don't is what makes questions about how genes are selectively silenced and activated worth asking in the first place, foreshadowing Nuclear Reprogramming and Cloning as a direct technological application.
Ask the tutor: How does the cytoplasm of an enucleated egg actually erase a differentiated nucleus's chromatin marks during reprogramming?
Does genomic equivalence mean every single cell in the body has identical DNA?
Almost, but not quite — it's a strong general rule with well-defined exceptions. The great majority of somatic cells (skin, muscle, neurons, liver, etc.) retain a genome sequence essentially identical to the zygote's. Notable exceptions include mature mammalian red blood cells, which extrude their nucleus entirely during maturation and so have no DNA at all; B and T lymphocytes, which permanently rearrange their antigen-receptor gene segments via V(D)J recombination; and some invertebrates (certain nematodes, copepods) that undergo programmed chromatin diminution, physically deleting portions of the genome in somatic lineages while germline cells retain the full complement. These exceptions are narrow and well-characterized, and they don't undermine the principle as the dominant developmental strategy across animals and plants.
If all cells have the same genes, why don't they all look and behave the same?
Because having a gene and expressing it are entirely different things. A gene must be transcribed into mRNA and translated into protein to have any effect on cell structure or function, and transcription is controlled by regulatory DNA sequences (promoters, enhancers) bound by transcription factors, whose availability differs from cell to cell. A liver cell and a neuron both possess the albumin gene and the gene for a particular sodium channel, but only the liver cell's transcription factor environment activates albumin production, and only the neuron's environment activates the channel gene. Layered on top of transcription factor binding are stable chromatin modifications (DNA methylation, histone marks) that lock in these expression patterns across cell division, which is why a liver cell reliably makes more liver cells.
How exactly did Gurdon prove the new frogs came from the donor nucleus and not some leftover host material?
He used a genetic marker system. Some of his donor and host frog strains carried a mutation affecting the nucleolus (the site of ribosomal RNA gene clusters) — nucleolar mutant frogs have one fewer nucleolus per cell than wild type because they carry only one functional copy of the ribosomal RNA gene cluster. By transplanting nuclei from a nucleolar mutant donor strain into enucleated eggs from a wild-type strain (and vice versa), Gurdon could examine the nucleolar number in cells of the resulting tadpoles and frogs under the microscope. If the offspring's cells showed the donor's nucleolar phenotype rather than the host's, this proved development had been directed by the transplanted donor nucleus, not by any residual host nuclear material accidentally left behind during the enucleation procedure.
Is genomic equivalence the same thing as pluripotency?
No, though they are closely related. Genomic equivalence is a statement about DNA content — that a cell's genome contains the full set of genes needed for any cell type in the organism. Pluripotency (or totipotency) is a statement about functional developmental potential — that a cell's current regulatory state allows it to actually differentiate into many (or all) cell types when given the right signals. A fully differentiated skin cell is genomically equivalent to a stem cell (same DNA content) but is not pluripotent in its native state, because its chromatin and transcription factor profile restrict it to producing more skin cells. Reprogramming technologies (nuclear transfer, Yamanaka factors) work precisely because they can convert a genomically equivalent but functionally restricted cell into a pluripotent one, by resetting its regulatory state rather than adding missing genes.
How does genomic equivalence relate to induced pluripotent stem cells (iPSCs)?
iPSC technology is essentially a molecular substitute for Gurdon's egg cytoplasm. Shinya Yamanaka showed in 2006 that forcing expression of just four transcription factors — Oct4, Sox2, Klf4, and c-Myc — in an adult mouse fibroblast is sufficient to reprogram its chromatin and transcriptional state back to a pluripotent, embryonic-stem-cell-like condition, without needing to place the nucleus inside an egg at all. This only works because the fibroblast's genome, per genomic equivalence, still contains every gene required for pluripotency and for every downstream cell fate; the four factors simply re-establish the correct regulatory network and reverse the repressive epigenetic marks that had locked the cell into the fibroblast state. Gurdon and Yamanaka shared the 2012 Nobel Prize precisely because their work together established both halves of this logic — the genome is retained, and the regulatory state on top of it is reversible.
Why couldn't Briggs and King's original 1952 experiment fully settle the question of genomic equivalence?
Briggs and King used nuclei from blastula-stage embryonic cells, which are only mildly differentiated — they had not yet committed to specialized fates like muscle, nerve, or gut. Their high success rate showed that early embryonic nuclei retain full developmental potential, but a skeptic could reasonably argue this says little about fully differentiated, terminally specialized cells, which might plausibly have undergone irreversible genetic restriction even if blastula cells had not. It took Gurdon's use of unambiguously differentiated donor tissue — intestinal epithelial cells identified by their distinctive brush border, taken from feeding tadpoles well past the point of overt specialization — combined with serial transplantation controls, to close this gap and demonstrate genomic equivalence even in a fully differentiated somatic cell type.
Does this principle apply to plants as well as animals?
Yes, and in some ways plants provide an even more dramatic demonstration. Frederick Steward's experiments in the 1950s–1960s showed that single differentiated carrot root (phloem) cells, when cultured in a nutrient medium containing coconut milk, could dedifferentiate and grow into complete, fertile carrot plants — a phenomenon called totipotency in plants, directly paralleling Gurdon's animal results and in fact predating them in some respects. Plant genomic equivalence underlies modern plant tissue culture and micropropagation techniques used throughout horticulture and agricultural biotechnology, where a small piece of differentiated plant tissue can be induced to regenerate an entire new plant.