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John Doebley studies the genetics of changes in plant form, especially the domestication of maize from teosinte. His own research profile describes quantitative genetics as a principal approach.^[ref]

In 1997, Doebley and colleagues identified teosinte branched1 as a regulator associated with the stronger apical dominance of maize. Higher expression in maize connected altered gene regulation to reduced lateral branching. This work made a major crop difference experimentally approachable as a change in a developmental programme rather than an inexplicable difference between two plant forms.^[ref]

A PNAS biographical profile includes a labelled photograph taken in 2003.

Researcher in cancer genetics. Donehower and collaborators found that mice lacking p53 could develop but were susceptible to spontaneous tumours, providing experimental evidence for a role in tumor suppression.^[ref]

Lucas Janson studies high-dimensional statistics and statistical machine learning, with scientific collaborations in genetics, climatology and political science. His current Stanford homepage describes this combination of methodological research and applications.^[ref]

He coauthored distillation for the conditional randomization test. Its computational motivation is that a powerful test statistic may involve expensive machine learning; distillation avoids repeating the most costly fitting step for every conditional resample.^[ref]

Researcher in human genetics. Koch and collaborators linked skeletal-muscle chloride channel defects with dominant and recessive myotonia congenita, connecting an inherited disease pattern with a molecular candidate mechanism.^[ref]

Researcher in ciliate genetics. Cervantes and collaborators investigated how Tetrahymena thermophila selects a mating type through joining and deletion of gene segments, connecting developmental genome rearrangement with reproductive identity.^[ref]

Researcher in molecular genetics and coauthor of the Meselson-Stahl experiment. Following isotopically labeled DNA across generations connected the distribution of old and new material with the mechanism of DNA replication.^[ref]

Researcher in microbial genetics. With Salvador Luria, Delbrück analyzed variation in virus resistance among bacterial cultures, connecting fluctuations in resistant-cell numbers with mutations arising before selection.^[ref]

Researcher in evolutionary genetics. Melissa M. Gray and collaborators investigated rapid, extreme body-size change in island mice, connecting an unusual natural phenotype with its inherited determinants.^[ref]

Nasonia is a genus of small parasitoid wasps used in research on genetics, speciation and host interactions. Developing offspring exploit a host animal rather than merely sharing its environment. Nasonia vitripennis and Nasonia giraulti support comparisons between related species.

Originality lay chiefly in an explanatory mechanism and a sustained evidential synthesis, rather than in the first suggestion that living forms might change. Charles Darwin combined existing problems and resources in a new way, while Alfred Russel Wallace's independent work prevents the mechanism of natural selection from being assigned to a wholly solitary origin.

Jean-Baptiste Lamarck had already offered a connected account of the transformation of living forms. His explanation gave substantial roles to changed circumstances, altered habits, use and disuse, and the transmission of acquired modifications. This was a serious attempt to explain organic change, not simply the absurd proposition that an animal obtains anything it wishes for. Nevertheless, a process that transforms individuals through altered activity differs from differential persistence and reproduction among variants. Recognizing that difference allows comparison without pretending that every earlier idea of evolution was already natural selection.^[ref]

Charles Darwin also drew on practices that were not inventions of an isolated theorist. Breeders' artificial selection demonstrated that cumulative choice among inherited differences could alter domestic forms. Thomas Robert Malthus's population argument made unrestricted multiplication and limited subsistence a problem requiring explanation. Geology, the fossil record and the geographical distribution of organisms supplied historical and spatial patterns that a theory of species had to address. None of these ingredients alone entailed Charles Darwin's conclusion. A population check might eliminate individuals without producing cumulative adaptive change; breeding involved a human chooser whose intentions could not simply be projected into nature.^[ref]

The distinctive inference joined inherited differences to unequal success in leaving descendants. If some variants leave more surviving offspring under particular conditions, and some relevant differences recur in their descendants, the composition of a population can change over successive generations. Natural selection consequently requires neither an organism's foresight nor a breeder intentionally specifying its destination. Competition also has a wider meaning than physical combat: it includes dependence on other organisms and on conditions necessary for reproduction. In this way an apparently purposive fit between organism and environment could be given a historical explanation.^[ref]

Charles Darwin's larger contribution was to make that process part of a theory of branching common descent. Divergence, extinction, the affinities used in classification, the distribution of organisms on islands and continents, and similarities of structure could be treated as connected consequences of a history of descent with modification. The argument accumulated partially independent kinds of evidence. It did not rest on displaying one adaptation and declaring that the rest of organic history must follow. It also openly discussed difficulties, including complex organs, hybridism and imperfections in the fossil record.^[ref]

The case of Alfred Russel Wallace is decisive for judging intellectual priority. In the Introduction to the 1859 On the Origin of Species by Charles Darwin, Charles Darwin explicitly acknowledged the arrival of Alfred Russel Wallace's memoir and the publication of their materials together. Alfred Russel Wallace's essay on varieties departing from the original type argued that struggle could favour particular variants and permit continuing divergence. Its later reprint identifies the 1858 publication and distinguishes that essay from subsequent additions to the collected volume.^[ref][ref] Independent convergence shows both that the mechanism was a real intellectual achievement and that the surrounding problems and observations were not private possessions.

Finally, the historical theory must be distinguished from later genetics. Charles Darwin did not possess a Mendelian explanation of heredity, and the 1859 book allowed roles for use and disuse and other causes of variation. It is therefore inaccurate to identify its entire content with a modern opposition between strictly genetic natural selection and a wholly separate Lamarckian alternative.^[ref] The qualified judgment is that Charles Darwin produced an unusually powerful synthesis and a major new causal argument, independently paralleled by Alfred Russel Wallace. Dependence on predecessors limits a claim of creation from nothing; it does not reduce the theory to the repetition of those predecessors.

A small single-stranded-DNA bacteriophage used in molecular-genetics research. Its compact genome made it useful for testing relationships among sequence, genetic organization and viral function.

Researcher in yeast genetics and RNA polymerases. Thuriaux and collaborators identified RPA43 as encoding an essential subunit of RNA polymerase I; gene disruption and rescue experiments connected the subunit with ribosomal-RNA synthesis.^[ref]

A population geneticist studies variation in allele frequencies, its evolutionary causes and the ancestry of sampled genetic material. The work combines genetics, probability and empirical data to investigate processes including natural selection, genetic drift and gene flow. For example, comparing alternative demographic models can test whether an observed pattern is better explained by biological population separation or continuing exchange, subject to the model assumptions. ^[ref]

Researcher in cardiac genetics. Wang and collaborators identified voltage-gated sodium channel mutations in patients with long QT syndrome, connecting an inherited cardiac rhythm disorder with changes in a specific molecular channel.^[ref]

Robin Holliday was a researcher in genetics and cell biology whose contributions include the proposed recombination intermediate now called the Holliday junction. His work also concerned DNA methylation and the control of biological development.^[ref]

His 1964 paper proposed a molecular mechanism for gene conversion. Exchange of strands between related DNA molecules produces a joint intermediate and regions of heteroduplex DNA; movement of the junction, called branch migration, extends the exchanged region. Different ways of resolving the joint structure give different arrangements of flanking genetic markers.^[ref]

For an illuminating example, follow a marker on each side of the exchanged region. One resolution can retain their original outside pairing, while another exchanges the flanking regions. The model therefore links an invisible molecular intermediate to different observable inheritance patterns. It was a mechanistic proposal, not a claim that every modern case of gene conversion must follow exactly one pathway.

Ronald J. Konopka coauthored the 1971 identification of circadian rhythm mutants in Drosophila melanogaster with Seymour Benzer. Their screen produced arrhythmic, short-period and long-period flies. The combination showed that a mutation can alter the period of an internal timing mechanism, rather than only disabling movement altogether.^[ref]

Automatic collection measured when adults emerged, and infrared detectors measured individual locomotion. Tests in constant darkness separated free-running timing from direct light-driven activity. Mapping and complementation indicated that the three mutations affected the same functional gene on the X chromosome, providing an entry point for the genetics of biological clocks.^[ref]

Saccharomyces cerevisiae is a particular species of yeast, used in baking, brewing and laboratory research. During ordinary vegetative growth it reproduces by budding: a smaller daughter grows from the mother before separation. Laboratory strains can be maintained as either haploid or diploid biological cells. This makes it possible to investigate genes in a single eukaryote, then use controlled crosses and meiosis to connect a genotype to a phenotype. See Burgess, Powers and Mell, Budding Yeast Saccharomyces cerevisiae as a Model Genetic Organism (2017), pp. 1–2.

The practical value of Saccharomyces cerevisiae as a model organism is the combination of easy laboratory cultivation, accessible genetics, and cellular functions shared with other eukaryotes. A haploid strain has one set of chromosomes, so a changed allele is not accompanied by a second copy at that genetic locus. But a mutation need not produce an observable phenotype under every condition. The yeast is also a whole organism, not a miniature human: transferring a result requires evidence that the relevant function is shared in the target system. See Duina, Miller and Keeney, Budding Yeast for Budding Geneticists (2014): cultivation, genetic tools and conserved functions.

For a concrete example, Hartwell, Culotti and Reid's 1970 work followed temperature-sensitive Saccharomyces cerevisiae strains with successive microscope photographs. Failure to complete a particular part of the cell cycle helped identify required gene functions. Their distinction between when a function is required and where a cell finally stops is especially instructive: the visible endpoint need not be the time of the underlying defect. See Hartwell, Culotti and Reid, Genetic control of the cell-division cycle in yeast. I. Detection of mutants (1970): primary abstract. This is a useful way to turn an observable change in a biological cell into a question about genes and causal order.

In alcoholic fermentation, Saccharomyces cerevisiae converts sugars into ethanol and carbon dioxide. The carbon dioxide helps dough rise; the ethanol is useful in alcoholic drinks. The metabolism also supports production of ATP, a usable cellular energy carrier. This is one metabolic ability of one species, not the definition of every yeast. See Clark, Douglas and Choi, Biology 2e, 7.5: alcohol fermentation and the Burgess, Powers and Mell account above.

For glucose, the ideal net stoichiometry isOne molecule of glucose supplies six carbon chemical atoms: four end up in the two ethanol molecules and two in the two carbon dioxide molecules. The twelve hydrogen and six oxygen chemical atoms also balance. This is a net material balance across several enzyme-catalyzed steps, not a single chemical reaction step or the complete bookkeeping for cellular energy carriers. The standard pathway accounting yields a net two ATP per glucose: the initial breakdown produces the ATP, while the later conversion to ethanol regenerates a coenzyme needed to keep the breakdown going. See Clark, Douglas and Choi, Biology 2e, 7.2: net ATP accounting and the section 7.5 cited above.

At complete conversion, this toy gives $20\mathrm{mmol}$ of ethanol and $20\mathrm{mmol}$ of carbon dioxide. The carbon balance is $6\times 10=2\times 20+1\times 20=60\mathrm{mmol}$ of carbon chemical atoms. A real culture also builds cellular material, can use other metabolic routes, and may retain dissolved carbon dioxide; the toy is a reference balance rather than a prediction of collected gas or beverage yield.

Although alcoholic fermentation does not require molecular oxygen as a reactant, the presence of molecular oxygen does not force Saccharomyces cerevisiae to stop fermenting. De Deken's 1966 experiments reported predominantly fermentative glucose use during exponential growth in air. Consequently, bubbles do not establish either absence of molecular oxygen or an exclusively fermentative metabolism. See De Deken, The Crabtree Effect: A Regulatory System in Yeast (1966): primary abstract.

Sarah J. Liljegren is a researcher in plant development and genetics. In a 2000 collaborative study, she investigated how the SHATTERPROOF genes SHATTERPROOF1 and SHATTERPROOF2 control fruit dehiscence, the opening of a mature fruit that releases its seeds. These genes encode MADS-box transcription factors and help specify the tissues where the fruit opens.^[ref]

The comparison between single and double mutants is illuminating. Disabling either SHATTERPROOF1 or SHATTERPROOF2 alone produced no new visible phenotype, while disrupting both impaired normal fruit dehiscence. This is an example of genetic redundancy: an experiment on only one gene could miss a shared developmental function. The combined mutant and constitutive-expression experiments connected these genes with the differentiation of the opening zone and lignin deposition in neighboring cells, linking gene activity to the mechanics of seed dispersal.^[ref]

Seymour Benzer helped turn the study of behavior into an experimental problem in genetics. With Ronald J. Konopka, he reported fruit-fly mutations that abolished daily rhythmicity or changed its period to approximately 19 or 28 hours. Both adult emergence and individual locomotor activity were affected.^[ref]

Flies were tested in constant darkness, while infrared monitoring recorded individual movement without imposing a daily light cycle. Persistence of altered timing under those conditions supported an internal circadian rhythm mechanism, rather than merely a different immediate response to the lamps switching on. The mutations mapped to the same functional gene on the X chromosome.^[ref]

Stewart Shuman is a biochemist who investigates how enzymes modify and repair nucleic acids. His laboratory combines biochemistry, structural biology and genetics to connect a particular chemical reaction with the protein machinery that performs it.^[ref]

With Anupam K. Chakravarty, Shuman tested competing reaction mechanisms for the RNA ligase RtcB. The question concerned the chemistry of the broken RNA ends: did a cyclic phosphate join directly to an opposing hydroxyl end, or did opening and activation precede sealing? Their 2012 experiments supported a GTP-dependent pathway involving hydrolysis, activated reaction intermediates and formation of a new phosphodiester bond.^[ref]

The logical force of such an experiment can be seen without assuming that a successful final reaction reveals every step. Suppose mechanisms A and B both predict a joined RNA molecule, but A requires GTP even when the starting end already contains a cyclic phosphate, whereas B predicts that this substrate bypasses the GTP requirement. Comparing otherwise equivalent reactions with and without GTP distinguishes those predictions. Detecting an intermediate also requires attention to chemical kinetics: a species appearing only after product accumulation cannot explain an earlier obligatory step. These are general reasons to combine selective changes in starting chemistry with time-resolved measurements, rather than identifying a reaction mechanism solely from the final product.