146 Fun Facts About DNA

What does DNA stand for?

DNA stands for deoxyribonucleic acid; the 'deoxy' refers to its sugar, 2-deoxyribose, which is ribose missing one oxygen atom.

Which living ape, along with the bonobo, is humanity's closest relative by DNA?

Chimpanzee DNA is almost 99% identical to ours where the two can be lined up, yet that small gap still adds up to tens of millions of single-letter differences built up over about six million years.

Which three components make up a single DNA nucleotide?

Base, sugar, and phosphate group: the sugars and phosphates link into each strand's backbone, so only the order of the bases is left to carry the genetic message.

Which base takes thymine's place in RNA?

Uracil takes thymine's place in RNA; a likely reason DNA uses thymine instead is that cytosine can decay into uracil, so a distinct base lets repair enzymes spot the damage.

In a DNA molecule, Adenine (A) always pairs with which other base?

Adenine always pairs with thymine; Erwin Chargaff found in the late 1940s that DNA's amounts of A and T, and of G and C, are always equal, a clue Watson and Crick used.

What is the primary function of DNA in living organisms?

To store and pass on genetic information; some viruses break the rule and use RNA as their genetic material instead.

Which physicist's 1944 book What Is Life? inspired both Watson and Crick to study the gene?

Erwin Schrödinger, of the famous cat, argued that heredity must be written into an 'aperiodic' solid, a molecule whose structure holds a code; Watson and Crick each named the book as an inspiration.

Which journal published Watson and Crick's 1953 paper on DNA's structure?

Nature ran the paper on 25 April 1953, little more than a page long, alongside two others carrying the supporting X-ray data, one of them co-written by Rosalind Franklin.

Which organelle of plant cells carries its own small genome, a relic of once free-living bacteria?

Chloroplasts descend from a photosynthetic bacterium that was engulfed by an early cell; they still carry DNA of their own, separate from the rest of the plant's.

Unlike DNA, RNA is typically found in what form?

Single-stranded RNA can still fold back on itself into short double-stranded hairpins, which is how transfer RNA gets its cloverleaf shape.

According to the central dogma of molecular biology, what is the general flow of genetic information?

Information flows DNA → RNA → protein; Francis Crick first stated the idea in 1957, and retroviruses later showed it can also flow from RNA back into DNA.

What term describes DNA copying, in which each new molecule keeps one of the original strands?

Semi-conservative copying was confirmed in 1958 by Meselson and Stahl, whose experiment ruled out the rival ideas that the old strands stay together or are scattered in pieces.

What is the process of building a protein from an RNA template called?

Translation takes place on ribosomes, and antibiotics such as tetracycline work by jamming the ribosomes of bacteria.

What is the unit of DNA wound around a core of eight histone proteins called?

A nucleosome wraps about 147 base pairs, nearly two turns of double helix, around eight histones; the beads-on-a-string chain they form is how two metres of DNA fit in each cell.

What is the name for an agent, such as certain chemicals in tobacco smoke, that causes changes in DNA?

Mutagens range from chemicals to radiation such as X-rays; because the DNA changes they cause can lead to cancer, many of them are also carcinogens.

What are small, circular DNA molecules in bacteria that replicate independently called?

Plasmids often carry antibiotic-resistance genes and can pass from one bacterium to another, even across species, which helps drug resistance spread so fast.

Which fruit is a classroom favourite for extracting DNA because each cell carries eight copies of its genome?

Strawberry cells are octoploid, with eight sets of chromosomes where ours have two, so a mashed berry mixed with detergent and alcohol yields a clump of DNA big enough to see.

Which of these can tell identical twins apart?

Fingerprints are shaped by conditions in the womb as well as by genes, so identical twins, whose DNA profiles match, end up with different ridge patterns.

Who first isolated 'nuclein', now known as DNA, in 1869?

Friedrich Miescher was studying the proteins of cells when he found a substance rich in phosphorus that behaved like no protein he knew.

What is the name for the enzyme that separates DNA's two strands during replication?

Helicase unzips the two strands using energy from ATP; a faulty human helicase causes Werner syndrome, a disorder of premature ageing.

What does a 'silent' point mutation refer to?

A silent mutation leaves the encoded amino acid unchanged; because most amino acids are specified by several codons, many third-position (wobble) changes have no effect on the protein.

Which type of RNA carries a gene's instructions to the ribosomes for protein synthesis?

Messenger RNA (mRNA) is what the Pfizer and Moderna COVID-19 vaccines deliver: a synthetic strand that tells cells to make the virus's spike protein and is broken down within days.

What is the primary role of DNA polymerase during DNA replication?

Building new strands from nucleotides works only by extending an existing strand, which is why each new strand has to begin with a short stretch of RNA.

What is folding DNA into nanoscale shapes using complementary base pairing called?

DNA origami was unveiled in 2006 by Caltech's Paul Rothemund, who folded a long viral DNA strand into shapes such as smiley faces using more than 200 short 'staple' strands.

What dismissive nickname was long given to the stretches of DNA that don't code for proteins?

Junk DNA is not all junk: some of these non-coding stretches turned out to be switches that control when and where genes are turned on.

In the film Jurassic Park, gaps in the dinosaurs' DNA are patched with DNA from which animals?

Frogs: the borrowed amphibian DNA is the story's explanation for how the park's all-female dinosaurs manage to change sex and start breeding.

What is the process called when RNA is used as a template to synthesize DNA, as retroviruses do?

Reverse transcription is the step HIV depends on, which is why many antiretroviral drugs are reverse transcriptase inhibitors.

Which of these organisms carries roughly five times as much DNA in each cell as a human?

An onion is the star of the 'onion test', biologists' reminder that the amount of DNA an organism carries says little about how complex it is.

Angelina Jolie's 2013 essay about her preventive surgery put which cancer-risk gene in the headlines?

BRCA1 normally helps repair damaged DNA, so a faulty copy sharply raises the risk of breast and ovarian cancer; Jolie's doctors put her own breast-cancer risk at 87%.

What do you call the DNA-and-histone complex that condenses into chromosomes?

Chromatin packs tightly where genes are switched off and loosens where they are active, which helps the same DNA behave differently in different cell types.

Which enzyme lays down the short RNA starter that every new DNA strand begins with?

Primase is needed because DNA polymerase can only extend an existing strand; the short RNA starters it makes are later removed and replaced with DNA.

In 1994 Leonard Adleman used strands of DNA in a test tube to build the first working what?

Computer: Adleman's DNA strands tried out every route through a seven-point network at once to solve a path-finding puzzle; he is also the 'A' in RSA encryption.

Which Caltech chemist proposed a mistaken triple-helix model of DNA weeks before Watson and Crick's breakthrough?

Linus Pauling, later the winner of two Nobel Prizes, published his three-stranded model with Robert Corey in early 1953; within weeks the double helix had replaced it.

Which mutation type inserts or deletes nucleotides in a number not divisible by three?

A frameshift mutation is an insertion or deletion not divisible by three; because the code is read in triplets, every codon after it is re-grouped and the protein is garbled.

Which enzyme joins DNA fragments, notably Okazaki fragments, during DNA replication?

DNA ligase seals the gaps between Okazaki fragments on the lagging strand, and biologists borrow the same enzyme as molecular glue when joining pieces of DNA in the lab.

How many chromosomes does a normal human body cell contain in total?

46 chromosomes in 23 pairs; the other great apes have 48, because two ancestral chromosomes fused end to end to form human chromosome 2.

Which 1997 film imagines a future in which people's careers are decided at birth by their DNA?

Gattaca follows Vincent, conceived naturally and judged genetically unfit, who borrows the identity of a genetically favoured 'valid' man to win a place on a space mission.

What are the protective caps at the ends of chromosomes that shorten each time a cell divides?

Telomeres act as a countdown: once they wear down too far the cell can no longer divide, one reason our tissues wear out with age.

Which molecular biology technique uses short DNA primers to amplify a specific segment of DNA?

Polymerase chain reaction (PCR) copies a chosen DNA segment through repeated cycles of heating and cooling; Kary Mullis shared the 1993 Nobel Prize in Chemistry for devising it.

Which weak bonds between paired bases hold DNA's two strands together, yet let them unzip for copying?

Hydrogen bonds are individually weak, so enzymes can unzip the two strands, while much stronger covalent bonds keep each strand's own backbone intact.

Which non-coding stretch of a gene is cut out of the RNA copy during splicing?

Introns are cut out before the message is used, and the exons that remain can be joined in different combinations, letting one gene make several proteins.

What is the deliberate alteration of an organism's genes using laboratory technology called?

Genetic engineering produced its first modified bacterium in 1973, and by 1982 engineered bacteria were making human insulin, largely replacing hormone taken from pig and cow pancreases.

In a eukaryotic cell, where is most of the DNA kept, packed into chromosomes?

Nucleus, the cell's control centre, holds nearly all its DNA; bacteria have no nucleus at all, so their DNA sits loose in a region called the nucleoid.

What technique is used to determine the exact order of nucleotide bases in a DNA molecule?

DNA sequencing has collapsed in cost: the first human sequence took 13 years and billions of dollars, while by the early 2020s a person's DNA could be read for under $1,000.

What is DNA made by splicing together fragments from different organisms, such as a human gene in a bacterium?

Recombinant DNA is how most insulin has been made since the 1980s: the human gene is put into bacteria or yeast, which churn out the hormone in vats.

Which enzyme copies a DNA strand's sequence into RNA during transcription?

RNA polymerase is the target of the death cap mushroom's poison, which jams the enzyme so that cells can no longer read their genes.

Which amino acid does the start codon AUG specify?

AUG codes for methionine and doubles as the start signal, so nearly every newly made protein begins with it; bacteria use a modified form, formylmethionine, to start.

Which human cell type throws out its DNA as it matures and carries none at all?

Red blood cells eject their DNA as they mature, leaving more room for oxygen-carrying haemoglobin; the red cells of birds, by contrast, keep theirs.

What kind of point mutation swaps one amino acid for another in the resulting protein?

A missense mutation causes sickle cell disease: one base change turns a glutamic acid into a valine in haemoglobin.

At which London college was Photo 51, the famous X-ray image of DNA, taken in May 1952?

King's College London is where Rosalind Franklin and her PhD student Raymond Gosling took the image; it was simply the 51st diffraction photograph in the series.

In 1869, DNA was first isolated from material collected from what?

Used surgical bandages from a nearby clinic supplied pus rich in white blood cells; the Swiss doctor who washed the cells off them named the new phosphorus-rich substance 'nuclein'.

Which duo used E. coli's lactose system to show how cells switch enzymes on and off?

Jacob and Monod showed that a repressor protein keeps the lactose-digesting genes switched off until the sugar arrives, work that won the French pair a share of the 1965 Nobel.

Which effort to read all human DNA was declared complete in 2003?

The Human Genome Project finished two years ahead of schedule, yet its 'complete' read-out covered only about 92% of the DNA; the last gaps took roughly two more decades to close.

Which world leader joined Bill Clinton to announce the draft human DNA sequence in June 2000?

Tony Blair shared the 26 June 2000 announcement because Britain, through the Wellcome Trust, was a leading partner in the international project.

Craig Venter launched which firm in 1998 to race the publicly funded human DNA project?

Celera Genomics bet that a faster 'shotgun' method could outpace the public project, which sped up in response; the rivals ended up announcing their drafts together in 2000.

Roughly how many base pairs make up one full set of human DNA?

3.1 billion, and because nearly every cell carries two sets, one from each parent, the real count per cell is about 6.2 billion base pairs.

Roughly how many protein-coding genes does the human reference sequence contain?

About 20,000 is far lower than biologists once expected: estimates were revised downward again and again as the DNA was read more closely, settling at 19,000 to 20,000.

Which human chromosome is the smallest, and present in three copies in Down syndrome?

Number 21 is smaller than chromosome 22 despite the numbering: chromosomes were numbered by apparent size, and only later was 21 found to be the smallest.

Mitochondrial DNA is normally inherited from which parent?

The mother, because mitochondria travel in the egg cell; 'Mitochondrial Eve' is the woman all living humans trace back to this way.

Which royal family's remains were identified in the 1990s with help from Prince Philip's mitochondrial DNA?

The Romanovs, shot in 1918, lay in an unmarked grave until 1991; Philip was a great-nephew of Tsarina Alexandra, and his DNA matched hers and her children's.

Where was Alec Jeffreys working when he discovered DNA fingerprinting in 1984?

Alec Jeffreys was at the University of Leicester; his 'eureka moment' came on 10 September 1984 from an X-ray film showing family resemblances in his technician's DNA.

Who was the first person convicted of murder using DNA profiling, sentenced in 1988?

Colin Pitchfork was caught after a workmate admitted giving a blood sample in his place; the same DNA testing had first cleared a teenager who had confessed.

Which English king's skeleton, found under a car park in 2012, was confirmed by matching mitochondrial DNA?

Richard III, killed in battle in 1485, was matched to two distant living relatives; the skeleton also showed battle wounds and a sharply curved spine.

Which DNA-testing group did Barry Scheck and Peter Neufeld found in 1992?

The Innocence Project has helped free or exonerate hundreds of people since 1992, and its work has helped pass reforms in both state and federal law.

Which genealogy website did police publicly credit in 2018 with leading them to the Golden State Killer?

GEDmatch, a free open-upload site, was the one police named in 2018; a 2020 Los Angeles Times investigation found they had also quietly searched FamilyTreeDNA and MyHeritage.

Which US agency created and maintains CODIS, the national DNA database?

The national tier went live in October 1998; the FBI gave its software free to state and local labs to keep everyone on one system.

The heat-proof enzyme that made PCR practical comes from bacteria first found in which US national park?

Yellowstone's hot springs yielded the bacterium Thermus aquaticus in the 1960s; its Taq polymerase survives the high temperatures of every PCR cycle, so it replaced the E. coli enzyme first used.

Which American biochemist shared the 2020 Nobel Prize in Chemistry with Emmanuelle Charpentier for CRISPR gene editing?

Jennifer Doudna and Charpentier showed in 2012 that a bacterial defence system could be reprogrammed to cut DNA at a chosen spot, the 'genetic scissors' now used to rewrite genes.

Which British biochemist won two Nobel Prizes in Chemistry, the second for a method of reading DNA?

Frederick Sanger won in 1958 for working out the exact structure of insulin and again in 1980 for his way of reading DNA letter by letter, the method used for most of the first human genome.

The 1958 Meselson–Stahl experiment labelled DNA with a heavy isotope of which element?

E. coli grown on nitrogen-15 then switched to nitrogen-14 produced hybrid-density DNA, confirming that each new molecule keeps one old strand.

The 1952 Hershey–Chase phage experiments are also known by what appliance nickname?

The Blender experiment used an ordinary kitchen blender to shake the empty virus coats off infected bacteria, showing that the DNA left inside, not the protein, carried the genes.

In the Hershey–Chase experiment, radioactive sulfur-35 was used to label what?

Viral protein contains sulfur but DNA does not, while phosphorus-32 marked the DNA; it was the phosphorus label that passed into the bacteria and on to the next generation of viruses.

Who led the 1944 team that showed DNA is the 'transforming principle'?

Oswald Avery's team purified the substance that turned a harmless bacterial strain deadly and found it was DNA; nominated for a Nobel for decades, he never won one.

Griffith's 1928 transformation experiment in mice used which bacterium?

Griffith used Streptococcus pneumoniae: heat-killed smooth (virulent) cells mixed with live rough (harmless) cells still killed the mice, hinting that something passed between them.

The patchwork coat of a calico cat comes from the random switching-off of which chromosome?

The X chromosome carries the cat's orange-or-black fur gene, and each cell of a female embryo silences one of its two X's at random, which is why nearly all calico cats are female.

Most sequence-reading proteins bind B-DNA through which structural feature?

The major groove is wider because the two strands' attachment points are not directly opposite; it exposes more base edges, so most sequence-reading proteins bind there.

A 1998 Y-chromosome study pointed to which US president as the likely father of an enslaved woman's child?

Thomas Jefferson's male-line relatives carried the same Y chromosome as a descendant of Eston Hemings, Sally Hemings's youngest son; the Y passes largely unchanged from father to son.

The gene for green fluorescent protein, used to make cells glow, was first taken from which sea creature?

A jellyfish, Aequorea victoria, supplied the glowing tag; hitched to another gene, it lights up wherever that gene is active, work honoured with the 2008 Nobel Prize in Chemistry.

Barbara McClintock won a Nobel Prize for discovering 'jumping genes' while studying which crop?

Maize plants with patchy, variegated colouring led McClintock to genes that move around the chromosomes; her 1983 prize came more than 30 years after the discovery.

Which fruit, sold as the Flavr Savr in 1994, was the first genetically modified food to go on sale in the US?

Tomato: the Flavr Savr had a softening gene switched off so that it could ripen fully and still survive shipping, but mounting costs ended production in 1997.

The first Denisovan was identified in 2010 from DNA extracted from what kind of remains?

A finger bone from a child in Siberia's Denisova Cave yielded the DNA; a few per cent of the DNA of people in Melanesia today comes from these lost relatives.

Svante Pääbo won the 2022 Nobel Prize for reading the DNA of which extinct human relatives?

Neanderthals turned out to have interbred with our ancestors: Pääbo's team found that people of European or Asian descent still carry roughly 1–4% Neanderthal DNA.

Dolly the sheep was cloned from a cell taken from which part of an adult ewe?

The mammary-gland origin is why she was named for Dolly Parton; born 5 July 1996 at the Roslin Institute, she was the first mammal cloned from an adult body cell.

In the acronym CRISPR, what does the 'P' stand for?

The full name is clustered regularly interspaced short palindromic repeats, a bacterial antiviral defence repurposed as molecular scissors.

What are the alternative versions of a single gene, such as those for different blood groups, called?

Alleles come in pairs, one inherited from each parent; when the two differ, one can mask the other, which is how a trait can skip a generation.

Which type of cell division halves the chromosome number to make eggs and sperm?

Meiosis also shuffles the DNA: matching chromosomes swap segments before they separate, one reason two children of the same parents inherit different mixes.

The stop signal UAG is nicknamed 'amber' after a surname meaning amber in which language?

Bernstein is German for amber; the name plays on the surname of Harris Bernstein, a student friend of the discoverers, and the other two stop signals were later named ochre and opal.

George Gamow's RNA Tie Club of 1954 set out to solve what?

The genetic code was the puzzle: each of the club's 20 full members stood for one amino acid, and the notes they passed around included Crick's famous 'adaptor hypothesis'.

What did the billionaire who bought James Watson's Nobel medal in 2014 do with it?

Gave it back: Russian tycoon Alisher Usmanov said Watson deserved to keep the medal, which the scientist had sold after saying his remarks on race had left him an unperson.

What kept Rosalind Franklin from sharing the 1962 DNA Nobel?

Her death from ovarian cancer in 1958, at the age of 37, ruled her out, since the prize is not awarded posthumously; an exhibit of her virus models opened at the Brussels fair the day after she died.

Which secret wartime effort employed Maurice Wilkins before he turned to studying DNA?

The Manhattan Project took Wilkins to Berkeley to separate uranium isotopes for the bomb; after the war he moved from physics into biophysics, which led him to DNA.

In 2022 scientists reported the oldest DNA yet recovered, about two million years old, from sediments in which place?

Greenland's far north yielded DNA from mastodons, hares, geese and poplar trees, showing that a forest once grew there in a much warmer climate.

Which kind of radiation damages DNA chiefly by fusing neighbouring thymine bases into dimers?

Ultraviolet rays in sunlight fuse adjacent thymines into dimers that kink the DNA; people with xeroderma pigmentosum, who cannot repair them, can burn after minutes in the sun.

Which garden plant did Gregor Mendel cross-breed in the 1850s and 1860s to work out the basic rules of heredity?

Peas gave Mendel clear either-or traits such as tall or short stems; his laws were not recognised until three botanists rediscovered them in 1900, 16 years after his death.

In 2017 Harvard scientists used CRISPR to store a short film of which animal in the DNA of living bacteria?

A galloping horse from Eadweard Muybridge's Victorian motion studies, among the first moving pictures ever made, was written frame by frame into the bacteria and then read back out.

The fetal DNA found in pregnant women's blood in 1997 comes mainly from where?

The placenta sheds fragments of DNA that usually match the baby's, so a blood sample from about the tenth week can flag conditions with no needle near the womb; Dennis Lo made the 1997 discovery.

In the film Jurassic Park, gaps in the dinosaur DNA are patched with sequences from which animals?

Frogs supply the missing code, and the shortcut drives the plot. Some frogs can change sex in a single-sex group, so the all-female dinosaurs start breeding.

Which king of England, found under a car park in 2012, was identified by DNA from living relatives?

Richard III was confirmed by mitochondrial DNA shared with two descendants of his sister, Anne of York. He was killed at Bosworth in 1485, and the site of his grave was later lost.

Which 1997 science-fiction film takes its title from the letters that stand for the four DNA bases?

Gattaca is spelled entirely from G, A, T and C. The film was shot as The Eighth Day, a title dropped because a Belgian film had already used it.

Which kitchen vegetable carries about five times more DNA in each cell than a human does?

Onion cells hold about five times as much DNA as ours. Biologists use the mismatch as a reality check on any claim that every stretch of DNA must have a purpose.

A stretch of DNA borrowed from which sea creature lets scientists make living cells glow green?

A jellyfish, Aequorea victoria, is the source of green fluorescent protein. Turning that glow into a research tool earned the 2008 Nobel Prize in Chemistry.

A 1998 DNA study linked which US president's male line to a son of the enslaved Sally Hemings?

Thomas Jefferson's family line matched a descendant of Eston Hemings, Sally's youngest son. The test relied on male-line descendants of the president's paternal uncle.

Identical twins share almost all their DNA, yet which feature formed in the womb still differs?

Fingerprints take shape as each fetus touches different parts of the womb, so even identical twins end up with prints of their own.

DNA comparisons show which ape, alongside the bonobo, is the closest living relative of humans?

The chimpanzee line and the human line parted an estimated 7 to 10 million years ago, a short span in evolutionary terms.

Which hormone became, in 1982, the first medicine made by bacteria carrying a human gene?

Insulin had come from pig and cow pancreases, and eight ounces could take two tons of pig parts. Bacteria carrying the human instructions ended that reliance.

People with roots outside Africa carry a few percent of DNA inherited from which extinct relatives?

Neanderthals interbred with modern humans who had left Africa, and their descendants across Europe, Asia and the Americas still carry roughly 1–4% of that DNA.

Which fruit, sold in 1994 as the Flavr Savr, was the first food with altered DNA licensed for people to eat?

The tomato was redesigned to ripen on the vine without going soft on the long trip to market. It reached shops in 1994 and was gone by 1997.

Golden Rice was given extra DNA so that its yellow grains supply the body with which nutrient?

Vitamin A is made in the body from beta-carotene, the pigment that colours the grains. The rice was developed to help children in regions where diets run short of it.

In 2007, 23andMe became the first company to sell a home genetic test using DNA from which body fluid?

Saliva is about 99% water, but it also carries cells shed from the lining of the mouth, and those hold enough DNA for a full test without a needle.

On average, which of these relatives shares about a quarter of a person's DNA, half as much as a parent?

A grandparent shares about 25%, the same as an aunt, an uncle or a half-sibling. First cousins and great-grandparents sit one step further out.

If the DNA packed inside a single human cell were stretched out end to end, roughly how long would it be?

About 2 metres of DNA fits inside each cell because it is wound tightly around protein spools and folded again and again, into a space about six thousandths of a millimetre across.

Which genealogy DNA test follows the piece handed almost unchanged from father to son down a male line?

Y-DNA sits on the chromosome that only males carry, so one man's result speaks for his whole paternal line. A woman who wants it has to ask a father or brother to test.

Which cat coat, almost always female, comes from cells randomly shutting down one copy of their X-linked DNA?

Calico patches show which X each patch of skin kept working: one carries orange fur, the other black. A male has a single X, so he can rarely wear both colours.

Which inherited disorder stems from a single swapped DNA letter in the instructions for haemoglobin?

Sickle cell disease has persisted because carrying one copy of the altered instruction gives some protection against malaria.

Whose televised 1995 murder trial in Los Angeles turned on jurors' doubts about then-novel DNA evidence?

O. J. Simpson was acquitted after his lawyers persuaded the jury there was reasonable doubt about the DNA evidence, a science few people then knew how to weigh.

Which British royal gave the DNA sample that helped confirm the remains of Russia's murdered Romanovs?

Prince Philip was a great-nephew of Tsarina Alexandra, so his DNA could be compared with the bones of the empress and her children.

Which British science journal published the short paper in which Watson and Crick revealed DNA's structure?

Nature gave the discovery barely two pages, numbered 737 and 738. The issue was dated 25 April, now marked every year in the United States as National DNA Day.

Besides mitochondria, which plant-cell organelle carries its own DNA, a legacy of its free-living ancestor?

A chloroplast descends from a cyanobacterium that took up life inside another cell, and it has kept a small set of its own instructions ever since.

What name is given to agents, such as X-rays and ultraviolet light, that permanently change DNA?

Mutagens were first demonstrated in 1927, when Hermann Muller showed that X-rays could cause inheritable changes in the insects he bred for his research.

Which term describes alternative versions of one stretch of DNA, such as those behind blood groups A, B and O?

Alleles of the ABO blood-group instruction come in six common variants, and nearly every living person carries some pairing of them.

Which Austrian-born chemist found that DNA's bases occur in matched amounts, a clue that they pair up?

Erwin Chargaff explained his ratios to Watson and Crick in 1952 despite disliking them. After the 1962 Nobel Prize he wrote to scientists worldwide about his exclusion.

Which scientist, later a Nobel Peace Prize winner, published a mistaken three-stranded model of DNA's structure?

Linus Pauling's model treated the phosphate groups as neutral, a basic slip that clashed with DNA being an acid. He later blamed misleading density data.

Where in the British capital was Rosalind Franklin working when she made her famous X-ray images of DNA?

King's College was not a happy posting for Franklin. After disagreements with her director and with Maurice Wilkins, she moved across the city to Birkbeck.

DNA's structure was solved at which Cambridge physics lab, where the electron and neutron were also found?

Cavendish Laboratory was a home for physicists, but Crick worked there in a medical research unit headed by Max Perutz when Watson arrived from the United States.

Meselson and Stahl showed that each copied DNA molecule keeps one old strand, a pattern given what name?

Semiconservative copying was Watson and Crick's own prediction, and the 1958 test that confirmed it has been called the most beautiful experiment in biology.

When DNA is copied, which adjective describes the new strand that must be built backwards in short pieces?

Lagging is the label because this strand points the wrong way for the copying enzyme, so it needs many separate starts while its partner is made in one continuous run.

Which ability lets the DNA-copying enzyme back up and remove a wrongly paired base?

Proofreading lets the enzyme chew back one step and try again. How thoroughly a species does it sets how often errors slip into its DNA.

Which term describes DNA's two strands pointing in opposite directions, forcing one to be copied in pieces?

Antiparallel strands are named by their ends: one runs 5′ to 3′ while its partner runs 3′ to 5′, like the two carriageways of a road.

DNA's smaller, single-ring bases, cytosine among them, belong to which chemical family?

Pyrimidines turn up well beyond DNA: thiamine, the nutrient also called B1, is built around the same six-membered ring.

Which pinched region of a chromosome holds its two copied DNA arms together until the cell divides?

The centromere also gives each chromosome its map references: it separates a short arm, labelled p, from a long arm, labelled q.

Bacteria keep their DNA in which irregular region of the cell, which has no membrane around it?

Nucleoid DNA is folded into a compact, organised bundle, yet it floats free in the cell with nothing walling it off from the machinery that reads it.

Which small chemical tag, attached to DNA's cytosine bases, can switch a gene off without changing its code?

A methyl group placed on a gene's control region typically shuts the gene down. The same tagging helps keep one X silent in female mammals.

Susumu Ohno popularised which label for stretches of DNA that seem to serve no purpose?

Junk DNA entered the vocabulary in the late 1950s, and Ohno's 1972 paper made it famous. Biologists still argue over how much human DNA truly does nothing.

Which inherited brain disorder is caused by the DNA letters CAG repeating too many times in one gene?

Huntington's disease usually shows itself around the age of 40. The extra repeats add a long run of glutamine to one protein, which slowly damages brain cells.

A 2013 US Supreme Court ruling on patenting human DNA centred on which gene linked to breast cancer risk?

BRCA1 was isolated and patented by the testing firm Myriad Genetics. The justices ruled unanimously that naturally occurring DNA cannot be patented merely because someone has isolated it.

Which lab technique sorts DNA fragments by size by pulling them through a porous slab?

Gel electrophoresis works because DNA's phosphate groups carry a negative charge, so every fragment creeps toward the positive end and the small ones travel fastest.

Which scientist's pea-plant experiments revealed the rules of inheritance decades before DNA's role was known?

Gregor Mendel was an Augustinian friar who became a monk partly to get an education he could not pay for. His results went unrecognised until the turn of the 20th century.

In 2018 He Jiankui announced the birth of twin girls whose DNA he had edited as embryos in which country?

China answered with a prosecution: a court gave He three years in prison and a fine of 3 million yuan for illegal medical practice.

Which astronaut spent 340 days in orbit while NASA compared his DNA with that of his identical twin on Earth?

Scott Kelly flew the mission while his brother Mark, an astronaut himself, stayed on the ground as the experiment's control.

Which bacterial protein, steered by a short guide RNA, makes the cut in CRISPR editing of DNA?

Cas9 became a programmable tool in 2012, when two researchers fused its pair of guide RNAs into one, letting laboratories aim it at a chosen sequence.

Which American won a 1983 Nobel Prize for showing, in maize, that pieces of DNA can jump from place to place?

Barbara McClintock met such scepticism that she stopped publishing her data. Decades later she became the first woman to win that prize without sharing it.

Which quantum physicist's book What Is Life? inspired both Watson and Crick before they solved DNA's structure?

Erwin Schrödinger based the book on public lectures he gave in Dublin, where he pictured heredity as stored in an 'aperiodic crystal'.

Which biochemist won a 1910 Nobel Prize for working out the chemical make-up of nucleic acids?

Albrecht Kossel's work between 1885 and 1901 showed which bases nucleic acids are built from. He also discovered histones, the protein spools that DNA wraps around.

Which extinct African animal became, in 1984, the first extinct creature to have its DNA analysed?

The quagga turned out to be a subspecies of the plains zebra, and the 1984 study of it launched the whole field of ancient DNA analysis.

Which bacterium, a cause of childhood meningitis, was the first free-living organism to have all its DNA read?

Haemophilus influenzae was finished in 1995 by Craig Venter's team, who broke its DNA into random pieces and let computers reassemble them, the 'shotgun' method.

Which American biochemist shared a 1959 Nobel Prize after isolating the first enzyme found to assemble DNA?

Arthur Kornberg isolated the enzyme in 1956 and had his Nobel Prize three years later. His son Roger won one too, the 2006 prize in Chemistry.