I’m blogging about the human genome this month in conjunction with my new book on genetics, The Violinist’s Thumb. This series will cover strange cancers, DNA palindromes and semordnilaps, interspecies hanky-panky, and the near extinction of humankind. But I thought I’d start off with something basic—with names, the first step in getting to know somebody.
We’ll be getting to know each human chromosome and its personality over the next few weeks, as I’ll extract a story from one or two chromosomes for each post. Chromosomes are discrete bundles of DNA inside the cell nucleus, and they house our genes. But despite the importance of chromosomes to our basic essence—they’re one fundamental thing all humans share—geneticists sure didn’t expend much energy thinking up names for them. They were in fact named with all the creativity of shoe sizes. Chromosome 1 is the longest, chromosome 2 the second-longest, chromosome 3 (spoiler alert!) the third-longest, and so on.
The only break in the monotony comes with chromosome 21. You’d think this would be the 21st-longest, but no—it’s the 22nd-longest, and the shortest chromosome overall, roughly 3 million DNA bases shorter than chromosome 22. Back when scientists started cataloging human chromosomes, they had much poorer microscopes, and a difference of even many millions wasn’t easy to measure. That’s because chromosomes in living cells usually look like unraveled skeins of yarn, not the neat, plump, paper-doll pairs we’re used to seeing on karyotypes (like the snazzy one below). During this era, scientists mistakenly measured chromosome 21 as longer, and by the time they realized this, it had already become infamous as the cause of Down syndrome. (Down syndrome occurs when someone has three copies of chromosome 21 instead of the normal two.) Rather than risk confusion, scientists let the misnomer “21” stick.
Compared to chromosomes, gene names have more pep. Genes are units of inheritance that control body traits and get passed from generation to generation; they’re made of DNA, and cells “read” genes like blueprints to make things such as proteins. Because there are so many more genes than chromosomes—each chromosome contains between a few hundred and a few thousand genes—scientists have had more latitude to indulge their creativity. For reasons of tradition and one-upmanship, fruit fly geneticists have emerged as the wits and wags of genetic nomenclature. Different fruit fly genes are called groucho, smurf, lost in space, fear of intimacy, tiggywinkle, and the Dada-esque faint sausage. Without the tinman gene, fruit flies cannot grow a heart. The cleopatra gene can kill flies when it interacts with another gene, asp. Cheap date leaves flies tipsy after a mere sip of alcohol. Ken and barbie mutants lack genitalia.
Fruit flies may be the comic kings of genetics, but other animals do have some zingers. A gene that leaves mammals with extras nipples earned the name scaramanga, after the James Bond villain with too many. A gene that removes blood cells from circulation in fish became vlad tepes, after Vlad the Impaler, the supposed inspiration for Dracula. The backronym for the “POK erythroid myeloid ontogenic” gene first characterized in mice—pokemon—nearly provoked a lawsuit, since it contributes to the spread of cancer, and the lawyers at Pokémon Inc. didn’t want their cute little pocket monsters confused with tumors.
In contrast to this whimsy, the names of most genes are ugly, especially when they’re also found in humans—freak acronyms that maybe six people worldwide understand. For example, the full name of the human SEMA5A gene is (take a breath), “Sema domain, seven thrombospondin repeats (type 1 and type 1-like), transmembrane domain (TM) and short cytoplasmic domain, (semaphorin) 5A.” Why are human gene names such killjoys?
Diseases. The ex-pokemon gene—now known as zbtb7—contributes to the spread of cancer in humans, too, which makes it less funny. Worse is sonic hedgehog. A graduate student—a wacky fruit fly guy—discovered it in the 1990s and classified it within a group of genes that, when mutated, cause fly embryos to grow spiky quills. Scientists had already named similar genes after real species like the moonrat and desert hedgehogs. Robert Riddle thought naming his gene after the speedy Sega hero would be funny. By happenstance, sonic proved one of the most important genes in the entire animal repertoire—humans have a copy on chromosome 7—and it’s crucial for embryonic development. Flaws in the gene lead to heart-breaking birth defects, and it’s no fun explaining to some poor mother that sonic hedgehog might kill her child.
All in all, it’s probably best to keep human gene names sterile and technical. Still, that doesn’t mean we have to live with stupefyingly boring chromosome names. I wrote my first book on the periodic table, and got endless delight from learning the eponym behind every element—the gods, cities, myths, and immortal scientists enshrined on the table. Compare the resonance of einsteinium and promethium to chromosome 7 and chromosome 21. So why not give chromosomes a bit more zip, even as nicknames?
Personally, I’d name one chromosome Rosalind, after Rosalind Franklin, who died before she could share a Nobel Prize with Watson and Crick for helping to elucidate the double-helix structure of DNA. (In some ways, a chromosome eponym would be an even bigger honor than a Nobel, since there are far fewer chromosomes than Nobel laureates!) I’d also name chromosome 2 Demos, Greek for people, since (as we’ll see in a later entry) the birth of this chromosome made our arrangement of DNA uniquely human, distinguishing us from chimps and gorillas and other primates. But if anyone wants to refute my choices, or has a favorite scientist, city, or myth of their own to christen a chromosome, feel free to nominate it below …
* * *
Incidentally, you might be wondering: If I’m giving the milk away for free on Slate, why buy the cow? Well, I’m not giving the milk away, or at least not too much. Instead of covering each chromosome one by one, the book takes on broader, more narrative stories about human history—tales many scientists assumed lost forever. So while you’ll get a taste here of the cryptography, cannibalism, foolhardy voyages, illicit sex, and, yes, science, in The Violinist’s Thumb, it’s only a taste. (You can see a table of contents and a sample here.)