L’histoire de p et q: Urban Myths of Cytogenetics

Karyotypes are sooooo 20th century. Time was when a ripe crop of G-banded chromosomes promised a fruitful harvest of genetic secrets. But nowadays a Giemsa-stained karyotype seems like a quaint low resolution black and white TV set – those cute little D & G groups even have rabbit-ear antennas – compared with the bright, sexy colors of FISH, the fine oligonucleotide detail of microarrays, and the dense volumes of data of generated by high throughput DNA sequencing.

But before all that trypsin, calf serum, and Giemsa stain sails off in a T-25 culture flask to navigate the seas of our mythic memories, some cytogenetic stories need to be told. The tale I want to relate started with an email from Debbie Collins, one of our Kansas City genetic counseling colleagues.

“I went to a lecture today,” Debbie’s email began, “and learned how the chromosome’s short and long arms came to be called p & q.” She then related a story that was completely different than what I had always held to be true.

Debbie’s email got me into a Rudyard Kipling frame of mind. Just how did the chromosome get its name? As it turns out, probably neither Debbie’s story nor my story is true. I searched for the “real” answer in standard genetics textbooks and PubMed, but to no avail. So I unscientifically queried geneticists and cytogeneticists of various stripes and ages about how they thought “p” & “q” came to be the official chromosomal designations. Here are their stories, with annotations by me:

1)    The French Connection. This was the most popular version in my unofficial survey.  In this story, “p” stands for petite, the French word for “short.” The long arm came to be called “q” because “q” follows “p” in the alphabet. But that seems inconsistent. Why would one chromosomal arm be named after a word and the other arm named after a letter? It would be more logical to call the long arm “g” for grande, French for “big” or “large.”

2)    Francophones vs. Anglophones. In this version, the French in fact wanted to go avec “p” et “g”. Mais l’English speaking contingent objected to the French conquering the entire chromosome, apparently still harboring some nationalistic resentment nine centuries after The Norman Conquest. The Anglophones held out for “q” because, they claimed, “q” follows “p” (see The French Connection above). But really “q” appears English and also had the quality of making “p” evoke English rather than French. Even though it gave the appearance of a civilized linguistic compromise in which both sides got to name half of a chromosome, victoire pour les Anglais. Hastings avenged!

3)    The New York Typesetter’s Error. This is the version Debbie Collins related to me. The 1971 Paris conferees recommended “p” and “g” á la petite et grande. The nomenclature was reported in 1972 in Birth Defects: Original Article Series, which was published in New York City. A mythical typesetter inadvertently confused “g” for “q”.  The mistake was noticed after the issue had gone to press, too late for correction.

Great story, which caters to our stereotypes of New Yorkers’ penchant for giving language a unique twist. Sadly, though, it is not likely true. First off, I’ve never met a cytogeneticist who was not pathologically detail-oriented, and there is no way they would ever let an error like that get beyond the earliest stages. But more tellingly, although the Paris Conference indeed recommended “p” and “q”, these designations were in use at least 5 years before the 1971 meeting.

4)    The Hardy-Weinberg Equilbrium. As one source quoted to me, all geneticists know that p + q = 1. This has nice poetic and historical resonance . But it sounds too pat to be true. Somehow, I can’t imagine a sober-minded committee thinking this up, and then everyone agreeing to it (or perhaps they weren’t sober). Besides, what does cytogenetics have to do with the Hardy-Weinberg Law?

After spending an inordinate amount of time on PubMed, I think that I have narrowed down the start of the p/q story to the Chicago Conference in 1966, also published in Birth Defects: Original Article Series (I have to admit, though, that I have been unable to obtain a copy of this publication. If anybody is willing to send me an electronic or print copy, I would be forever indebted). The 1960 Denver Conference, by the way, makes no reference to “p” & “q.”

Which story do you think is true?  History is essentially the stories about our past that we have come to believe to be true. So let us choose our history systematically and democratically, rather than leaving it to the confabulations of story tellers or the biased views of the powerful. We can create the truth by popular vote, rather than simply relying on bothersome facts. Use the polling box below to vote for your favorite story so we can settle on the official History of Chromosome Nomenclature. Please, no stuffing the ballot box to ensure that your favorite theory wins; I have ways of finding this out and I will hunt you down. It would also be fun to hear other theories that I may have overlooked, so please use the Comments section to add to the list of Urban Legends of Cytogenetics.

See the follow-up to this posting on the DNA Exchange: “p+q = Solved, Being The True Story of How the Chromosome Got Its Name.”

Thanks to Debbie Collins, Alex Minna Stern, and Nathaniel Comfort for helpful discussions.


Filed under Robert Resta

8 responses to “L’histoire de p et q: Urban Myths of Cytogenetics

  1. I learned the story as a conglomeration of stories 1 and 4: Petite for P arm, and Q for long arm because associating P and Q made sense via Hardy Weinberg…

  2. Lisa Freese

    Could we not add the familiar phrase ‘mind your p’s and q’s” to the mix since no one is really sure where that came from either we can just assign them both to the same ignominious origin……

  3. Heidi Beaver

    Bob – love this! I feel like a contestant on NPR’s Wait, Wait, Don’t Tell Me choose the real story segment. Perhaps a new job oppportunity if genetic cousneling disappears!

  4. Larry the Truthteller

    Ah, poor professor Resta. Once again you are completely off the mark regarding the origins of the nomenclature in our fair profession. Allow me to expound upon the TRUE origin of “p and q”.

    Two famous research scientists were sitting at a bar when a duck walks in carrying a purse…wait a minute…wrong story…let me start again.

    Two famous research scientists were sitting at a bar when a BLOND duck walks in carrying a purse and bucket of pecans…no no no…that’s still not right…oh, I remember now…

    Two famous research scientists were sitting in their lab after playing a few rounds of “I’ll give you $10 if you drink what’s in this flask”. One was the famous French researcher Dr. Jean-Luc Picard (whose name was used in some minor TV show as homage to his greatness) and the other was the renowned British scientist Professor Stanthorpe Whistlebottom Qed Jr. (whose name, thankfully, was never used in TV or radio). Dr. Picard had just finished off a small bottle of something that made his teeth glow neon blue when the conversation turned to the recent discovery of chromosomes. Both Dr. Picard and Dr. Qed found these structures to be quite fascinating and, wanting to make an imprint in the scientific world, decided that they would start a committee to name the different parts of these structures (this committee eventually led to the formation of the US Patent Office, but that’s another story for another day). They were rightly upset that the name “chromosome” was already given, as they had planned to call them either “Intracellularsubopticalmicroscopicfuzzythingies” or “Snookis”.

    However, not to be totally put off, they decided that they would go ahead and give names to the two parts of the chromosomes. After much bickering within their committee, they decided to follow in the footsteps of the great scientists before them (like Dr. Down, Dr. Scalpel and Dr. Appendix) and name these things after themselves. As Dr. Picard and Professor Qed were considered the Mutt and Jeff of the scientific world, they opted to name the small arm after Dr. Picard and the long arm after Professor Qed.

    Thus was born the “Picard” arm and the “Qed” arm. As the years passed, people started getting lazy and couldn’t be bothered with writing out the entire name for those arms (OMG, U R 2 lazy! LOL) and the names were shortened to “p” and “q”.

    This is the honest to goodness origin of the names. I know it’s true because I was there when it happened. Really.

  5. Diane Masser-Frye

    Brilliant Robert, as always. But here’s one problem with the “French connection.” I went back and read LeJeune’s 1963 seminal paper on Cri-du-Chat. He consistently calls the p arm “le bras court” (not petit) and in a later paper, he references “le bras long” which would lead us to using c and l for short and long instead of p and q (though q doesn’t make sense anyway)…or maybe c and d using your #1 possibility. Thanks for the fascinating read…let us know if you get to the bottom of it!

  6. Alexis C

    I always thought ‘q’ stood for ‘queue’, as in, the French word for ‘tail’. I have no idea where I got that from, but I’m pretty sure it was taught to me somewhere along the way. Anyway, the short arm, and the long ‘tail’. Makes sense to me!

  7. Frank Grass

    I heard (from a talk by Jean deGrouchy) that “p” is for petite, and they were going to do “l” for the long arm, but found there was confusion with “1’, so they chose “q” only because it came after “p” in the alphabet.

  8. Megan

    I can see p and g sounding too much alike and confusing everyone so compromising on q for many of the aforementioned reasons, Hardy-Weinberg, queue for tail, next letter…

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