Tag Archives: Chicago Conference

p + q = Solved, Being the True Story of How the Chromosome Got Its Name

A few weeks ago I discussed different stories we have come to tell about the origins of the convention of using “p” and “q” to identify the chromosomal short and long arms, respectively (L’histoire de p et q: Urban Legends of Cytogenetics). That posting created quite a bit of discussion, particularly on the Cytogenetics Listserv. Several cytogenetics colleagues forwarded a comment from their listserv that should stand as the definitive story of how p & q became established as official cytogenetic nomenclature.

The True Version was related by someone who was in the room when the decision was made. In my previous post I alluded to the Battle of Hastings. That imagery was apparently not far off from the truth; one conference attendee reported that at times the session seemed like World War 2 1/2. As I had suspected, the 1966 Chicago Conference* was the scene of the crime. The suspects included some important figures in the history of medical genetics: Klaus Patau, Jérôme Lejeune, and Lionel Penrose.

Klaus Patau first described the clinical and cytogenetic basis of trisomy 13 in 1960, along with his wife Eeva Therman (the Finnish cytogeneticist who was sometimes called Mrs. X Chromosome), the great dysmorphologist Dave Smith, and two other authors. Patau originally worked at Germany’s Kaiser Wilhelm Institute and then went on to a long and illustrious career at the University of Wisconsin at Madison.

France’s Jérôme Jean Louis Marie Lejeune is known for his lifelong devotion to the study and care of people with Down syndrome. He was a devout Catholic and a friend and advisor to Pope John Paul II. In 1959, Lejeune, along with Raymond Turpin and Marthe Gautier, were the first to report the underlying cytogenetics of Down syndrome. Gautier, a physician who worked in Turpin’s laboratory at the Centre National de la Recherche Scientifique in Paris, first thought of the idea to karyotype a patient with Down syndrome patient and noted the presence of an extra chromosome in the cells cultured from a skin biopsy.  Lejeune identified the culprit as the twenty-first chromosome. Decades before, several scientists had suggested that Down syndrome might have a cytogenetic basis, including Petrus Waardenburg, Guido Fanconi, and Lionel Penrose, but the technology was not available at the time to test the theory.

Lionel Penrose, the longtime Galton Chair at the Galton Laboratory at University College London, was one of those great polymaths that England seems to be a breeding ground for. He was a psychiatrist, chess master, mathematician, medical geneticist, and, among other things, proposed a method (now called Penrose’s Law) for fairly allocating votes among countries in international organizations like the UN. He statistically established the association between advancing maternal age and an increased risk of Down syndrome.

Back in Chicago, the nomenclature session lasted many hours. Initially, “s” and “l” were recommended for the chromosomal short and long arms. Patau countered with “k” for kurz (German for “short”). Lejeune strongly argued for “p” for petite. This was followed by arguments about naming the long arm, with the concern that “l” could easily be confused for the number 1. In the wee hours of the morning, Penrose entered the room, wanting to know why the session had not yet ended. After hearing about the difficulties, he offered p & q because they were linguistically neutral, and because p + q = 1, evoking the idea that a short arm and a long arm together make one whole unit.

So it turns out that the True Story is closest to Version 4, what I labeled The Hardy-Weinberg version in my earlier post, but it also contains elements of Version 1 (The French Connection) and Version 2 (Francophones vs. Anglophones). Alas and alack, Version 3 (The NY Typesetter’s Error) appears to have no basis in truth, though it is still a good story. Interestingly, the results of the Voting Poll in my previous posting indicated that most people thought The French Connection was the correct story (garnering about 62% of the 211 votes cast by April 30th), whereas the Hardy-Weinberg story came in a distant third at about 11%, with The Francophones vs. The Anglophones attracting 19%, and the New York Typesetter’s Error coming in last with about 8% of the vote.

I guess that when it comes to history, there’s no such thing as The Truth, only distorted versions of it that over time become mistaken for the real thing. Of course, what is really interesting about history is not The Truth so much as the fact that we need to tell stories about our past, and those stories reflect complex personal, psychological, educational, and sociological factors.

* – Chicago Conference (1966): Standardization in Human Cytogenetics: Birth Defects. Original Article Series, Vol 2, No 2, New York, The National Foundation (1966).

Thank you to my colleagues from the Cytogenetics Listserv for forwarding the communication, and to the many readers of the DNA Exchange who took the time vote on The True Story and share their own stories.


Filed under Robert Resta

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