Tag Archives: chromosomes

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