Hello. I am wondering when the term P0 gained popularity to designate the parental generation. I found examples of the use of P1 in papers from Thomas Hunt Morgan, but I don’t find that convention often anymore, even when researchers are describing an outcross. Is there a convention for using P0 versus P1?
I’d never looked into that, and I can’t answer the question for you - but I pulled a couple of old (and a couple of less-old) textbooks off the shelf, from which I wound up wondering how consistently the parental generation is named at all, let alone the style of its name.
First, I looked at Sturtevant and Beadle’s An Introduction To Genetics, the 1962 edition of a book first published in 1939. F1 and F2 were much in evidence (though never, so far as I could find, defined), but the parental generation wasn’t obviously named, at least so far as I could spot flipping through the book.
Then I looked at Srb, Owen, and Edgar’s General Genetics, the 1965 edition of a book first published in 1952. Again, F1 and F2 were used (and, here, were first defined); in this book, the parental generation is labeled “P” - not P0 or P1, just P.
What surprised me is that when I looked at a relatively modern textbook (Griffiths, Miller, Suzuki, Lewontin, and Gelbart’s An Introduction To Genetic Analysis, copyright 1976 to 1996), they did the same as Srb, Owen, and Edgar, and named the generation “P”. The glossary also defined F1 and F2, but not P, P0, or P1.
A fourth book, Klug and Cummings’s Concepts Of Genetics (copyright 1983-1994) asserts that the parental generation is named P1, in an authoritative voice, though that’s not what I was taught elsewhere.
It seems to me there is rather more confusion here than I would ever have guessed.
I believe that the 0 was added to the P (parental) primarily as an unambiguous indicator of the generation number. It appears to be a back-construction; as Hillel indicated, the initial usage was plain, unadulterated ‘P’. The first F (filial) generation was F1, then F2, etc.
The confusion arises when you consider the F1s as parentals of the F2s. Should they be designated in reference to the relationship (the parents of F2s are P2s) or generation number (1 = 1, whether P or F)? And, if one of the parents in that generation is an outcross (not derived from the initial cross), how should that be indicated? Or, if males from the F1 generation are mated to hermaphrodites/females from the F2? The logic of using the number solely as an indicator of generation rather than relationship becomes clearer (“She’s my sister! She’s my daughter! She’s my sister AND my daughter!”*).
I don’t know when P0 first came into usage. It seems to be most common among worm people, but was not used in the original Brenner Genetics paper. Anybody else care to weigh in?
-Harold
*Props to Faye Dunaway. And to Hillel for consulting the literature rather than relying on faulty memory and random speculation (ahem).