and “filial” is not a new word 
https://en.m.wiktionary.org/wiki/filial
They quote gregor mendel ( from here on page 101) who specifically mentions F1’s of impure parents
EDIT: I think the quote was actually from William Castle. I’m not sure why gregor is listed as a coauthor but briefly looking around that doesn’t appear to be true. But still, having the shorthand defined over 110 years ago in a biology textbook is good enough for me 