The nuclear DNA content of seven mouse laboratory strains has been mea
sured by flow cytometry. The differences observed between strains as w
ell as those between sexes within the strain were all statistically si
gnificant. The highest DNA content (approximately 6.4 pg/female nucleu
s) was found in the Balb/c strain; the lowest (approximately 5.7 pg/ma
le nucleus) in the C3H/he strain. The difference between sexes varied
from 1.6% (in CD-1 mice) to 6.3% (in nude mice). The interest of these
results is twofold. First, the mouse can now be used to study the ada
ptive significance of genome size variation, so far studied only in. p
lants. Second, DNA content analysis can become a quick method for mous
e strain identification. (C) 1997 Wiley-Liss, Inc.