F1 hybrids are the first generation of a cross between two
inbred strains. They have many of the useful features of inbred
strains, but also tend to be more vigorous and less sensitive to
adverse environmental conditions. Many characteristics of these F1
hybrid strains (particularly those with a polygenetic mode of
inheritance) will be intermediate between the parental
strains.
F1 hybrid strains should not normally be used for breeding, as
their offspring will show genetic segregation for the loci at which
the parental strains differed. Two individuals of the same F1
hybrid cross will be genetically identical and will accept
reciprocal skin grafts. Such F1 hybrids will also accept grafts of
skin, cells and tumours from either parental strain, though the
converse is not true. The characteristics of F1 hybrids are usually
less well documented than those of inbred strains, although there
are some important exceptions.
Nomenclature of F1 Hybrids is designated by abbreviated capital
letter(s) indicating the parental strains, adding F1 indication and
abbreviated name(s) of breeder(s). The first strain indicated is
the female breeder, while the second strain indicated is the male
breeder. For example: FBNF1/Hsd (BN/RijHsd male * F344/NHsd
female).