510 
HEMATOLOGY 
systems and others are closed. The most com- 
plex system of this order so far recognized in 
any species is the B system of cattle, undoubt- 
edly followed by its less extensively explored 
homologue, the B system of sheep. Both are 
open systems in spite of the large number of 
blood factors which belong to those systems. 
The blood factors B, G and K which belong to 
the inclusion group BGK are members of the B 
system of cattle and were the starting point" 
of the genetic analysis of that system, which 
presently involves approximately one-half of 
the 80 or so blood factors recognized in cattle 
(Table I) . In the B system, as in other multi-al- 
lelic systems, blood factors segregate as the prop- 
erties of units referred to as phenogroups (e.g., 
the phenogroups I,, Yj, Yo, E'j, I', BI,, 0,1', EM', 
GO,Yo, GY.E',, YiDT, BOiY,D', BGKE'oO', 
. . . etc., through phenogroups of the order 
BGKO2Y, A'B'E',G'KO'Y' in the B system of cat- 
tle). Over 500 phenogroups of the order shown 
have been recognized to date in studies of the B 
system of cattle. They differ markedly in their 
breed distributions. Thus, the phenogroup form- 
ula BGKOoYiA'B'E',G'K'0'Y'/0,TiE',,F'K' is 
typical of Jerseys but is never seen in breeds 
such as Herefords, Angus, Holstein-Friesians 
and so on. Consequently, it is relatively easy for 
the experienced operator to identify the breed 
of cattle from which a blood sample is drawn 
merely by examining the B phenogroups. The 
diploid combinations of the 500+ B pheno- 
groups of cattle give rise to thousands of possi- 
ble blood types and, when all those blood types 
are considered in conjunction with those gener- 
ated by alleles at the remaining 11 loci, the 
overall number of different blood types is far 
greater than the number of cattle that have 
populated this planet.^^ There is also, as indi- 
cated by the figures in Table I, an astounding 
number of possible blood types in pigs. At the 
opposite extreme is the picture in dogs. Ignor- 
ing the difference between Ai and An, and as- 
suming that each of the canine blood factors 
may be inherited independently of one another, 
the number of possible blood types in dogs is 
presently only about 2^ But considering the 
fact that few, if any, laboratories type for the 
high frequency factors F and G, the realized 
variation is much less. 
As might be expected in such complex sys- 
tems as B of cattle, there is occasional recombi- 
nation of the blood factors indicative of cross- 
ing over at the locus or chromosomal region 
which controls the B phenogroups.^" Recently, 
Bouw and Fiorentini^^ have constructed a map 
of the B region of the chromosome. This map, 
based on a study of 57 instructive recombinants 
in 30,000 offspring, indicates some 16 points of 
possible crossing over. Similarly, Baker^^ 
recently constructed a tentative map of the re- 
gion which controls the E system of pigs. Thus, 
for the first time in animals larger than a 
mouse we are beginning to learn something 
about the fine structure of the loci controlling 
blood groups. 
GENE OR CHROMOSOMAL HOMOLOGIES 
It is not, of course, possible to hybridize such 
species as cattle and sheep and, thereby, study 
the segregation of blood factors in F2 hybrids 
or back cross hybrids. Consequently, the only 
indicators of homologous blood group systems 
in the species considered here are cross reacting 
antibodies. Thus, anti-J and anti-sheep 0 of cat- 
tle are excellent antibodies in this context. Not 
only do they define individual differences in the 
J or J-Oc system of cattle^^ but they are also 
effective reagents in defining the R-0 groups of 
sheepi" and the A-0 groups of pigs.^o More- 
over, anti-J of cattle cross reacts with A of 
man,^" thereby establishing homologies be- 
tween the ABO system of man, J of cattle, R-0 
of sheep and A-0 of pigs. The report by Bow- 
dler et al.'' would indicate that the Tr factor of 
dogs also belongs to this system. 
Many of the reagents which define individual 
differences in the B system of cattle also define 
individual differences in the B system of sheep, 
and the converse is also true.''^ Similar homolo- 
gies have been established between the C system 
of cattle and the C system of sheep, and the S 
system of cattle and the M system of sheep. 
When, for example, the red cells of domes- 
tic sheep and other species of the families Bovi- 
dae and Cervidae are injected into rabbits they 
give rise to some antibodies which react specifi- 
cally with the A determinants on cattle red 
cells, thereby indicating that the A system of 
