Page 1038 - Veterinary Immunology, 10th Edition

are found in this system, R and O, coded for by alleles R and r. The
VetBooks.ir production of R and O substances is controlled by a gene called I

and its recessive allele i. If a sheep is homozygous for i, it expresses
neither R nor O antigens. This interaction between the I/i genes and

the R-O system is called an epistatic effect (Fig. 31.3). R and O
antigens are soluble antigens found in the serum of II or Ii sheep
and are passively adsorbed onto red cells. Natural anti-R antibodies
may be found in R-negative sheep. Sheep also fall into two groups

according to whether their red cells have high or low potassium
levels. This is regulated by the EAM blood group system. The Mb
antigen is an inhibitor of potassium transport.

FIG. 31.3 The regulation of expression of EAR blood group
antigens in sheep. The I gene controls expression of the EAR
system.

Serological Testing: Sheep blood groups are detected by hemolytic
tests. One exception to this rule is the EAD system, which is
detected by agglutination.

Pigs

Sixteen pig blood group systems have been identified (EAA to
EAP). Of these, the most important is the EAA system. The EAA

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