This study was conducted to isolate and characterize the major
histocompatibility complex (MHC) class IIA gene from Nile tilapia
and to compare between different genotypes of this gene following
infection with Aeromonas hydrophila. To achieve our goals PCR was
used to isolate MHC IIA gene following extraction of genomic DNA
from fish blood and then single strand conformational polymorphism
(SSCP) was used to genotype resistant and susceptible/diseased fish.
The results showed 12 nucleotides deletion polymorphisms in MHC
IIA with a product size of 267 bp in control and resistant fish and 255
bp in susceptible/diseased fish(Glover KA, et al.2007) .Additionally ,
sequences out of 50 from susceptible/diseased fish showed a nonsynonymous
G23T SNP which interestingly changed the stop codon
to glycin (G) amino acid with subsequent right shift to the open
reading frame (ORF) . This SNP also resulted in three genotype
(TT ,TG ,GG) with frequencies of 0.9,0.07 and 0.03 respectively .
total protein , albumin and globulin as well as in the phagocytic. The
G23T SNP was also associated with the expression level of MHC IIA
in spleen with lowest expression in susceptible/diseased fish carrying
GG genotype to resistant fish (Xu T et al .,2008). Thus , SNP-disease
resistance association analysis revealed that genotypes (GG and TG)
and alleles (G) of the G23T SNP were high risk for infection