الفهرس 
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Abstract
Two breeds of goats (Zaraiby and Damascus) were used in the present study. The animals were divided in each breed based on prolificacy or litter size to detect the fecundity genes (FecB, FecXI) and Beta casein (CSN2) using Forced PCR restriction fragment length polymorphism (PCR-RFLP) and allele specific PCR (AS-PCR) respectively. Four specific primers were used to detect FecB, FecXI genes and one specific primer includes common forward and two reverse to detect two different alleles of beta casein gene. In view of the Fec B gene located on the same chromosome of beta casein gene (chromosome 6) and the present linkage between them, we tried to detect these alleles and investigate the association between litter size and alleles of beta casein genes. br The results indicated that Zaraiby and Damascus goat either high litter size or low litter size had not point mutation in FecB, FecXI genes. On the other hand, the milk yield in high litter size animal was insignificantly higher than low litter size (.381 and .316) (P ≤ 0.05) with t-test in 2010 and 2011 respectively. So, we studied the beta casein gene that has two different alleles, original A2 (normal) and A1 (mutant -#102;-#114;-#111;-#109; A2) which cause many diseases. The sequence results indicated that the allele A1 is different -#102;-#114;-#111;-#109; A2 allele at codon 67 “C→A or C→G” in Damascus and Zaraiby goats, respectively. We found that ratio of allele A1 in Zaraiby is lower than Damascus (0.54 % and 0.58 % respectively), in addition that the ratio of A1 in twining cases was less than single cases (10%,20%) in Zaraiby and (17.6%, 25%) in Damascus, respectively. this means that milk of Zaraiby is better than Damascus milk.