Results showed polymorphism in intron 2, but intron 1 and exon 3 were monomorph. On the contrary, Soufy et al. [14
] observed polymorphism for exon 3 in Sanjabi sheep and native Kermanian cattle. Intron 1 was also monomorph, and all samples showed the homozygote genotype. On the other hand, intron 2 was polymorphic and three different genotypes were detected. Three different conformational patterns (AA, AB,
) were determined with frequencies of 73.5, 4, and 22.5%. The allelic frequencies for A
were as 75.5 and 24.5%, respectively. Similar result was observed in Iranian Baluchi sheep [16
]. This inconsistency may be ascribed to breed differences, population and sampling size, environmental factors, mating strategies, geographical position effect, and frequency distribution of genetic variants.
Statistical analysis showed that myostatin locus had no significant effect on YW
> 0.05). Similar to these findings, Masoudi et al. [17
] did not report any significant effect of this locus on YW
. Although, they found significant effect of different genotypes on birth weight, they also did not observe any significant effect on weaning and six month weights. Ansary et al. [16
] detected significant effect of different genotypes on daily gain from birth to 3 month of age (P
< 0.01). This may be due to the environmental effects that exist and affect this trait. It must be pointed that mutation in intron region is classified as a silent mutation and in spite of existence of mutation in this gene any associations is not reported. However, there are reports of diseases caused by silent mutations. It also seems that introns have a role in the expression of gene and necessitate for physical instructors of DNA. But they do not have a major role in rank of amino acids and proteins' instructor [18
In this population, this locus did not show Hardy-Weinberg equilibrium. This confirmed that factors leading to disequilibrium, especially selection, may affect the genetic structure of the population. Based on our results, the investigated population showed a low degree of genotypic variability for the MSTN gene. This may be explained by the conservation and breeding strategies, which have been carried out. In recent years, in this station, only a few rams have been used as sires in breeding plans. Due to small effective population size, inbreeding was high, and, as a consequence, heterozygosity and genetic variability were low. Controlled breeding might help in lowering inbreeding. In spite of low variability for genomic DNA, these data provide evidence that Iranian's Zel sheep breed have a polymorphism in intron 2 for myostatin locus. However, results showed that this locus in this population may not be useful for developing future selection programs, especially marker-assistant selection for improving weight gain and meat traits.
It can be concluded that, although MSTN polymorphism did not have effect on YW, further analysis needs to be conducted on the effect of MSTN genotypes on yearling weight and other body weights. Furthermore, results showed that PCR-RFLP and PCR-SSCP are appropriate tools for evaluating genetic variability.