The relationship between G1 (c.260 G>A) and G4 (c.721 G>A) polymorphisms in the GDF9 gene and the litter size of sheep: A meta-analysis study

Objective: The results of G1 and G4 polymorphisms as litter-size (LS) markers of ewes remain contradictory. The aim was to evaluate the impact of G1 (c.260 G>A) and G4 (c.721 G>A) polymorphisms on the LS of sheep by synthesizing data from multiple previous studies. Methods: Data were extracted from 14 eligible articles. The genotypes of G1 and G4 polymorphisms were homozygous wild-type (WW), heterozygous (WM), and homozygous mutanttype (MM). The standardized mean difference (SMD) method using random effect models was-employed to determine the effect size of G1 and G4 polymorphisms on LS under dominant, recessive, additive, and co-dominant genetic models. Heterogeneity was analyzed with the I2 statistic-index. Publication bias was depicted with funnel plots and tested by Egger’s and Begg’s tests. Results: The study showed that the correlation between G1 polymorphism and LS in sheep was not significant (p > 0.05) under all genetic models. The influence of G4 polymorphism on the LS of sheep was found significantly (p < 0.05) under dominant [SMD = 0.28, I2 = 0% (no heterogeneity)] and co-dominant [SMD = −0.14, I2 = 36% (moderate heterogeneity)] genetic models. The-WM genotype of G4 polymorphism increased LS, while the MM genotype reduced LS in sheep. Publication bias among G1 and G4 polymorphism studies was absent in all genetic models. Conclusion: Thus, the study revealed that G4 polymorphism could be a potential genetic marker for LS in ewes. On the contrary, G1 polymorphism has no association with the LS of ewes.