Animal Molecular Breeding 2024, Vol.14, No.4, 271-279 http://animalscipublisher.com/index.php/amb 273 expression and sequence variations among goat breeds. For instance, the lower plasma concentrations of LH, P4, and E2 in prolific Jintang black goats compared to nonprolific Tibetan goats suggest a genetic basis for their higher fertility rates (Zi et al., 2019). Similarly, the identification of candidate genes and enriched pathways in DBGs provides a genetic framework for understanding their high fertility, as these genes are involved in critical reproductive processes (Zhao et al., 2023). The genetic analysis of Spanish goat breeds further supports the notion that reproductive efficiency, influenced by genetic variation, is a key determinant of fertility (Ziadi et al., 2021; Porto-Neto et al., 2023). In summary, genetic variation among high fertility goat breeds is closely linked to differences in reproductive traits and efficiency. Comparative genomics and genetic diversity assessments provide valuable insights into the genetic mechanisms underlying fertility, which can be leveraged to improve breeding strategies and enhance reproductive performance in goats. 4 Gene Expression Patterns in High Fertility Breeds 4.1 Techniques for measuring gene expression In the study of gene expression patterns in high fertility goat breeds, various advanced techniques are employed. RNA sequencing (RNA-seq) is a prominent method used to measure mRNA and long non-coding RNA (lncRNA) expression levels, providing insights into the molecular mechanisms underlying reproductive traits (Figure 1) (Sun et al., 2022). Single-cell RNA sequencing (scRNA-seq) is another powerful tool that allows for the detailed profiling of gene expression in specific cell types, such as granulosa cells, which are crucial for fertility (Ghafouri et al., 2023). Additionally, quantitative real-time PCR (qPCR) is used to determine the expression profiles of specific genes, such as the PRNT gene, across different tissues (Bi et al., 2021). 4.2 Variability of expression across breeds Gene expression variability across different goat breeds is significant and can be linked to differences in reproductive performance. For instance, in Dazu black goats, transcriptome analysis revealed numerous differentially expressed mRNAs during embryo implantation, highlighting breed-specific gene expression patterns (Zhao et al., 2023). Similarly, in Chuanzhong black goats, whole-genome sequencing identified distinct genetic variations associated with high and low litter sizes, indicating variability in gene expression related to fecundity (Guo et al., 2024). These differences underscore the importance of breed-specific studies to understand the genetic basis of fertility. 4.3 Relationship between gene expression and reproductive performance The relationship between gene expression and reproductive performance is complex and involves multiple pathways and regulatory networks. In high-fertility goats, differentially expressed genes are often enriched in pathways related to reproductive processes, such as the AMPK, PI3K-Akt, and ECM-receptor interaction pathways, which directly or indirectly affect reproduction (Sun et al., 2022). Additionally, genes like DNMT3B and PRNT have been associated with litter size, with specific genetic variants influencing reproductive traits (Hui et al., 2020; Bi et al., 2021). These findings suggest that gene expression patterns are closely linked to reproductive efficiency and can serve as potential markers for breeding programs aimed at enhancing fertility (Tobolski et al., 2021). In summary, the study of gene expression patterns in high fertility goat breeds involves advanced techniques like RNA-seq and scRNA-seq, reveals significant variability across breeds, and highlights the intricate relationship between gene expression and reproductive performance. These insights are crucial for developing strategies to improve fertility in goat breeding programs. 5 Environmental Factors Influencing Gene Expression 5.1 Effects of nutrition on gene activity Nutrition plays a crucial role in regulating gene activity related to embryonic development in goats. The oviduct, which provides nutrition and a location for early embryonic development, is directly involved in the reproductive process. Studies have shown that the expression of mRNAs and long non-coding RNAs (lncRNAs) in the oviduct
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