Animal Molecular Breeding, 2024, Vol.14, No.6, 345-353 http://animalscipublisher.com/index.php/amb 346 precise cuts and subsequent gene editing (Khwatenge and Nahashon, 2021). TALEN and ZFN, while also effective, are more complex and less user-friendly compared to CRISPR/Cas9. TALENs use engineered proteins to bind and cut specific DNA sequences, whereas ZFNs employ zinc finger domains to achieve similar outcomes. Despite their differences, all three technologies have been successfully applied in various organisms, including poultry, to achieve targeted genetic modifications (Figure 1) (Islam et al., 2020). Figure 1 Nuclease-based genome editors (Adopted from Islam et al., 2020) Image caption: (A). Zinc Finger Nuclease (B). Transcription-Activator Like Effector Nuclease (TALEN). (C). Schematic diagram showing genome editing using CRISPR/Cas9 system. The Cas9 induces DNA double-strand break (DSB) which are repaired either by imperfect nonhomologous end-joining (NHEJ) to generate insertion or deletion (indels) or if a repair is provided, by homology-directed repair (HDR) (Adopted from Islam et al., 2020) 2.2 Advantages of gene editing over traditional breeding methods Gene editing technologies offer several advantages over traditional breeding methods. Traditional breeding relies on selective mating and phenotypic selection, which can be time-consuming and less precise. In contrast, gene editing allows for the direct modification of specific genes, leading to faster and more accurate results. For instance, CRISPR/Cas9 has been used to introduce desirable traits in poultry, such as disease resistance and improved production characteristics, which would be challenging to achieve through conventional breeding (Vilela et al., 2020). Additionally, gene editing can overcome the limitations of genetic diversity in breeding populations by introducing new genetic variations that are not present in the existing gene pool. This capability is particularly beneficial in enhancing traits that are difficult to improve through traditional methods, such as resistance to avian diseases and improved feed efficiency. 2.3 Challenges in applying gene editing in poultry Despite its potential, the application of gene editing in poultry breeding faces several challenges. One significant hurdle is the difficulty in accessing and manipulating poultry zygotes, which complicates the gene editing process (Oishi et al., 2016). Additionally, there are technical challenges related to the efficiency and specificity of gene editing tools. For example, off-target effects, where unintended genetic modifications occur, remain a concern with CRISPR/Cas9 technology (Zhang et al., 2019). Furthermore, ethical and regulatory issues surrounding the use of gene editing in animals pose additional challenges. There is ongoing debate about the acceptability and safety of genetically modified organisms (GMOs), which can impact the adoption of these technologies in the poultry industry. Addressing these challenges requires continued research and development to improve the precision and efficiency of gene editing tools, as well as efforts to engage with regulatory bodies and the public to ensure the responsible use of these technologies in poultry breeding.
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