Legume Genomics and Genetics 2025, Vol.16, No.1, 23-32 http://cropscipublisher.com/index.php/lgg 24 variety can vary greatly when grown in different places. This is the competition between genes and the environment. Through years of research, it has been found that understanding these genetic patterns clearly is particularly useful for breeding new varieties that are disease-resistant, drought-resistant and high-yielding (Diers et al., 2018; Hong and Huang, 2024). Of course, the genetic network is extremely complex. Sometimes a single gene can influence several traits, and this is the most troublesome part. This study aims to clarify the genetic pathways behind the important agronomic traits in soybeans. Simply put, I want to understand why genes affect how tall soybeans grow and how many beans they produce. There have been many new discoveries now, such as specific gene markers and candidate genes, as well as complex interaction networks between them. However, it is interesting that the same gene may behave completely differently in different environments-a variety that grows well on this land may not work on another piece of land. So in addition to studying the genes themselves, we also need to consider the impact of the planting environment. Ultimately, conducting these studies is aimed at cultivating better soybean varieties with high yields, strong disease resistance, good adaptability, and the ability to cope with different planting conditions around the world. After all, the global demand for soybeans is increasing, and relying solely on old varieties is definitely not enough. 2 Genetic Basis of Agronomic Traits in Soybean 2.1 Defining agronomic traits When it comes to whether soybeans grow well or not, it actually depends on many aspects. First and foremost, the most intuitive aspect is the yield-which is directly related to the number of pods per plant, the height of the plant, and the weight of a single bean (Hu et al., 2021; Fu et al., 2022; Rani et al., 2023a). However, nowadays the weather is becoming increasingly abnormal, and soybean varieties that can withstand drought conditions are particularly precious (Ouyang et al., 2022; Sun et al., 2022). Pests and diseases are also a headache, often reducing the harvest. Interestingly, the value of soybeans is not only determined by the yield. The protein and oil content in the soybeans is the key to determining the selling price (Zhu et al., 2021). Sometimes, varieties with high yields may not have as good nutritional value. This is quite contradictory. 2.2 Overview of mendelian genetics and quantitative trait loci (QTLs) in soybean When it comes to the genetic characteristics of soybeans, at first, everyone followed Mendel's approach, thinking that a trait was controlled by a single gene. But in actual farming, it is found that those important characteristics of soybeans-such as when they flower, how tall they can grow, and how many beans they produce-are often the result of the combined action of many genes (Hu et al., 2021; Zhu et al., 2021). These complex genetic characteristics are now all referred to as quantitative trait loci (QTLS). Through QTL mapping technology, researchers gradually identified the locations of these characteristics on the genome (Fu et al., 2022). Interestingly, with the emergence of new technologies such as GWAS and SLAF-seq, the localization accuracy has been getting higher and higher, and a number of new key genes have been discovered as a result (Ouyang et al., 2022). However, on the other hand, although many QTLS have been found, when it comes to applying them to breeding, the complex interactions among these genes still need to be considered (Rani et al., 2023a). 2.3 Role of epistasis in complex trait determination When it comes to soybean breeding, the relationships among genes are much more complicated than one might imagine. Different genes can influence each other, and this phenomenon, known as superposition, makes breeding particularly challenging. Look at such seemingly simple features as seed size and shape. In fact, they are the result of multiple genes "fighting" (Figure 1) (Li et al., 2020). What's more troublesome is that some key QTLS can affect several traits simultaneously, which explains why when one trait is improved, other traits will also change (Fu et al., 2022). However, then again, only by understanding these genetic interactions can the genetic potential of soybeans be truly exploited (Diers et al., 2018). Studying the traits of soybeans nowadays is no longer as simple as it was in Mendel's time. From yield to drought resistance, behind each important feature lies a bunch of genes competing. Fortunately, new technologies keep
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