Triticeae Genomics and Genetics, 2024, Vol.15, No.3, 137-151 http://cropscipublisher.com/index.php/tgg 138 order and genetic distances, which are essential for QTL mapping and gene cloning (Hussain et al., 2017; Marcotuli et al., 2017). The main objective of this study is to provide a comprehensive overview of the methods and achievements in high-density genetic mapping of wheat. This includes a detailed discussion of the various genotyping platforms and mapping strategies used for constructing high-density genetic maps, as well as the integration of these maps across different wheat species, highlighting key research and breakthroughs. It will also examine the practical applications of high-density genetic maps in wheat breeding, including marker-assisted selection (MAS) and genomic selection (GS). By synthesizing current knowledge and identifying future research directions, this study aims to emphasize the importance of high-density genetic maps in advancing wheat genetics and breeding, ultimately contributing to global efforts in improving wheat production and resistance. 2 Overview of Genetic Mapping 2.1 Definition and significance Genetic mapping, also known as linkage mapping, is a tool used to depict the genome structure by determining the positions and relative distances of genetic markers on chromosomes. This technique is crucial for understanding the relationship between genes and traits, aiding in the localization of genes or quantitative trait loci (QTL) associated with complex traits (Su et al., 2018; Guo et al., 2020; Ren et al., 2021). High-density genetic maps contain a large number of markers, providing high-resolution data that can precisely identify genomic regions associated with agronomic traits. This not only accelerates marker-assisted selection (MAS) and genomic selection (GS) in breeding programs but also promotes in-depth research into crop genetic diversity and evolutionary history (Guo et al., 2020). 2.2 Historical perspectives 2.2.1 Early genetic maps The concept of genetic mapping dates back to the early 20th century. Thomas Hunt Morgan and his students first established the idea of gene linkage in fruit flies (Drosophila melanogaster), proposing the hypothesis that genes reside on chromosomes (Hegde and Srivastava, 2022). This foundational theory provided the theoretical basis for the subsequent construction of genetic maps. During the 1 950s and 1 960s, as research in plant and animal genetics progressed, researchers began to create rough genetic maps in various organisms. These maps were primarily based on morphological markers and simple sequence repeats (SSRs). These early maps were limited by the number of available markers and their distribution across the genome. Despite these limitations, they provided the theoretical basis for understanding the genetic architecture of complex traits in wheat and other crops (Liu et al., 2018; Gutierrez-Gonzalez et al., 2019). 2.2.2 Evolution of mapping techniques With the advent of molecular biology, genetic mapping techniques underwent significant evolution. The advent of molecular markers, such as single nucleotide polymorphisms (SNPs), revolutionized genetic mapping. High-density SNP arrays, such as the wheat 55 K and wheat 50 K, have enabled the construction of detailed genetic maps with thousands of markers. These maps have been used to identify QTLs for a wide range of traits, including kernel size, weight, and quality traits (Pang et al., 2020; Guo et al., 2020; Ren et al., 2021; Qu et al., 2021). Techniques like genotyping-by-sequencing (GBS) have further enhanced the resolution of genetic maps, allowing for the identification of fine-scale recombination events and structural variations (Gutierrez-Gonzalez et al., 2019; Lv et al., 2021). Recent studies have utilized these high-density maps to explore the genetic control of important traits in wheat. For example, a study using the wheat 55K SNP array identified major QTLs for kernel-related traits, providing insights into the genetic basis of yield components (Ren et al., 2021). Another study constructed a high-density map using the wheat 50K SNP array to map QTLs for plant height and grain traits, highlighting the importance of these maps in breeding programs (Pang et al., 2020). Additionally, consensus maps combining data from multiple populations have been developed to improve genome coverage and marker density, facilitating more accurate QTL mapping and gene discovery (Qu et al., 2021).
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