Maize Genomics and Genetics 2024, Vol.15, No.1, 27-35 http://cropscipublisher.com/index.php/mgg 31 Subsequent studies employed DNA-based markers, such as RFLPs, SSRs, and SNPs, to further resolve phylogenetic relationships. The integration of these molecular markers with isoenzymatic data has provided a more comprehensive understanding of the evolutionary history and genetic diversity within Zea. 3.3 Key phylogenetic markers and their relevance Isoenzymatic markers have played a crucial role in delineating phylogenetic relationships within Zea. Isoenzymes are advantageous because they are relatively easy to assay and provide a direct measure of genetic variation at the protein level. Early studies using isoenzymes, Doebley et al. (1984) study, identified significant genetic differentiation between maize and teosinte species, supporting the hypothesis of multiple domestication events and subsequent gene flow between wild and cultivated populations. Beyond isoenzymes, several other phylogenetic markers have been pivotal in studying Zea's evolutionary relationships. Chloroplast DNA (cpDNA) markers have provided valuable information on maternal lineage and biogeographical patterns. cpDNA studies have confirmed the monophyletic origin of maize and its closest relationship to Zea mays ssp. parviglumis, while also highlighting the role of Zea mays ssp. mexicana in contributing to genetic diversity through hybridization (Sánchez et al., 1999). Nuclear DNA markers, including SSRs and SNPs, have enabled high-resolution analyses of genetic diversity and population structure. SSR markers, with their high polymorphism and co-dominant inheritance, have been extensively used to study the genetic relationships and diversity within Zea. These markers have helped identify distinct genetic clusters corresponding to different teosinte species and maize landraces, illustrating the complex patterns of domestication and gene flow (Matsuoka et al., 2002). SNP markers, identified through NGS technologies, have revolutionized phylogenetic studies by providing dense genetic maps and facilitating genome-wide association studies (GWAS). SNP analyses have corroborated earlier findings of maize's closest relationship to Zea mays ssp. parviglumis and have identified numerous genomic regions associated with domestication traits. These studies have highlighted the role of both selective sweeps and introgression in shaping the genetic architecture of maize (Van Heerwaarden et al., 2011). In addition to molecular markers, morphological and ecological data continue to contribute to understanding phylogenetic relationships within Zea. Traits such as plant architecture, kernel morphology, and flowering time provide complementary information that, when integrated with molecular data, enhances the resolution of phylogenetic analyses. 4 Findings from Isoenzymatic Studies 4.1 Summary of key studies on isoenzymatic variation inZea Isoenzymatic studies have provided significant insights into the phylogenetic relationships within the genus Zea. These studies utilize isoenzymes as markers to assess genetic diversity and evolutionary relationships among species and subspecies. One of the seminal works in this field was conducted by Doebley et al. (1984), who analyzed isoenzymatic variation across multiple Zea species. They utilized starch gel electrophoresis to separate and identify different isoenzymes, revealing considerable genetic differentiation between maize (Zea mays ssp. mays) and its wild relatives, the teosintes (Doebley et al., 1984). Another key study by Goodman and Stuber (1983) focused on the isoenzymatic variation within maize and teosinte populations. Their work highlighted the extensive genetic diversity present within teosinte populations and underscored the close genetic relationship between maize and Zea mays ssp. parviglumis. This study was instrumental in establishing the hypothesis that Zea mays ssp. parviglumis is the most likely progenitor of domesticated maize. Subsequent studies have built on these foundational works, employing more sophisticated techniques to analyze isoenzymatic variation. For instance, studies by Sánchez et al. (1999) and Matsuoka et al. (2002) have used isoenzymatic data in conjunction with other molecular markers to provide a more comprehensive understanding of
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