Maize Genomics and Genetics 2024, Vol.15, No.2, 70-79 http://cropscipublisher.com/index.php/mgg 72 Figure 1 Locus-based founders contribution to the MM genomes (Adopted from Dell’Acqua et al., 2015) Image caption: Panel a shows that founders’ contribution to MM lines genomes is close to 12.5%, except for CML91, seldom introduced. Because of this, CML91 was excluded from QTL analyses. Some regions still show significant deviation from the expected one-eighth. Regions of Chr 7, 9, and 10 in which founder proportions are distorted are shown in panel (b). Each line depicts the contribution of the founder that is over-represented. Below the line, each tick (colored according to legend in panel (a) indicates a polymorphism between the over-represented and the under-represented founder. The allelic distortion on Chr 7, 10 (for A632 vs. B73), and partially 9 can be related with IBS regions in which the haplotype model cannot distinguish between the two founders (Adopted from Dell’Acqua et al., 2015) 3 Diversity withinZea Species 3.1 Molecular markers and genetic diversity Molecular markers have been extensively used to assess genetic diversity within Zea species. Simple sequence repeat (SSR) markers, for instance, have been employed to investigate the genetic diversity among tropical lowland inbred lines of maize. The study revealed an average of 7.4 alleles per marker, indicating substantial genetic variation within the germplasm (Xia et al., 2004). Another study using SSR markers on CIMMYT maize populations found that most molecular variation was within populations, with significant deviations from Hardy-Weinberg equilibrium due to an excess of homozygosity (Reif et al., 2004). Additionally, nuclear microsatellite loci have been used to examine genetic diversity in wild maize (teosinte), revealing significant genetic structure among populations and variable levels of diversity within subspecies (Gasca-Pineda et al., 2020). 3.2 Geographic distribution of genetic diversity The geographic distribution of genetic diversity in Zea species is influenced by both historical and contemporary factors. For example, the genetic diversity of teosinte has been shaped by past climate fluctuations during the Holocene and Pleistocene, as well as local adaptation and genetic isolation (Gasca-Pineda et al., 2020). In cultivated maize, genetic diversity patterns often reflect the origins and breeding histories of the germplasm. A study on cultivated lentil, which can be paralleled to maize, showed that genetic diversity clusters prominently reflected geographical origins, indicating that similar patterns might be expected in maize (Khazaei et al., 2016). Furthermore, the genetic structure of maize populations adapted to different megaenvironments (tropical, subtropical, and temperate) supports the idea that geographic distribution plays a crucial role in shaping genetic diversity (Reif et al., 2004). 3.3 Factors influencing genetic diversity Several factors influence genetic diversity within Zea species. Local adaptation and historical environmental shifts are significant contributors, as seen in the genetic diversity of teosinte, which is influenced by both contemporary factors and historical climate fluctuations (Gasca-Pineda et al., 2020). The breeding system and colonizing ability also play a role, as demonstrated in a study on wild orchids, where different breeding systems led to varying levels
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