Molecular Plant Breeding 2024, Vol.15, No.1, 1-7 http://genbreedpublisher.com/index.php/mpb 4 3.2 The main factors to reveal genetic differentiation Many complex factors are involved in genetic differentiation of cypress populations. Chloroplast genome plays a key role in this process, and its sequence variation can provide important clues about genetic differentiation among cypress populations. One of the main factors of genetic differentiation is geographical isolation. Due to geographical isolation, cypress populations live in different habitats and are affected by environmental conditions, land forms and climate for a long time (Li et al., 2022). This isolation leads to a reduction in genetic communication between different geographic populations, which encourages populations to differentiate at the genetic level, and the greater the degree and duration of geographical isolation, the more pronounced the genetic differentiation between populations is likely to be. Another important factor is ecological adaptation. The adaptability of cypress populations to different habitats may lead to genetic differentiation. Due to different environments, cypress populations may gradually develop adaptive characteristics to different habitats, such as adaptability to temperature, humidity and soil conditions. The formation of these ecological adaptive characteristics may be accompanied by the selection of specific genotypes, thus leading to genetic differentiation among cypress populations. In addition, factors such as population size, migration pattern, natural selection and genetic drift may also affect the genetic differentiation of cypress populations. These factors interweave with each other, affect the genetic structure and diversity of cypress population, and promote the genetic differentiation among different geographic populations. 3.3 The influence of geographical environment on genetic diversity Geographic environment has a profound impact on the genetic diversity of cypress, which involves many aspects, from geomorphic features to climatic diversity, shaping the genetic structure of geographic population of Cypress (Xu et al., 2010). The complexity of geographical environment directly affects the genetic differentiation among different populations of cypress. The variation of terrain and geographical isolation resulted in the uneven distribution of cypress population in space. The presence of mountains, rivers, and different land forms can limit gene flow between cypress populations and contribute to genetic differences between populations. This geographical isolation of spatial distribution can lead to reduced gene exchange within geographic populations, thus promoting the occurrence of genetic differentiation. The change of climate conditions also affected the genetic diversity of cypress populations. The climate differences in different geographical environments will trigger the adaptability of cypress populations to different environments, and this adaptability may be reflected at the genetic level. For example, differences in climate factors such as temperature and precipitation may lead to gradual variation in the physiological and morphological characteristics of different populations, thus shaping the genetic characteristics of populations. The stability and change of geographical environment also have significant influence on genetic diversity. The relatively stable geographical environment may maintain the stability of some genetic characteristics, while the changing environmental conditions may promote the gradual variation and selection of some genotypes or phenotypes, thus affecting the genetic diversity of cypress populations. 4 Mechanisms of Genetic Differentiation Revealed by Chloroplast Genome 4.1 The role of chloroplast genome in genetic evolution Chloroplast genome plays a key role in plant genetic evolution, which goes far beyond the mere transmission of genetic information. As an important genetic element in plant cells, chloroplast genome is not only responsible for carrying and transmitting genetic information, but also plays an important functional and adaptive role in the evolution of populations (Jia et al., 2019, Bulletin of Biology, 44(11): 7-9).
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