水稻是世界上最重要的糧食之一，全世界一半以上的人口，也就是有30億人口以稻米為主食。因為水稻擁有多種特性而成為繼阿拉伯芥後的新模式植物。輸氧蛋白，具有相當重要的生理功能，其廣佈於在自然界的生物中，已經在動物、植物和微生物中皆有發現它的存在。輸氧蛋白廣泛分佈於高等植物，包括單子葉與雙子葉植物。植物中的輸氧蛋白被分為兩群即是：(1) 共生性輸氧蛋白(symbiotic hemoglobin) (2) 非共生性輸氧蛋白(non-symbiotic hemoglobin)，本研究探討野生水稻Oryza rufipogon非共生性輸氧蛋白基因家族所受天擇效應以及演化力量。本研究選用O. rufipogon第3條染色體上的RHB1、RHB2、RHB3和RHB4基因座所組成的基因家族成員，研究結果發現O. rufipogon非共生性輸氧蛋白基因家族皆有過多的低頻率多型性，造成Tajima’s D值負值且顯著的現象，在其它前人的研究具有同樣的現象，推論O. rufipogon族群曾經歷快速擴張結果，因此效應作用在整個基因組中。進一步以noncoding與coding區和非同義及同義置換區域的Tajima’s D值檢測基因是否受天擇作用影響，顯示非共生性輸氧蛋白基因家族中的4個基因在O. rufipogon與O. nivara同源基因中皆受到負向天擇力量，這4個基因在轉譯與氧分子結合區的氨基酸殘基部分都相當保守而沒有變異，顯示非共生性輸氧蛋白基因對O. rufipogon及O. nivara都是重要且具有功能的，因此受到負向天擇力量減少有害的變異產生。

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