| Summary: | 碩士 === 國立成功大學 === 生物學系碩博士班 === 93 === Rice, one of the most important crops, provide a half of world populations with a staple food. In plants, hemoglobin genes have long been considered to exist only in nitrogen-fixing nodules. Non-symbiotic hemoglobins that express in nonnodulating species were extensively found in lower and higher plants. This study examined the genetic diversity at non-symbiotic hemoglobin paralogs, which are all located on the third chromosome of Oryza. Tajima’s D values were estimated from noncoding and coding regions, as well as from nonsynonymous and synonymous substitution sites for examing modes of natural selection. Significicant negative Tajima’s D valus are detected in the four members of RHB gene family of wild rice due to excessive low-frequency polymorphisms among nucleotide sequences. The phenomenon prevails in most genes of wild rice, common effects of recent demographic expansion. HKA statistics suggests that all RHB paralogs are shaped by negative selection. Based on the dN/dS ratio and sliding window analysis also confirm the above selection mode of RHB gene family in Oryza.
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