ATP-binding cassette (ABC) transporters are involved in the active transportation of various endogenous or exogenous substances. Two ABCG2 gene subfamily members have been identified in birds. A detailed comparative study of the ABCG2 and ABCG2-like genes aid our understanding of their evolutionary history at the molecular level and provide a theoretical reference for studying the specific functions of ABCG2 and ABCG2-like genes in birds. We first identified 77 ABCG2/ABCG2-like gene sequences in the genomes of 41 birds. Further analysis showed that both the nucleic acid and amino acid sequences of ABCG2 and ABCG2-like genes were highly conserved and exhibited high homology in birds. However, significant differences in the N-terminal structure were found between the ABCG2 and ABCG2-like amino acid sequences. A selective pressure analysis showed that the ABCG2 and ABCG2-like genes were affected by purifying selection during the process of bird evolution. We believe that multiple members of the ABCG2 gene subfamily exist on chromosome 4 in the ancestors of birds. Over the long course of evolution, only the ABCG2 gene was retained on chromosome 4 in birds. The ABCG2-like gene on chromosome 6 might have originated from chromosome replication or fusion. The structural differences between the N terminus of ABCG2 protein and those of ABCG2-like proteins might lead to functional differences between the corresponding genes.

中文翻译：

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ATP结合盒亚家族G成员2基因亚家族的分子进化及其在鸟类中的旁系同源物。

ATP结合盒（ABC）转运蛋白参与各种内源性或外源性物质的主动转运。已在鸟类中鉴定出两个ABCG2基因亚家族成员。对ABCG2和ABCG2类基因的详细比较研究有助于我们在分子水平上了解它们的进化历史，并为研究禽类ABCG2和ABCG2类基因的特定功能提供理论参考。我们首先在41只鸟类的基因组中鉴定了77个ABCG2 / ABCG2类基因序列。进一步的分析表明，ABCG2和ABCG2类基因的核酸和氨基酸序列均高度保守，并在禽类中表现出高度同源性。但是，在ABCG2和类ABCG2氨基酸序列之间发现了N端结构的显着差异。选择性压力分析表明，在鸟类进化过程中，纯化选择会影响ABCG2和ABCG2类基因。我们相信，ABCG2基因亚家族的多个成员存在于鸟类祖先的4号染色体上。在长期的进化过程中，只有ABCG2基因保留在鸟类的4号染色体上。6号染色体上的ABCG2样基因可能源自染色体复制或融合。ABCG2蛋白N末端和类ABCG2蛋白的N末端之间的结构差异可能导致相应基因之间的功能差异。在长期的进化过程中，只有ABCG2基因保留在鸟类的4号染色体上。6号染色体上的ABCG2样基因可能源自染色体复制或融合。ABCG2蛋白N末端和类ABCG2蛋白的N末端之间的结构差异可能导致相应基因之间的功能差异。在长期的进化过程中，只有ABCG2基因保留在鸟类的4号染色体上。6号染色体上的ABCG2样基因可能源自染色体复制或融合。ABCG2蛋白N末端和类ABCG2蛋白的N末端之间的结构差异可能导致相应基因之间的功能差异。