中文摘要：

文章利用生物信息学方法对太平洋牡蛎（Crassostrea gigas Thunberg）酪氨酸酶基因家族的氨基酸序列特征、分类及系统发生进行了分析。结果表明，太平洋牡蛎酪氨酸酶基因家族在进化过程中存在基因扩张现象，其主要方式是基因重复。太平洋牡蛎酪氨酸酶可分为3种类型：分泌型（TypeA），胞内型（TypeB）和具跨膜结构域型（Typec）。根据太平洋牡蛎酪氨酸酶进化树分析，发现TypeA酪氨酸酶中，tyrl8与其他TypeA酪氨酸酶分化较大，可能是较早分化出来的酪氨酸酶；TypeB酪氨酸中的tyr2和tyr9以及TypeC中的tyr8为较早分化出的酪氨酸酶。系统发生树分析发现太平洋牡蛎酪氨酸酶的聚类受酪氨酸酶类型以及基因位置的影响，其分泌型酪氨酸酶首先与头足类分泌型酪氨酸酶聚在一起，然后与线形动物门分泌型酪氨酸酶聚在一起，与腔肠动物门分泌型酪氨酸酶分化明显。太平洋牡蛎胞内型酪氨酸酶自身分化较大，总体上与线性动物门、其他软体动物胞内型酪氨酸酶聚为一支，与扁形动物门、脊索动物门、腔肠动物门胞内型酪氨酸酶分化较大。太平洋牡蛎具跨膜结构域型酪氨酸酶与扁形动物门、环形动物门以及脊索动物门具跨膜结构域型酪氨酸酶分化明显，与合浦珠母贝具跨膜结构域型酪氨酸酶聚为一支。这表明双壳类的TypeC型酪氨酸酶与其他物种的同源酶的进化差异较大。文章首次探讨了太平洋牡蛎酪氨酸酶家族分类、分化及系统发生，以期对太平洋牡蛎酪氨酸酶基因家族的理论研究和实际应用提供依据。

英文摘要：

The deduced amino acid sequence characteristics, classification and phylogeny of tyrosinase gene family in the Pacific oyster （Crassostrea gigas Thunberg） were analyzed using bioinformatics methods. The results showed that gene duplication was the major cause of tyrosinase gene expansion in the Pacific oyster. The tyrosinase gene family in the Pacific oyster can be further classified into three types： secreted form （Type A）, cytosolic form （Type B） and membrane-bound form（Type C）. Based on the topology of the phylogenetic tree of the Pacific oyster tyrosinases, among Type A isoforms, tyrl8 seemed divergent from other Type A tyrosinases early, while tyr2 and tyr9 appeared divergent early in Type B. In Type C tyrosinses, tyr8 was divergent early. The cluster of the Pacific oyster tyrosinasesis determined by their classifications and positions in the scaffolds. Further analysis suggested that Type A tyrosinases of C. gigas clustered with those from cephalo- pods and then with nematodes and cnidarians. Type B tyrosinases were generally clustered with the same type oftyrosinases from molluscas and nematodes, and then with those from platyhelminths, cnidarians and chordates. Type A tyrosinases in the Pacific oyster and the Pearl oyster expanded independently and were divergent from membrane-bound form of tyrosinases in chordata, platyhelminthes and annelida. These observations suggested that Type C tyrosinases in the bivalve had a distinct evolution direction.