- 學位論文
X染色體之連鎖短縱列重複序列對於親緣鑑定能力提升之探討
Study of Linked X-STRs for Improving Forensic Kinship Identification
摘要
X染色體短縱列重覆序列（X-STR）可以加強體染色體短縱列重覆序列（AS-STR）在人身鑑別和親緣鑑定之鑑別能力，近年來逐漸受到重視。在一些特殊情況，像是家族中缺少可進行比對的成員、近親亂倫、大災難時的人身比對，AS-STR可能面臨極限，無法解釋，此時便是X-STR的出場時機，幫助解決這些較複雜的情況。另外當基因發生突變，將導致鑑別力下降，也是常面臨的問題。 本研究選擇一個X-STR基因（locus）—DXS6807，於其上游70萬鹼基對，下游40萬鹼基對距離（physical distance）內，找出適合的十個STR基因進行分析。由於距離相近，所有STR互相連鎖，成為高變異的單倍型（haplotype），可以提供更高的鑑別力。 本研究新建立之十個STR基因，以DXS6807為中心，分別命名為DXS680701、DXS680702、DXS680703、DXS680704、DXS680705、DXS680706、DXS680707、DXS680708、DXS680709、DXS680710。所觀察到之對偶基因(allele)分別有11、27、8、17、7、9、4、8、7與13個，加上DXS6807本身有6個。理論上這十一組搭配會有450億個單倍型組合，但因為連鎖遺傳特性，其組合數量會遠低於此。本研究在130位不具親緣關係的男性身上，共發現129種的單倍型，顯示此組合具高鑑別力。 由彼此無親緣關係之279人（男性136，女性143人），經統計十個新X-STR的多型性指標（polymorphism information content, PIC），範圍介於0.461到0.883，與其他X-STR相比，具有高度變異性，即使單獨使用，也能發揮良好鑑別能力。由於將DXS6807也算在內的11組基因，兩兩配對都具有顯著的連鎖現象（linkage），因此基因型頻率應將11組基因視為一單倍型計算。依此數據顯示，增加連鎖STR基因可明顯提升原有STR基因之鑑別力。 由以上特性得知，同時鑑定新的和原來的STR基因，除了可以提高人別鑑定能力外，在親屬關係上，可以用來判斷當父母和子女的對偶基因型別不相符時，究竟是突變或非親緣所引起的差異。而形成的高變異單倍型，對於親緣關係較遠者，尤其是家族人員基因型資料有缺時，對實際應用判定也有很大的幫助。
並列摘要
X chromosome short tandem repeat (X-STR), which is getting more attention in recent years, can enhance and compensate autosome short tandem repeat (AS-STR). In some special situations, such as deficiency paternity cases (kinship calculation with someone important losing), paternity testing in rape and incest cases, and identification in mass disasters, AS-STR may confront its limitation. When these occur, X-STR and other markers can be strong weapons to solve such tough problems. Besides, allele mutation is another big issue we might have when we analyze STR genotypes, and it will tremendously decrease the power of the method. In our study, we chose DXS6708 as the anchor, and found 10 new STR markers which distributed over upstream 70 hundred thousand base pairs (bp) and downstream 40 hundred thousand bp. Because the distances between each markers are short, they are closely linked, and forming highly variable haplotypes, which have high discriminative power in identification and kinship calculation. Around DXS6807, the ten new STR marker were named: DXS680701, DXS680702, DXS680703, DXS680704, DXS680705, DXS680706, DXS680707, DXS680708, DXS680709, DXS680710. After screening our samples, the amount of alleles of each STR markers are 11, 27, 8, 17, 7, 9, 4, 8, 7, and 13, respectively. We also found 6 alleles in DXS6807, that it has one more allele than the commercial kit originally published. Theoretically, there should be more than 45 billion combinations of haplotypes. Because there are strong linkages between each markers, the amount of haplotype should be far more less the expected. There are 129 types of haplotypes in our 130 unrelated male samples, so these markers, as haplotypes, have high discriminative power in forensic application. The PIC (polymorphism information content) value of the ten X-STR markers ranges from 0.461 to 0.883, which have medium to high variation compared with other common used X-STR marker. The result of LOD score calculation indicated that there are strong linkage between each markers, so they should be looked as a haplotype to count and calculate the appearance frequency. According the haplotype types we observed, increasing the amount of linked STR markers can improve the power of identification and kinship calculation. In conclusion, simultaneously typing the common-used X-STRs and new linked X-STRs, can increase the power of regular identification and kinship calculation. In addition, when there are difference between parents and children, linked X-STR markers can help us differentiate from mutation or having no relationships. Because of high variation of haplotypes, linked X-STR markers can help in special cases such as deficiency paternity cases, paternity testing in rape and incest cases, and identification in mass disasters.
參考文獻
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