紅檜與台灣扁柏的同功脢遺傳、基因座連鎖與異交率研究

Abstract

使用採自棲蘭山天然林的13株紅檜母樹和8株台灣扁柏母樹之種子，研究兩樹種之同功脢遺傳、基因座連鎖及異交率。分別取其雌配子體（megagametophyte）及胚（embryo），以澱粉膠體電泳技術分析紅檜4種酵素系統8個基因座及台灣扁柏5種酵素系統11個基因座，其中6個基因座具多形性（polymorphism）。電泳所得之結果，利用卡方測驗檢定其雌配子體同功脢帶的分離情形及各多形性基因座間的連鎖關係，並配合胚的電泳結果計算其異交率。 結果發現，紅檜在同一母樹具有2個以上多形性基因座之比例大於台灣扁柏，此與前人研究發現紅檜遺傳變異較台灣扁柏為大的結果相吻合。而紅檜Idh-1, Pgm-1，及Skdh-2基因座，以及台灣扁柏的Mdh-3及Skdh-1基因座的同功脢帶分離比，在部份母樹有偏離孟德爾遺傳定律所預期1:1分離比之情形。亦發現台灣扁柏Mdh-3/Skdh-1兩基因座間有連鎖關係，但紅檜在所分析的基因座間不存在有連鎖關係。另外，紅檜族群之平均多基因座異交率為0.823，而台灣扁柏族群多基因座異交率為0.745，均較一般針葉樹異交率之平均值（0.92）為低，顯示二樹種族群內有相當程度的自交情形存在。同時紅檜族群1之平均單基因座異交率較其多基因座異交率低，則顯示該族群內有近親交配情形存在。

The seeds from 13 trees of Chamaecyparis formosensis and 8 trees of C. obtusa var. formosana collected from natural stands in Chilanshan, Ilan County were used to study the inheritance and linkage relationships of allozymes, and for the estimation of outcrossing rate. Starch gel electrophoresis was employed to asssay the 4 enzyme systems encoded by 8 loci of C. formosensis and the 5 enzyme systems encoded by 11 loci of C. obtusa var. formosana in their megagametophytes and embryos separately. Six of these loci were determined to be polymorphic. The segregation of alleles of each polymorphic loci and linkage relationships of 2-locus combinations among polymorphic loci were tested by chi-square test. The estimation of outcrossing rate was proceeded based on comparison between allozyme variants of the megagametophyte and the embryo in the same seed. The proportion of trees which had more than one heterozygous loci in C. formosensis was found to be greater than C. obtusa var. formosana. This result agrees with that the genetic diversity of C. formosensis is greater than C. obtusa var. formosana porposed by previous researchers. The segregations of allozyme variants show significant deviations from expected 1:1 ratio at Idh-1, Pgm-1, and Skdh-2 loci in some trees of C. formosensis, and Mdh-3 and Skdh-1 loci in some trees of C. obtusa var. formosana. The locus pair of Mdh-3/Skdh-1 was found to be linked in C. obtusa var. formosana. But no linkage relationship was found among the loci analyzed in C. formosensis. In addition, the average multilocus outcrossing rate of populations of C. formosensis is 0.823 and C. obtusa var. formosana is 0.745. These two estimates were lower than the average outcrossing rate of most other conifers (0.92). These results show relatively high selfing rate in the sampled populations. It is inferred that some inbreeding occurred within population 1 of C. formosensis because of the average single-locus outcrossing rate was lower than the multilocus outcrossing rate.