秈稉稻雜交BC1F1與F2族群之不平衡分離

Abstract

不平衡分離是指雜交後代族群的對偶基因或基因型頻度偏離孟德爾定率的一種現象，造成不平衡分離的原因眾多且複雜，可將不平衡分離發生的類型分成配子型與合子型。 為了解不平衡分離的現象，建立以台中秈10號 (TCS10) 與台稉2號 (TK2) 為親本之F2與4個正反回交 (BC1F1) 族群，以卡方適合度檢定回交族群分子標誌的分離比，再以EM演算法 (expectation and maximum algorithm) 計算不平衡分離的位置與效應的最大概度估計值。實驗結果發現存在配子型的不平衡分離基因座 (segregation distortion loci, SDL)，在F1作為父本的回交族群中 (TCS10/F1、TK2/F1)，定位到第3條染色體的RD0306 – RD0307與第6條染色體的RD0612，這兩個SDL存活力皆接近於0；在F1作為母本的回交族群中 (F1/TCS10、F1/TK2)，定位到第6條染色體RD0603 – RD0605，SDL在F1/TCS10與F1/TK2回交族群中的存活力分別為0.69與0.46。此外，在以F1為雌親的回交族群 (F1/TCS10) 中，第11條染色體的RD1101-RD1102間也定位到一個SDL，SDL存活力為0.59。定位到的4個SDL皆偏向秈型對偶基因。然而，4個回交族群中並無發現有合子的效應發生。F2族群基因型頻度的表現也符合受到配子型不平衡基因影響的結果。 另一方面，為了解不平衡分離是否會對連鎖距離及QTL (quantitative trait locus) 的偵測造成影響，及EM演算法的準確度，本實驗也利用模擬族群的方式來檢驗。透過模擬族群的結果顯示，在一條染色體中存在有1個SDL或2個SDL獨立在不同染色體中時並不影響連鎖距離，也不會影響QTL的偵測或EM演算法的準確度。只有在同一條染色體中存在有2個SDL時會對連鎖圖譜造成影響，2個SDL作用方向相同時會造成連鎖距離的縮短；相反的，2個SDL作用方向相反時會造成連鎖距離的增加。

Segregation distortion is the deviation of the segregation ratio of a locus from the expected Mendelian ratio. Ｍany causes will lead to segregation distortion, and they could be classified into gametic effect and zygotic effect. In order to understand this phenomenon, a F2 and four reciprocal backcross populations from a cross between Taichung Sen 10 (indica) and Taikeng 2 (japonica) rice were created. Chi-square goodness-of-fit tests were used to determine whether the segregation ratios of backcross populations were deviated from expection. The EM algorithm was employed to obtain the maximum likelihood estimators of different populations. The results show that there are SDL of gametic effect in the backcross, but they have different effects on different mating types. When F1 was served as paternal parent in the backcross populations (TCS10/F1、TK2/F1), SDL were detected on the interval between RD0306 and RD0307 of chromosome 3 and RD0612 of chromosome 6. Both of the viabilities of SDL were nearly 0. When F1 was used as maternal parent in the backcross populations (F1/TCS10、F1/TK2), SDL was detected on the interval between RD0603 and RD0605 of chromosome 6. The viabilities of SDL was 0.69 in F1/TCS10 population, and 0.46 in F1/TK2 population. Additional SDL was detected on the interval between RD1101 and RD1102 of chromosome 11 in the backcross population from a cross between F1 and TCS10. The viability of this SDL was 0.59.The four SDL both deviated toward indica allele. However, no zygotic effect in four backcross populations was found. The genotypic frequencies of F2 appeared to be a combination of gametic effects without additional zygotic effect. In the meanwhile, to understand how SDL affect the genetic distance、QTL detection and the accuracy of EM algorithm, simulation experiments were carried out. According to the simulation result, the genetic distance、QTL detection and the accuracy of EM algorithm will not affect by either one SDL nor two SDL on different chromosomes.The only way that the genetic distance is affected by two SDL on the same chromosome. While the effect of two SDL are the same, the genetic distance will reduce. Otherwise, the genetic distance will increase by the two SDL with different direction.