DNA重复序列的宏观分布趋势

以ＧＣＧ软件和数学模型为工具，用观察到的某ＤＮＡ序列的频数（Ｏ）与理论计算出的此序列频数（Ｔ）的比值（Ｏ／Ｔ）为参数（即相对频数），将基因资料库（包括ＧｅｎＢａｎｋ和ＥＭＢＬＤａｔａＢａｓｅ）的ＤＮＡ序列进行了分析．结果显示ＤＮＡ重复序列的分布存在着如下趋势：（１）越简单的ＤＮＡ重复序列，其相对频数越高，离平衡分布越远；（２）顺向重复序列的分布的相对频数高于反向重复序列的分布；（３）较长的保守序列的相对频数较高；（４）含ＡＴ碱基对的重复序列的相对频数高于含ＧＣ碱基对的重复序列，在较长的ＤＮＡ重复序列中尤其明显：（５）上述ＤＮＡ重复序列分布的趋势存在种属特异性．

The Distribution Trends in Simple Repetitive Stretches of DNA

The five trens of global DNA composition on simple repetitive tretches were revealed by scanning the DNA databases using the GCG program and by analysing the data using a mathematical model.The calculation of the ratio of observed frequency to the theoretical frequency (O/T) allowed different repetitive stretches to be compared with each other on a common ground.It is thus revealed that the global DNA composition is phylogenetically constrained such that the following trends are exist.(Ⅰ)Simplicity is prevailing.The simpler the stretches,the higher the O/T ,that is expressed as (X) a >(XY) a /2 >(XYZ) a /3 >(XWZT) a /4 .(X,Y,W,Z,stands for different base pairs and “ n ”and “ a ” refer to positive round number).(Ⅱ)Tandem stretches are higher in O/T than reverse stretches.It is expressed as (XYXY) n >(XYYX) n. (Ⅲ)Conserved stretches are constrained such that the longer the stretches,the higher the O/T to a certain extent.This is expressed as (XY) a >(XY) a -1 >(XY) a -2 >(XY) a -3 …….(Ⅳ)The stretches containing AT base pairs are higher in O/T than the stretches containing GC base pairs,especially in longer stretches.(Ⅴ)The global DNA composition is organismic specific.The organismic specificity is shown on the different exponential slops of the ln O/T in a macroscopic manner.