# 核苷酸多樣性

Nei和Li在1979年引入了一種計算核苷酸多樣性的方法：在從某一種群中取得的多個樣品DNA上隨機取一段序列，將在這些序列上的同一位點鹼基的不同取平均值，即可得核苷酸多樣性的值。他們將這個值記爲「π」。

${\displaystyle \pi =\sum _{ij}x_{i}x_{j}\pi _{ij}=2*\sum _{i=1}^{n}\sum _{j=1}^{i-1}x_{i}x_{j}\pi _{ij}}$

xixj分別代表第i個和第j個序列的對應頻率[註 1]πij則爲兩個序列之間不同位點所佔百分比[註 2]。n則爲總樣本數。

## 註釋

1. ^ 比如一共擁有5個樣本，那麼xixj均爲1/5
2. ^ 舉個例子來說，假設第i個樣本的序列爲ATTAC，第j個樣本的序列爲ATTAT。進行比較可知，兩個序列的長度均爲5個鹼基對，其中有一對鹼基對在兩個樣本間是不同的，πij爲1/5

## 參考

1. ^ Nei, M.; Masatoshi Nei; Wen-Hsiung Li. Mathematical Model for Studying Genetic Variation in Terms of Restriction Endonucleases. PNAS. October 1, 1979, 76 (10): 5269–73. PMC 413122. PMID 291943. doi:10.1073/pnas.76.10.5269.
2. ^ Kilian, B; Ozkan H; Walther A; Kohl J; Dagan T; Salamini F; Martin W. Molecular diversity at 18 loci in 321 wild and 92 domesticate lines reveal no reduction of nucleotide diversity during Triticum monococcum (Einkorn) domestication: implications for the origin of agriculture. Molecular Biology and Evolution. December 2007, 24 (12): 2657–68. PMID 17898361. doi:10.1093/molbev/msm192.
3. ^ Yu, N.; Jensen-Seaman MI; Chemnick L; Ryder O; Li WH. Nucleotide diversity in gorillas. Genetics. March 2004, 166 (3): 1375–83. PMC 1470796. PMID 15082556. doi:10.1534/genetics.166.3.1375.
4. ^ Borowsky, Richard L. Estimating nucleotide diversity from random amplified polymorphic DNA and amplified fragment length polymorphism data. Molecular Phylogenetics and Evolution. January 2001, 18 (1): 143–8. PMID 11161751. doi:10.1006/mpev.2000.0865.
5. ^ Innan, Hideki; Ryohei Terauchib Günter Kahlb; Fumio Tajima. A method for estimating nucleotide diversity from AFLP data. Genetics. March 1, 1999, 151 (3): 1157–64. PMC 1460529. PMID 10049931.