我國(guó)老百姓飯桌上常見(jiàn)的長(zhǎng)豇豆可具有長(zhǎng)達(dá)1米的長(zhǎng)莢,。然而在非洲,，長(zhǎng)豇豆的洋兄弟─普通豇豆的豆莢卻只有人的手指般長(zhǎng)短,。是什么原因?qū)е逻@種“兩兄弟，大不同”的現(xiàn)象出現(xiàn)呢,？
近日,，英國(guó)《自然》出版集團(tuán)旗下著名遺傳學(xué)期刊《遺傳》（Heredity）發(fā)表了我國(guó)科學(xué)家對(duì)長(zhǎng)豇豆育種馴化的最新研究成果，認(rèn)為亞洲人對(duì)豇豆三條特定染色體的持續(xù)人工選擇是導(dǎo)致長(zhǎng)豇豆超長(zhǎng)豆莢形成的遺傳主因,。
浙江省農(nóng)業(yè)科學(xué)院蔬菜所李國(guó)景研究員率領(lǐng)的團(tuán)隊(duì)在國(guó)家,、浙江省自然科學(xué)基金和中美合作項(xiàng)目的資助下，利用1127個(gè)單核苷酸多態(tài)性（一種DNA變異）標(biāo)記分析了我國(guó)95份長(zhǎng)豇豆資源以及4份來(lái)自美國(guó)和非洲的普通豇豆DNA。通過(guò)以“全基因組連鎖不平衡（LD）分析”為主的遺傳學(xué)方法結(jié)合日本學(xué)者提出的“LD變異組分分解”,，研究人員確定長(zhǎng)豇豆和普通豇豆“本是同根生”,，并推測(cè)出其兄弟當(dāng)年“分道揚(yáng)鑣”的可能圖景：最初豇豆的老祖宗生活在非洲，并且將種子供給當(dāng)?shù)厝嗣褡鳛榈鞍踪|(zhì)的主要來(lái)源,。后來(lái)一小部分豇豆隨人口流動(dòng)遷移到了亞洲,，但亞洲人并不喜歡吃它的豆子，卻喜歡食用其嫩莢,。于是人們一代代地選留那些莢長(zhǎng)最長(zhǎng)的豇豆種子進(jìn)行繁殖,，并且讓它們彼此雜交并繼續(xù)選擇。千百年來(lái),，人們?cè)诓恢挥X(jué)中對(duì)豇豆第5,，7和11號(hào)染色體進(jìn)行了高強(qiáng)度的定向選擇，而控制豇豆莢長(zhǎng)的基因正位于這些染色體上,。最終,，在亞洲形成了擁有可長(zhǎng)達(dá)1米超級(jí)豆莢的豇豆新亞種—長(zhǎng)豇豆亞種。該研究還首次提出在遺傳上將長(zhǎng)豇豆劃分為“典型菜用型”和“非典型菜用型”兩大類群,，因?yàn)?ldquo;它們存在著明顯的遺傳‘群體結(jié)構(gòu)’”,，論文第一作者徐沛副研究員解釋說(shuō)。
“可以說(shuō),，雙重‘建立者效應(yīng)’（founder effect）+ 對(duì)特定染色體的高強(qiáng)度持續(xù)選擇是長(zhǎng)豇豆育種馴化過(guò)程中最顯著的特點(diǎn),。這一過(guò)程反映的并不是 ‘進(jìn)化’，而是強(qiáng)調(diào)了外部力量（人為選擇）對(duì)生物多樣性的影響”,，徐沛博士最后總結(jié)說(shuō),。（生物谷Bioon.com）
doi: 10.1038/hdy.2012.8
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Genome wide linkage disequilibrium in Chinese asparagus bean (Vigna. unguiculata ssp. sesquipedialis) germplasm: implications for domestication history and genome wide association studies
P Xu, X Wu, B Wang, J Luo, Y Liu, J D Ehlers, T J Close, P A Roberts, Z Lu, S Wang and G Li
Association mapping of important traits of crop plants relies on first understanding the extent and patterns of linkage disequilibrium (LD) in the particular germplasm being investigated. We characterize here the genetic diversity, population structure and genome wide LD patterns in a set of asparagus bean (Vigna. unguiculata ssp. sesquipedialis) germplasm from China. A diverse collection of 99 asparagus bean and normal cowpea accessions were genotyped with 1127 expressed sequence tag-derived single nucleotide polymorphism markers (SNPs). The proportion of polymorphic SNPs across the collection was relatively low (39%), with an average number of SNPs per locus of 1.33. Bayesian population structure analysis indicated two subdivisions within the collection sampled that generally represented the ‘standard vegetable’ type (subgroup SV) and the ‘non-standard vegetable’ type (subgroup NSV), respectively. Level of LD (r2) was higher and extent of LD persisted longer in subgroup SV than in subgroup NSV, whereas LD decayed rapidly (0–2?cM) in both subgroups. LD decay distance varied among chromosomes, with the longest (≈5?cM) five times longer than the shortest (≈1?cM). Partitioning of LD variance into within- and between-subgroup components coupled with comparative LD decay analysis suggested that linkage group 5, 7 and 10 may have undergone the most intensive epistatic selection toward traits favorable for vegetable use. This work provides a first population genetic insight into domestication history of asparagus bean and demonstrates the feasibility of mapping complex traits by genome wide association study in asparagus bean using a currently available cowpea SNPs marker platform
