减数分裂重组的分子遗传机制研究进展及在作物育种中的应用

减数分裂是真核生物有性生殖产生染色体数目减半的单倍体配子所必需的生命过程。重组是减数分裂的核心事件之一，既增加了同源染色体间遗传信息的交换，又保证了其在减数分裂后期Ⅰ的正确分离。因此，减数分裂重组不仅增加了后代遗传多样性，还是作物遗传育种的基础。通过提高重组频率或改变其分布可以加速农作物育种进程，而降低或抑制重组可以固定杂种优势。近年来对植物减数分裂重组的分子遗传机制的研究取得了很大进展，包括重组的遗传和表观遗传调控机制，重组的遗传操控技术、固定杂交优势和染色体工程等方面。本文针对以上方面进行了全面的总结，这些内容不仅方便了读者对减数分裂重组的理论认知，还拓展了通过调控减数分裂重组操控生物育种的思路。     

拟南芥减数分裂重组发生的遗传学研究

减数分裂是有性生殖物种世代交替的转折点,而减数分裂过程中发生的遗传重组则是遗传变异的源泉,并为有性生物的进化提供了推动力。现已发现许多基因在重组过程中起重要作用。由于重组蛋白的高度保守性,反向遗传学为研究植物重组蛋白的性质及作用提供了充分的证据。本文就近年来对模式植物拟南芥减数分裂中的DNA双链断裂形成与修复以及同源染色体重组交换等重要事件及其相关基因的功能进行了概述,尤其对ZMM家族蛋白在遗传重组中的作用进行了重点介绍。     

遗传距离

1910年,Morgen TH提出假设:假定沿染色体长度上交换的发生具有同等的几率,那么两个基因位点间的距离可以决定减数分裂过程中发生重组染色体的发生率,即重组分数。重组分数的数值将随     

遗传距离

1910年,Morgen TH提出假设:假定沿染色体长度上交换的发生具有同等的几率,那么两个基因位点间的距离可以决定减数分裂过程中发生重组染色体的发生率,即重组分数。重组分数的数值将随     

遗传距离

1910年,Morgen TH提出假设:假定沿染色体长度上交换的发生具有同等的几率,那么两个基因位点间的距离可以决定减数分裂过程中发生重组染色体的发生率,即重组分数。重组分数的数值将随着两位点间距离的增大而增大。它是构建物理遗传图谱的基础,也是利用连锁分析将基因序列从染色体上搜寻出来的位置克隆法的基础。人们规定同一染色体上两个位点间在一百次减数分裂发生一次重     

遗传距离

1910年,Morgen TH提出假设:假定沿染色体长度上交换的发生具有同等的几率,那么两个基因位点间的距离可以决定减数分裂过程中发生重组染色体的发生率,即重组分数。重组分数的数值将随着两位点间距离的增大而增大。它是构建物理遗传图谱的基础,也是利用连锁分析将基因序列从染色体上搜寻出来的位置克隆法的基础。人们规定同一染色体上两个位点间在一百次减数分裂发生一次重     

同源多倍化对拟南芥减数分裂前期Ⅰ过程的影响

为研究同源多倍化对拟南芥减数分裂前期Ⅰ过程的影响,以哥伦比亚生态型(Columbia)二倍体拟南芥为试验材料,经0.2%秋水仙素加倍处理,利用流式细胞仪和细胞学方法鉴定倍性,获得同源多倍体拟南芥;分析同源多倍体拟南芥的形态特征,利用荧光显微观察不同倍性拟南芥的减数分裂前期Ⅰ过程,并利用荧光定量PCR技术分析与减数分裂前期Ⅰ过程相关的基因的表达变化。结果表明,与二倍体拟南芥相比,在细胞学水平上,不同倍性拟南芥的减数分裂过程基本一致;在分子水平上,多倍化对拟南芥减数分裂产生一定影响,同源重组相关基因的表达量呈现上调或下调的变化,且功能相关或有相互作用关系的基因的表达量变化趋势相似。     

利用辐射诱发的染色体畸变选育大豆易位系的初探

以５种栽培大豆、４种半野生大豆、２种野生大豆为亲本配制６个杂交组合，对所获得的杂种Ｆ１及亲本以不同剂量Ｃ６０ｏ－γ射线照射，观察花粉母细胞减数分裂染色体行为的变化，特别是探讨诱变的染色体易位条件、频率及遗传效应，以期进行易位系的选育。结果表明，染色体发生易位的频率与基因重组成正相关，在一定范围内，与照射剂量成正比，辐射处理杂交种的易位频率较高，少数易位单株花粉育性低于５０％，具有易位系的特点。     

甘蓝型油菜与黑芥种间杂种基因组亲缘关系研究

以甘蓝型油菜和黑芥为亲本,采用人工杂交并结合胚培养合成了A、B、C三基因组杂种。基因组原位杂交结果显示,在花粉母细胞减数分裂终变期,B基因组染色体以0.41~0.90的频率形成同配二价体,A、C基因组染色体以4.25~5.94频率形成二价体,B基因组与A、C基因组间形成异配二价体的频率在0.96~1.65之间,B基因组与A、C基因有较远的亲缘关系;减数分裂后期I染色体分离极不规律;B基因组染色体分离表现为多样性,2∶6极端分离方式以19%的比例出现;落后染色体、染色体桥及非四分孢子都在减数分裂过程中出现,极端异常的减数分裂是导致花粉不育的重要原因。     

遗传距离

<正>1910年,Morgen TH提出假设:假定沿染色体长度上交换的发生具有同等的几率,那么两个基因位点间的距离可以决定减数分裂过程中发生重组染色体的发生率,即重组分数。重组分数的数值将随着两位点间距离的增大而增大。它是构建物理遗传图谱的基础,也是利用连锁分析将基因序列从染色体上搜寻出来的位置克隆法的基础。人们规定同一染色体上两个位点间在一百次减数分裂发生一次重     

Meiotic recombination in yeast: alteration by multiple heterozygosities

Although meiotic gene conversion has long been known to be accompanied by crossing-over, a direct test of the converse has not been possible. An experiment was designed to determine whether crossing-over is accompanied by gene conversion in Saccharomyces cerevisiae. Nine restriction site heterologies were introduced into a 9-kilobase chromosomal interval that exhibits 22 percent crossing-over. Of all the exchange events that occurred, at least 59 percent of meiotic crossovers are accompanied by gene conversion of one or more of the restriction site heterologies. The average gene conversion tract length was 1.5 kilobases. An unexpected result was that the introduction of as few as seven heterozygosities significantly altered the outcome of recombination events, reducing the frequency of crossovers by 50 percent and increasing the number of exceptional tetrads. This alteration results from a second recombination event induced by repair of heteroduplex DNA containing multiple mismatched base pairs.     

Cre／loxp位点特异性重组系统在转基因植物中的应用

位点特异性重组系统能够在植物遗传转化中更准确、可靠的操纵外源DNA的引入或删除,已成为植物遗传操作中的重要工具。本文简要介绍目前应用最为广泛的Cre/loxp位点特异性重组系统的重组机制,并着重阐述Cre/loxp系统在删除转基因植物中标记基因及定点整合等方面的应用。     

Direct coupling between meiotic DNA replication and recombination initiation

During meiosis in Saccharomyces cerevisiae, DNA replication occurs 1. 5 to 2 hours before recombination initiates by DNA double-strand break formation. We show that replication and recombination initiation are directly linked. Blocking meiotic replication prevented double-strand break formation in a replication-checkpoint-independent manner, and delaying replication of a chromosome segment specifically delayed break formation in that segment. Consequently, the time between replication and break formation was held constant in all regions. We suggest that double-strand break formation occurs as part of a process initiated by DNA replication, which thus determines when meiotic recombination initiates on a regional rather than a cell-wide basis.     

Rad51 is an accessory factor for Dmc1-mediated joint molecule formation during meiosis

Meiotic recombination in budding yeast requires two RecA-related proteins, Rad51 and Dmc1, both of which form filaments on DNA capable of directing homology search and catalyzing formation of homologous joint molecules (JMs) and strand exchange. With use of a separation-of-function mutant form of Rad51 that retains filament-forming but not JM-forming activity, we show that the JM activity of Rad51 is fully dispensable for meiotic recombination. The corresponding mutation in Dmc1 causes a profound recombination defect, demonstrating Dmc1's JM activity alone is responsible for meiotic recombination. We further provide biochemical evidence that Rad51 acts with Mei5-Sae3 as a Dmc1 accessory factor. Thus, Rad51 is a multifunctional protein that catalyzes recombination directly in mitosis and indirectly, via Dmc1, during meiosis.     

Homologous recombination catalyzed by mammalian cell extracts in vitro

An assay was developed to detect recombination events taking place in an in vitro reaction. Extracts of cultured mouse preB lymphocytes were found to catalyze homologous recombination between substrate DNA molecules but not site-specific recombination between cloned mouse immunoglobulin D and J genes. Addition of deoxyribonucleoside triphosphates increased the frequency of homologous recombination. This recombination activity was not observed in two differentiated lymphocyte cell lines.     

加拿大披碱草与老芒麦种间杂种F_1的染色体遗传分析

对加拿大披碱草与老芒麦种间杂种F1的形态学和细胞学特征进行研究。结果表明,F1生长势明显超过双亲,穗型呈双亲中间型;杂种F1的体细胞染色体核型公式为2n=22m＋6sm;F1为真杂种;F1花粉母细胞后期I有落后染色体出现,落后染色体细胞频率达87．37％,减数分裂中期染色体配对紊乱,形成较多的棒状二价体。     

FANCM limits meiotic crossovers

The number of meiotic crossovers (COs) is tightly regulated within a narrow range, despite a large excess of molecular precursors. The factors that limit COs remain largely unknown. Here, using a genetic screen in Arabidopsis thaliana, we identified the highly conserved FANCM helicase, which is required for genome stability in humans and yeasts, as a major factor limiting meiotic CO formation. The fancm mutant has a threefold-increased CO frequency as compared to the wild type. These extra COs arise not from the pathway that accounts for most of the COs in wild type, but from an alternate, normally minor pathway. Thus, FANCM is a key factor imposing an upper limit on the number of meiotic COs, and its manipulation holds much promise for plant breeding.