25. Extranuclear Inheritance（cytoplasmic inheritance)

25. Extranuclear Inheritance（cytoplasmic inheritance)
What is Extranuclear Inheritance ？ How is it produced ? characteristics？ Particles ,Mt and pt ？ Application ？

25 Extranuclear Inheritance
Commonly defined as transmission through the cytoplasm (or things in the cytoplasm, including organelles) rather than the nucleus Generally only one parent contributes

Extranuclear Inheritance
Organelle heredity Organelles that contain chromosomes Chloroplasts and mitochondria Infectious heredity Involves a symbiotic or parasitic association with a microorganism Maternal effect Nuclear gene products are stored in ooplasm and distributed to cells as the fertilized egg divides to form developing embryo

高等生物除了核内作为主要的遗传体系对生物性状的遗传与个体的生长发起着决定性的作用
还有另外的遗传体系——线粒体、叶绿体，除了决定自身功能之外，还与核内体系相互、共同作用，实现特定的功能。一些共生颗粒,如质粒、卡巴等虽没有明确而必须的功能，但也产生表型效应。染色体以外的遗传因子所决定的遗传现象，在真核生物中称为核外遗传或细胞质遗传（extranuclear Inheritance或cytoplasmic inheritance

Chloroplasts and Mitochondria
These organelles contain DNA First explanation for [some] maternal inheritance patterns Endosymbiont theory Analysis of mutant alleles in organelles can be complex because many genes for organelle components are nuclear-encoded And even subunits of a multicomponent enzyme may be partially encoded in both locations Heteroplasmy makes things even worse…

核外遗传的物质基础细胞器基因组细胞质基因组或核外基因组细菌质粒共生生物草履虫放毒型的遗传（细胞内敏感性物质）放毒现象与内共生体
线粒体的遗传叶绿体的遗传禾谷类作物的雄性不育

1 母体影响 2 核外遗传的性质与特点 3 细胞内敏感物质的遗传 4 线粒体的遗传方式及其分子基础 5 叶绿体遗传及其分子基础 6 核外与雄性不育性

第一节母性影响（maternal effects)
通常，核内遗传的特点是，两亲本贡献相等的遗传物质，正交 AA x aa或反交 aa x AA，子代表现一样的。可是有时两种交配结果并不相同，子代的表型受母亲（母本）基因型的影响而和母亲表型一样，这种现象称为母性影响母性影响分为：短暂的母性影响持久的母性影响

Contrasts to Non-Mendelian Genetics Maternal Effect
Animation: Maternal Effect Some maternally-derived phenotypes are produced by the maternal nuclear genome (maternal effect), rather than inherited as extranuclear genes (maternal inheritance). a. Proteins and/or mRNA deposited in the oocyte before fertilization direct early development in the embryo. b. The genes encoding these products are on nuclear chromosomes. No mtDNA is involved.

短暂的母性影响例如：麦粉蛾（E.phestia) 野生型：幼虫皮肤有色—成虫复眼深褐色（这种色素由一种叫做犬尿素的物质形成，一对基因控制）
突变型：幼虫不着色—成虫复眼红色有色个体与无色个体无论 AA X aa 或 aa X AA F1 都是有色的 Aa(有色) Aa(有色) 当F1Aa X aa测交时，有色亲本的性别就会影响后代表型。如果： Aa ♂ ——后代半数幼虫有色，成虫复眼深褐色— 与一般测交结果没什么不同。但， Aa ♀ ——幼虫都是有色的，成虫时红眼、褐眼各半。 Aa♂ X aa♀ Aa ♀ X aa ♂ 幼虫有色无色有色无色成虫褐眼红眼褐眼红眼 1/2Aa /2aa /2Aa /2aa 实际结果幼虫有色无色有色有色成虫褐眼红眼褐眼红眼

结果的解释精子中不带有什么细胞质，而卵里含有大量的细胞质。
当Aa母蛾形成卵子时，无论A卵，还是a卵，细胞质中都含有足量的犬尿素，所以它们的后代中aa幼虫皮肤也是有色的。不过这种母性影响是暂时的，因为aa个体缺乏A基因，不能产生色素，随着个体发育色素逐渐消耗，到成虫时复眼已经成为红色的了。（只影响幼龄期）

Maternal Effect/Maternal Influence
持久的母性影响 Maternal Effect/Maternal Influence Offspring phenotype under control of nuclear gene product present in the egg Genetic information of mother used to produce products present in the egg cytoplasm Snail Limnaea peregra shell coiling is an example

Snail Limnaea peregra Shell Coiling
Hermaphroditic snails Some shells have right-handed (DD or Dd) coiling while others have left-handed (dd)coiling Reciprocal crosses (reverse mail and female genotypes) of true-breeding snails Offspring phenotype depends upon maternal genotype—not maternal phenotype

An example is shell coiling in the snail Limnaea peregra (Figure 15
a. Shell coiling is determined by a pair of nuclear alleles, with the dominant D, producing a dextral (right) coil, and the recessive d producing sinistral (left) coiling. b. The shell coiling phenotype is always determined by the mother’s genotype. c. In all crosses of true-breeding dextral and sinistral snails, the F1s have the same genotype (D/d) but the reciprocal crosses produce different phenotypes (Figure 7.8). i. A dextral female (D/D) crossed with a sinistral (d/d) male produces a dextral F1 (D/d) (Figure 15.14). (1) The F2 genotypes have a 1:2:1 ratio (D/D : D/d : d/d). All F2 snails, including those with genotype d/d, have dextral shells. (2) Selfing the F2 produces an F3 that is 3⁄4 dextral and 1⁄4 sinistral. The sinistral snails are the progeny of F2 d/d mothers (who had dextral shells). ii. A sinistral female (d/d) crossed with a dextral male (D/D) produces a sinistral F1 (D/d). (1) The F2 genotypes also have a 1:2:1 ratio (D/D : D/d : d/d). All F2 snails have sinistral shells. (2) Selfing the F2 produces an F3 that is all dextral, due to the D/d genotype of the F2 mothers (who had sinistral shells).

3. This inheritance pattern is very different from extranuclear inheritance.
a. In extranuclear inheritance, the mother and progeny share a phenotype and an extranuclear genotype. b. In maternal effect, the progeny phenotype is determined by the genotype of the mother, and not by the alleles the progeny carry. 4. In the snail shell example, direction of coiling is determined by the orientation of the mitotic spindle in the first mitotic division following fertilization. Maternal products within the oocyte direct orientation of the mitotic spindle, and thus shell coiling. a. This is supported experimentally: i. When eggs of d/d mothers are injected with cytoplasm from dextral snails, dextral progeny result. ii. When eggs of D/_ mothers are injected with cytoplasm from sinistral mothers, the progeny still have dextral shells. b. Interpretation is that: i. The D allele produces a cytoplasmic product that causes dextral coiling. ii. The d allele does not produce this product, and sinistral coiling is produced by default.

（影响子代终生）这种遗传现象是由于：原来螺类的受精卵是螺旋式卵裂，成体外壳的旋转方向早就决定于最初两次卵裂中纺垂体的方向。第一次卵裂
左旋第二次卵裂右旋实际上也就是母体染色体上的基因决定了子代（影响子代终生）

第二节核外（细胞质）遗传的性质特点母性影响实质上仍是核内基因型的作用，传递方式仍是经典的传递。只不过是来自♀的基因作用，使得父方的显隐性基因延迟一代表现和分离。核外遗传则是由细胞质中的构成要素作用，能自律复制通过细胞质由一代传至另一代。其中最主要的就是叶绿体和线粒体和其他一些核外遗传的物质。叶绿体和线粒体含有DNA、RNA及DNA复制、转录和翻译的完整系统，分别称为叶绿体系统和线粒体系统。它们与核内遗传系统共同组成真核生物中三个相互独立，而又相互联系的遗传体系，因而在遗传学研究中占有重要地位核外的遗传特征是：（1）遗传方式非孟德尔式的，正反交表现不同（2）F1通常只表现母方性状（3）杂交后代一般不出现特定比例的分离

紫茉莉的非孟德尔遗传现象紫茉莉的遗传有几种高等植物有绿白斑植株：紫茉莉（Mirabilis jalapa)、藏报春、假荆芥等。
1909年，法国植物学家 C. Correns报道了紫茉莉中不符合孟德尔定律的遗传现象。紫茉莉的母性影响（质体传递）

Rules of Non-Mendelian Inheritance
1. Extranuclear genes display non-Mendelian inheritance, which has four characteristics: a. Typical Mendelian ratios do not occur, because meiosis-based segregation is not involved. b. Reciprocal crosses usually show uniparental inheritance, with all progeny having the phenotype of one parent, generally the mother because the zygote receives nearly all of its cytoplasm (including organelles) from the ovum. c. Extranuclear genes cannot be mapped to chromosomes in the nucleus. d. If a nucleus with a different genotype is substituted, non- Mendelian inheritance is unaffected.

Fig. 15.6 Variegation in the four o’clock
Peter J. Russell, iGenetics: Copyright © Pearson Education, Inc., publishing as Benjamin Cummings.

Examples of Non-Mendelian Inheritance Shoot Variegation in the Four O’Clock
Animation: Shoot Variegation in the Four O’Clock 1. Variegated-shoot phenotype in four o’clocks involves non-Mendelian inheritance of chloroplasts in the shoots (stem, leaves and flowers). a. Green shoots have normal chloroplasts. b. White shoots have only leucoplasts, which lack chlorophyll, and are incapable of photosynthesis. c. Variegated shoots received both chloroplasts and leucoplasts, which segregated during cell division. Progeny cells are therefore green or white, in a variegated (mixed) pattern (Figure 15.7). 2. Results of crosses between plants with shoots that are variegated illustrate this phenomenon (Table 15.2): a. When ova are from green plants, only green progeny result, regardless of pollen source. b. When ova are from white plants, only white progeny result (but soon die from lack of chlorophyll), regardless of pollen source. c. When ova are from variegated plants, all three types of progeny result, regardless of pollen source.

Fig. 15.7 Model for the inheritance of shoot color in the four o’clock

3. Shoot color in these plants therefore shows a pattern of maternal inheritance. There are three assumptions in the model: a. Pollen contributes no chloroplasts or leucoplasts to the zygote. b. The chloroplast genome replicates autonomously, so that progeny plastids retain the same color phenotype as the original plastid. c. Segregation of plastids during eukaryotic cell division is random, providing some offspring cells with chloroplasts, some with leucoplasts, and some with a mixture.

二、真菌异核体实验核外因子的细胞质传递，在真菌中的异核体实验进一步证实。霉菌或放线菌的菌丝细胞彼此联接并发生融合——异核体。
如:脉孢菌野生型与突变型poky融合--核体--形成分生孢子. 异核体内的两种细胞核将分别出现在不同的分生孢子中，但已经混合的细胞质则不再分开。根据核基因标记，对这些单核分生孢子的后代进行遗传分析，可以看到一些具有野生型核的菌株表现出poky 小菌落性状，而另一些带有小菌落核的菌株却变成了野生型（图14-3）。这一异核体测验的结果说明核的来源对小菌落这个表型性状的发育并无影响，而核外基因才是控制小菌落性状的遗传因子，这种遗传因子通过异核体的细胞质传递给它的无性分生孢子。

第三节细胞内敏感物质的遗传一、草履虫放毒型的遗传
1943年T．M．Sonneborn报导了草履虫（Paramecium anrelia）卡巴粒（Kappa particles，κ）的遗传细胞质的构成要素草履虫（paramecium aurelia)放毒型遗传与细胞一种颗粒有关，并不是所有草履虫都有这种颗粒，因此这种颗粒不是细胞质的构成要素。

Infectious Heredity Cytoplasmic transmitted phenotypes in eukaryotes due to an invading microorganism or particle (e.g. virus)

Kappa in Paramecium Certain strains of P. aurelia are called killer strains because they release paramecin, a substance toxic to sensitive strains Paramecin produced by kappa particles ( per cell) that replicate in cytoplasm Kappa particles contain DNA and protein and require a nuclear gene (K, “little k” strains are sensitive) for maintenance Kappa particles are bacterialike and may contain temperate phage

一个大核—营养核—多倍性草履虫繁殖方式两个小核—遗传相关—二倍性（2）有性生殖—两种: 两个个体结合—交换小核, 自体受精
草履虫繁殖方式两个小核—遗传相关—二倍性（1）无性繁殖一个个体细胞分裂—两各个体（2）有性生殖—两种: 两个个体结合—交换小核, 自体受精

有性生殖中，一种方式是接合生殖，即两个虫体接合，大核消失，各小核经过减数分裂后产生4个单倍体，除保留其中的一个外，其余退化。留下的这个单倍核经有丝分裂，于是每个交配型便各具有两个单倍的小核。接合的两个虫体各将一个小核转移给对方，从而发生了遗传物质交换。虫体分开后，体内的两个小核融合，便形成了一个二倍体核。若两虫体接合时间超过了核交换所需的限度，那么在虫体间也可能通过各接合者之间形成的细胞质桥梁发生细胞质的交换。另一种有性生殖方式是自体受精，即同一个体的两个小核经减数分裂后留下一个小核，这个小核分裂一次后又相互合并，随后再分裂发育成大核和小核。自体受精的后代都是纯合

接合生殖在相互交换小核过程中，大核消失，小核经过减数分裂，相互交换。如AA和aa个体结合，最后形成4个Aa个体。

有性生殖方式，自体受精，既同一个体两个小核经减数分裂后，留下一个小核。这个小核分裂一次又相互合并——然后再分裂发育成一个大核一个小核——不论原来基因型为何样，最后产生的个体都是纯合的。

草履虫——放毒型（杀伤者）——产生一物质(草履虫素)对自身无害，对其它有毒——敏感型——可受害个体
放毒型：K/K+卡巴粒两种因子同时存在（1）细胞质因子 ——卡巴粒kappa k), (2)核基因K，显性敏感型： k/k 交配结合

如果把放毒型与敏感型交配（既接合），由于交换了小核它们双方的基因型都为K/k，其中一个有卡巴粒——产生草履虫素——放毒型
另一个没有卡巴粒——不产 ….——敏感型

若是一个杀伤者（基因型KK）与一个敏感者（kk基因型）只是短暂接合，
一旦二者的接合时间延长，导致细胞质也发生交换，那么，接合的虫体分开后，敏感型由于既有Kk的核基因型，细胞质又有了卡巴粒，也就变成了杀伤者（图14-4）。这表明卡巴粒只是通过细胞质来传递，但是它们的保持却要依赖于核中显性基因K的存在。然而，基因型为Kk的放毒型并不稳定，一旦经自体受精，基因型分离为KK、Kk和kk，kk个体细胞质里的卡巴粒不能保持和增殖，几次无性分裂后，就将因卡巴粒的消失而成为敏感型。由此可知，放毒型的遗传既取决于细胞质里的卡巴粒，同时又受到核基因K的控制。

放毒现象与内共生体草履虫细胞质中没有卡巴粒，可以用微注射法导入，而且草履虫细胞本身有时也可摄入卡巴粒。
反之含有卡巴粒的草履虫在有利于迅速增殖的培养液中培养，可使卡巴粒丢失，可见卡巴粒的最高复制速度还抵不过宿主细胞的分裂速度。卡巴粒还可以被物理化学因素消除。通过深入研究终于在放毒型草履虫中找到了卡巴粒卡巴粒直径约0.2um，相当于一个小型细菌的大小，推测可能为退化的细菌，现在已演化为内共生体（endosymbiont).研究证实，卡巴粒含有DNA、RNA、蛋白质、醣类、酯类等

卡巴粒的rRNA已被分离出来，能和E..Coli DNA杂交，但不能和草履虫DNA杂交，卡巴粒DNA 的碱基成分也与宿主的核DNA和mtDNA不同。
草履虫的卡巴粒不是都有放毒能力。卡巴粒可突变为非放毒型π

二、果蝇的感染性遗传 Infective Particles in Drosophila
CO2 sensitivity Flies fail to recover from CO2 anesthetization (permanently paralyzed) Sensitivity due to presence of virus called sigma Transfer to other insect species unsuccessful, suggesting Drosophila genes essential for its continued propagation/function

在黑腹果蝇中有两个通过雌亲把感染因子传递给后代的例子，都显示出明显的核外遗传形式。
果蝇多数品系CO2所麻醉——恢复——无后遗效应——抗性有些品系相反——CO2敏感敏感性是通过雌体遗传而极少由雄体遗传。 σ病毒样颗粒，它可使雌体变成对CO2敏感。这种σ颗粒引入或是将敏感果蝇的提取物注射到有抗性的果蝇中，都会诱导出敏感性。由此表明，σ是一种感染性因子，能够改变寄主表型，使对CO2具敏感性，通过雌亲的卵子，它能一代一代地遗传下去。

Sex ratio in D. bifasciata and D. willistoni
Some flies produce offspring at an altered sex ratio Mostly female at below 21 degrees Celsius Trait transmitted only to daughters Agent shown to be a protozoan that is lethal only to males And protozoan may have a virus that is actually responsible…

果蝇中核外遗传的另一个例子是关于性比（sex ratio，SR）的现象。
产生大量雌性后代的雌蝇称之为“性比雌蝇”，它们把这种特性遗传给子代中的雌体而不传给雄体。在性比雌蝇的子代中，雄体的缺少可能是由于雄性胚胎在发育早期即已死亡。已经发现果蝇中的这种性比现象也是由一种类似于sigma的螺旋体（spirochete）所引起的。通过繁殖或是注入SR个体的抽提物都能把这种SR性状引人到正常的果蝇体内。和卡巴粒一样，sigma颗粒和SR螺旋体在果蝇中的存在也是取决于相应的核基因。

Infectious Heredity: Killer Yeast 酵母菌中的嗜杀现象
1. Symbiotic bacteria or viruses in eukaryotic cytoplasm may also produce extranuclear inheritance. An example is the killer phenotype in yeast: a. Killer cells secrete a toxin that kills sensitive cells, but not killer strains. b. Killer phenotype results from two cytoplasmic viruses, L and M. Neither virus harms the host cell (Figure 15.12). i. L virus is 4.6 kb dsRNA, in a protein capsid. L-dsRNA encodes capsid proteins used for both viruses, and viral RNA polymerase for replication. ii. M virus is found only in cells also containing L virus. M contains two copies of a 1.8-kb dsRNA. M-dsRNA encodes killer toxin, which also confers immunity on the host cell. c. There are two types of yeast cells sensitive to killer toxin (both lack the M virus): i. Those with the L virus. ii. Those with neither L nor M virus. d. Transmission of these viruses between yeast cells occurs in mating. All progeny of the mating inherit copies of the parental viruses. 2. Killer yeast cells are an example of an infectious mechanism of cytoplasmic inheritance.

第四节线粒体的遗传方式及其分子基础线粒体是各类真核细胞中广泛存在的一类细胞器，为细胞中重要的代谢中心之一。实验证明，三羧循环、氧化磷酸化等反应都是在线粒体的不同部位上进行的。 1963年M．Nass和S．Nass发现线粒体DNA（mitochondrio DNA，mtDNA）以来，对 mtDNA的结构、功能等方面进行了大量的研究，表明线粒体具有半自主性，是细胞中的核外遗传系统，其DNA可为线粒体行使功能所需的rRNA、tRNA以及某些蛋白质（如细胞色素、ATP合成酶）编码。

poky in Neurospora Cytoplasmic/maternal inheritance
Maternal poky x paternal wt all poky Material wt x paternal poky all wt Loss of several cytochromes Hyphae fusions between poky and wt produce heterokaryons (two nuclei) with mitochondria from both parental cells Begins with normal phenotype Become progressively more abnormal (poky) poky is a suppressive mutation Mechanism not clear (loss/modification of wt mitochondria)

Fig. 15.8 Results of reciprocal crosses of [poky] and normal (wild-type) Neurospora

脉胞菌——“缓慢生长”突变型，生长迟缓，呼吸贫弱。与酵母小菌落一样，也是细胞质遗传的，不出现分离的非孟得尔式遗传。
显示出母亲遗传现象：如果突变型po单倍体核♂ X 野生型受精丝中的单倍体核♀结合如果野生型单倍体核核♂ X突变型po单倍体受精丝中的♀结合后代后代

The [poky] Mutant of Neurospora
Saccharomyces petite Mutations The [poky] Mutant of Neurospora 1. Neurospora crassa is an aerobe, and so requires mitochondrial functions to grow. The [poky] mutation in mtDNA has an altered cytochrome complement, leading to slow growth of the fungus. a. Normal Neurospora have cytochromes a + a3, b and c. b. Neurospora with the [poky] mutation lack a + a3 and b, and have an excess of c. 2. Experimental crosses in Neurospora involve fusion of nuclei from mating type A and a parents. Crosses can occur two ways: a. Place both parents on medium at the same time. b. Inoculate one parent onto medium, and add the second parent several days later. The first parent produces all the protoperithecia (fruiting bodies containing the ascospores). 3. Protoperithecia have much more cytoplasm than conidia (asexual spores). a. The strain producing protoperithecia is similar to the female parent. b. The second strain, which contributes conidia, is analogous to the male parent. c. Assigning strains these roles allows reciprocal crosses to be made. i. Protoperithecia from [poky] parent, and wild-type conidia results in all [poky] progeny. ii. Protoperithecia from wild-type parent, and [poky] conidia results in all wild-type progeny. iii. Results show maternal inheritance. d. Tetrad analysis allows correlation of meiotic events with spore organization within the ascus: i. Protoperithecia from [poky] parent, and wild-type conidia results in all [poky] progeny (an 8:0 ratio). ii. Protoperithecia from wild-type parent, and [poky] conidia results in all wild-type progeny (a 0:8 ratio). iii. In the same experiments, nuclear genes segregate at a 4:4 ratio. e. The [poky] allele results from a 4-bp deletion in the promoter for 19S rRNA in the mtDNA, resulting in deficiency of small ribosomal subunits and greatly decreased mitochondrial protein synthesis.

petite mutations give rise to small colonies
Aerobic respiration blocked Live anaerobically S. cerevisiae is a facultative anaerobe Two types Segregational petites encoded by nuclear genes showing Mendelian inheritance cytoplasmic transmission pattern petites Neutral petites demonstrate (give all wt offspring when crossed to wt) Suppressive petites (behave like poky in Neurospora)

1. Yeast can grow either anaerobically by fermentation (slow growth) or aerobically using mitochondria (fast growth), forming colonies from single cells on solid media. 2. Yeast petite colonies are much smaller than those formed by wild-type cells, due to cytochrome deficiencies that prevent aerobic respiration. a. On a medium that supports only aerobic respiration, petite cells are unable to grow. b. The spontaneous mutation rate is 0.1–1%, but exposure to an intercalating agent (e.g., ethidium bromide) raises the rate to 100%. c. This allows isolation of different petite cell lines, containing different mutations. 3. Yeast crosses between petite and wild-type cells (a X α crosses) determine the mechanism of inheritance for this phenotype. a. The zygote formed from mating is grown into a colony to check its phenotype, and when it sporulates by meiosis, the tetrad of ascospores can also be grown into colonies for phenotype analysis. b. Some petite X wild-type crosses give 2:2 segregation (wild-type:petite). i. This is the same ratio as seen in nuclear genes, so these petite mutants are nuclear (segregational) petites, written pet- (Figure 15.9). ii. The cross in this case was pet- X pet+. Diploid was pet-/pet+ (hence wild-type) and the spore tetrad contained 2 pet- and 2 pet+ spores. Yeast petite Mutants

petite Mutant Crosses

Fig. 15.9a Inheritance of yeast petite mutants

c. Another class of petite mutants is the neutral petites ([rho-N]).
i. When crossed with wild-type ([rho-N] X [rho+N]) produce wild-type diploids ([rho-N]/[rho+N]) and spores that segregate 0:4 (no petite : 4 wild-type). ii. This is an example of uniparental (not maternal, since gametes are same size) inheritance. iii. In [rho-N] mutants, nearly 100% of the mtDNA is missing, and so mitochondrial functions are also missing. iv. Spores produce only wild-type colonies because normal mitochondria from the wild-type parent provide normal mitochondria for the progeny. The petite trait thus is lost after one generation. d. Most petite mutants are of the suppressive ([rho-S]) type. They differ from neutral petites by having an effect on the wild-type, although both are mutations in mtDNA. i. A [rho+/rho-S] diploid has a respiratory-deficient phenotype, and if it divides mitotically the progeny will nearly all be petites. ii. Sporulation of the petite [rho+/rho-S] diploid produces tetrads with a 4:0 (petite : wild-type) ratio. iii. Sporulation of the rare wild-type [rho+/rho-S] diploid produces tetrads with a 0:4 (petite : wild-type) ratio. iv. Suppressive petite mutants start with deletions in mtDNA. The amount of mtDNA is restored by duplications of existing mtDNA, often creating gene deletions and rearrangements that cause deficiencies in the enzymes for aerobic respiration. v. The suppressive effect over normal mitochondria might result from either: (1) Faster replication of the mutant mitochondria, outcompeting wild-type, or (2) Fusion with normal mitochondria and recombination between [rho-S] mtDNA and wild-type mtDNA.

Fig. 15.9b Inheritance of yeast petite mutants

Fig. 15.9c Inheritance of yeast petite mutants

Organization of Extranuclear Genomes Mitochondrial Genome
1. Mitochondrial functions include energy-generating oxidative reactions requiring a variety of enzymes, including: a. Pyruvate dehydrogenase. b. Electron transport and oxidatiyphosphory1ation enzymes. c. Citric acid cycle enzymes. d. Fatty acid oxidation enzymes 2. Mitochondrial genomes (mtDNA) are sequenced for several species. a. Many are circular, double-stranded and supercoiled (Figure 15.1). Linear genomes occur in mitochondria of some protozoa and fungi. b. GC content of mtDNA often differs from nuclear DNA, allowing separation by CsCl density gradient centrifugation. c. Mitochondrial DNA lacks histone-like proteins. d. Multiple genomic copies are in multiple nucleoid regions within the mitochondrion. e. Gene content is conserved across species, but size of the mtDNA varies widely: i. Animal mtDNA is less than 20 kb (human is 16,569 bp). Essentially all of this DNA encodes products. ii. Yeast mtDNA is about 80 kb, and not all of this DNA encodes products. iii. Plant mtDNA ranges from 100 kb to 2 million base pairs. Not all encodes products.

Fig. 15.2 Model for mitochondrial DNA replication that involves the formation of a D loop structure

3. Replication of mtDNA is semi-conservative, uses mitochondrial DNA polymerases and RNA primers, and involves no proofreading. a. Replication of mtDNA occurs throughout the cell cycle. (Contrast with nuclear DNA, which replicates only in S phase.) b. Both strands of mtDNA in most animals replicate in a continuous manner, with replication of one strand initiating well before the other. 4. Mitochondria are not synthesized de novo, but arise from growth and division of preexisting mitochondria (Luck, 1963). Some of their genetic information is in the mitochondrial chromosome, the rest in the nuclear DNA. a. The mtDNA map (Figure 15.3) contains information for: i. tRNAs. ii. rRNAs. iii. Some polypeptide subunits of cytochrome oxidase, NADHdehydrogenase, and ATPase. b. Nuclear DNA encodes other mitochondrial components, including: i. DNA polymerase and other replication proteins. ii. RNA polymerase and other transcription proteins. iii. Ribosomal proteins, translation factors, aminoacyl tRNA synthetases. iv. The other subunits of cytochrome oxidase, NADH-dehydrogenase and ATPase. c. The mtDNA has genes on both DNA strands. They were identified in two ways: i. Computer-based search for ORFs (also called URFs, unidentified reading frames). ii. Aligning 5’ and 3’ sequences of mitochondrial mRNAs with the corresponding mtDNA sequence. iii. All known human mtDNA ORFs have been assigned a function

Fig. 15.3 Map of the genes of human mitochondrial DNA

5. Mitochondrial ribosornes translate mRNAs from the mitochondrial chromosome within the organelle. For example, human mitochondrial ribosomes: a. Have two subunits, 45S and 35S, forming a 60S mitochondrial ribosome. b. Have only two rRNAs, 16S rRNA in the large subunit, and 12S rRNA in the small subunit. c. Usually have only one gene for each rRNA in the mtDNA. d. Ribosomal proteins are usually encoded by nuclear DNA, and move into the mitochondria from the cytoplasm. 6. Mammalian mtDNA is transcribed into a single large RNA molecule that is cleaved to produce mRNAs, tRNAs and rRNAs. These RNAs are then processed: a. mRNAs receive 3’ poly(A) tails. b. tRNAs receive 3’ CCA sequences. c. Mitochondrial mRNAs have no 5’ caps. 7. The much larger mitochondrial genomes of yeast and plants differ from animal mitochondria: a. tRNA genes do not separate genes, and other DNA sequences signal transcription termination. b. Large gaps occur between genes in the mtDNA. c. Introns are found in mitochondrial genes from these organisms, but never in animal mtDNA genes. d. mtDNA sequences encoding some mRNAs do not include a complete stop codon. Instead, the 3’ end is U or UA, and the poly(A) tail completes the stop codon (UAA).

8. Translation of mitochondrial mRNAs is distinct from cytoplasmic translation:
a. Mitochondrial mRNAs do not have a 5' cap. i. Yeast and plant mRNAs have a 5' leader sequence, and so initiation can occur at the first AUG codon. ii. Animal mitochondria lack the leader sequence, and so initiation must occur in a unique way. b. In translation, mitochondria have similarities to bacteria: i. Both use fMet-tRNA in initiation. ii. Mitochondrial initiation (IF), elongation (EF) and release (RF) factors are distinct from those in the eukaryotic cytoplasm. iii. mt ribosomes are sensitive to the same agents as bacterial ribosomes (e.g., streptomycin, neomycin, chloramphenicol). iv. mt ribosomes are insensitive to agents that inactivate eukaryotic cytoplasmic ribosomes (e.g., cycloheximide). v. These sensitivities are used in research to determine which proteins derive from nuclear DNA, and which from mtDNA. c. Only plant mitochondria use the “universal” genetic code. Others have differences that show no single pattern (Table 15.1). d. Mitochondria show extended wobble in base pairing of tRNA with codon, allowing translation with only 22 tRNAs (compared with 32 tRNAs theoretically needed for translation using standard wobble). e.. Structural features that never differ in cytoplasmic tRNAs sometimes do differ in mitochondrial tRNAs.

Fig Synthesis of the multisubunit protein cytochrome oxidase takes place on both cytoplasmic and mitochondrial ribosomes Peter J. Russell, iGenetics: Copyright © Pearson Education, Inc., publishing as Benjamin Cummings.

9. Analysis of mtDNA can reveal genetic relationships. In humans:
a. There is a 400-bp polymorphic region. b. Mitochondria are maternally inherited, and so maternal-line relations can be analyzed using PCR. c. An example involves a woman's claim be Princess Anastasia of Russia, sole member of the Royal Romanov family to survive the Bolshevik Revolution (1917). i. Remains of the executed royal family matched mtDNA of living members related through maternal lines. ii. The woman's mtDNA did not match the mtDNA of living members related through maternal lines. Thus, she was not Anastasia. d. Conservation biology also uses mtDNA analysis to determine genetic variability in populations (e.g., grizzly bears in Yellowstone Park).

一、酵母的小菌落突变线粒体细胞中代谢中心之一，是产生呼吸酶和一些其它酶的地方。呼吸酶缺少，会影响细胞的生长。所以某些“生长迟缓”的突变与线粒体有着密切的关系。如酵母菌（Saccharomyces cerevisiae）的小菌落。酵母菌与脉胞菌一样，是一种子囊菌。有性生殖——4个子囊孢子——一个个地分离开来，分别培养，进行遗传分析。

酵母小菌落的遗传 1940，Boris Ephrnssi发现酵母小菌落大菌落大菌落＋1-2％小菌落小菌落小菌落

从一个酵母菌开始，让它由无性的方式增殖，长城一个培养物。按理这个培养物应该是均一的。
取一点儿菌样，涂布在固体培养基上，每一个酵母长成一个菌落。可是其中有一小部分菌落（约1-2%）比其它菌落小得多——所谓的“小菌落” 小菌落酵母菌缺少细胞色素a和b以及细胞色素c氧化酶，所以在正常通气条件下，这些“小菌落”细胞比正常细胞长得慢——而成为小菌落——很稳定——不再回复到正常的大菌落大菌落大菌落 + 小菌落（1-2%）小菌落小菌落

1小菌落与正常酵母菌交配 2只产生正常二倍体合子 3减数分裂后产生的单倍体也是正常的 4小菌落性状消失了，表现为细胞质遗传
染色体上的基因A、a还与预期一样，子囊中4个孢子出现1：1的比例

线粒体遗传柳叶菜属的细胞质遗传 23年，连续回交25代，仍表现E.luteum的特征米卡里斯（Michaelis）
E.luteum x E.hirsutum 黄花柳叶菜刚毛柳叶菜 F1 正反交结果不一样 23年，连续回交25代，仍表现E.luteum的特征

二、线粒体基因组（mtDNA)多样性线粒体DNA分子是双链分子，主要是环状，少数是线状。线粒体基因组大小变化较大，
1962年Ris，1963年Nass分别观察到线粒体内有线状DNA 线粒体DNA分子是双链分子，主要是环状，少数是线状。线粒体基因组大小变化较大，动物为14～39kb，一般动物36kb；真菌类17～176kb，酵母菌85kb、链霉菌64kb、衣藻15kb。；四膜虫属（ Tetrahymena）和革履虫等原生动物为50kb，是线性分子。植物的线粒体基因组比动物的大15～150倍，也复杂得多，大小可从200kb到2500kb，如在葫芦科中，西瓜是330kb，香瓜（Cucumis melon L.）是2500kb，相差7倍。

线粒体DNA 核DNA，mtDNA和cpDNA的性质

真核生物每个细胞内含众多的线粒体，每一线粒体又可能具有多个线粒体DNA分子。
通常，线粒体愈大，所含的DNA分子愈多。在线粒体DNA的组成方面，绝大多数的mtDNA中没有重复核苷酸序列，这是mtDNA一级结构的重要特点哺乳动物mtDNA的D－loop区（也称控制区）总长约1000bP左右，为非编码区，是线粒体基因组中进化速度最快的 DNA序列，特别适合于种内群体水平的研究。

线粒体DNA的特点：与核DNA相比，比核DNA小。与核DNA相比， GC含量不同，密度有差别。
一般动物线粒体DNA是闭合环状的，（四膜虫、草履虫mtDNA线状）周长为5－6u，但是原生生物和植物线粒体DNA要长得多（15－30u)。线粒体DNA携带有遗传信息，半保留复制。

酵母线粒体基因组编码： 3个rRNA基因(26s,18s,5s) 14个tRNA基因核糖体蛋白基因rps4，rps13，rps14 细胞色素C氧化酶复合体基因coxI，coxII，coxIII ATP酶复合体基因atpA1，atpA2，atpA6，atpA9，atpA10 NADH脱氢酶复合体I基因：ND-1，DN-5

特点：三、人类线粒体基因组的结构特点 1981年，B. Borst和L. A. Grivell等测定了人类线粒体基因组的DNA序列。
小而基因排列紧密。 mRNA没有5’帽结构。 22个tRNA分子用于线粒体的蛋白合成。 4个密码子不同于核基因。

遗传密码不是唯一的！研究mtDNA的翻译发现密码表不是唯一的。

在线粒体中密码子的改变

Mitochondrial Genes/Expression
mtDNA is circular, generally relatively small 16-18 kbp in mammals, 75 kbp in yeast, but 367 kbp in Arabidopsis (a mustard plant) 5-10 copies/organelle in vertebrates, in plants Introns generally absent, small intergenic spaces in small mtDNAs, reverse in larger ones such as yeast Genetic code similar but modified Encodes rRNAs, tRNAs and 13 polypeptides in humans (portions of electron transport chain)

Mitochondrial Genes/Expression
Protein synthetic apparatus combination of mtDNA and nuclear-encoded But nuclear-encoded proteins distinct from their cytoplasmic or nuclear counterparts RNAP is single polypeptide and is inhibited by rifampicin/rifamycin But sensitive to antibiotics targeted normally against prokaryotes Ribosomes range from 55-80S

Many proteins encoded by nuclear genes have products transported to mitochondria and RNAs ….

第五节叶绿体遗传及其分子基础 1962年Ris 和Plaut用电镜发现在衣藻、玉米等植物叶绿体基质中20.5nm的纤维，用DNase处理后消失，证实了DNA的存在。

Examples of Non-Mendelian Inheritance Shoot Variegation in the Four O’Clock
Animation: Shoot Variegation in the Four O’Clock 1. Variegated-shoot phenotype in four o’clocks involves non-Mendelian inheritance of chloroplasts in the shoots (stem, leaves and flowers). a. Green shoots have normal chloroplasts. b. White shoots have only leucoplasts, which lack chlorophyll, and are incapable of photosynthesis. c. Variegated shoots received both chloroplasts and leucoplasts, which segregated during cell division. Progeny cells are therefore green or white, in a variegated (mixed) pattern (Figure 15.7). 2. Results of crosses between plants with shoots that are variegated illustrate this phenomenon (Table 15.2): a. When ova are from green plants, only green progeny result, regardless of pollen source. b. When ova are from white plants, only white progeny result (but soon die from lack of chlorophyll), regardless of pollen source. c. When ova are from variegated plants, all three types of progeny result, regardless of pollen source.

Chloroplasts Carl Correns A codiscoverer of Mendel’s work
Worked with four o’clock plants (Mirabilis jalapa) Had branches with either white, green or variegated leaves Type of offspring dependent only upon the phenotype of the branch from which the ovule was derived—not the pollen F(figure 9-1) Concluded that leave color was dependent upon the chloroplasts and that these or other factors were contributed through the ovule cytoplasm

Four O‘Clocks

3. Shoot color in these plants therefore shows a pattern of maternal inheritance. There are three assumptions in the model: a. Pollen contributes no chloroplasts or leucoplasts to the zygote. b. The chloroplast genome replicates autonomously, so that progeny plastids retain the same color phenotype as the original plastid. c. Segregation of plastids during eukaryotic cell division is random, providing some offspring cells with chloroplasts, some with leucoplasts, and some with a mixture.

Pelargonium 天竺葵

衣藻的叶绿体遗传在叶绿体遗传研究方面，莱因衣藻(Chlamydomonas reiuhardi)是所用材料中研究得最为详尽者之一.它的营养细胞通常含有一个单倍体的核、一个叶绿体和约20个线粒体。衣藻通常行无性繁殖，有时通过两种形态学上相同但交配型不同的配子进行融合，行有性生殖。衣藻的交配型，是由细胞核内一对等位基因mt+和mt-所决定的。配子融合给合子提供了相等的细胞内含物，合子萌发时，通常立即发生减数分裂，其4个单倍体产物，核基因是按2：2分离。

但是，有一些基因如影响光合作用能力的基因、某些抗性基因则都表现为母性遗传。这种现象最早发现于从衣藻中分离得到的突变体sm-2，这是一种对链霉素具有高度抗性的突变体，把它与野生型杂交，其子代的链霉素抗性依亲本交配型不同而异. 即当链霉素抗性型亲本的交配型是mt+时，几乎所有的子代(通常大于99％)也是链霉素抗性型. 如果敏感型是mt+，则几乎所有子代都是链霉素敏感型，显示非孟德尔式遗传。

Chlamydomonas Chloroplast Mutations
Unicellular alga Haploid Mating gives diploid cell that immediately undergoes meiosis to form haploid cells Single chloroplast with 50 copies of cpDNA mt+ and mt- strains strS and strR strains (streptomycin resistance)

Offspring of strS and strR Crosses
always have str phenotype of mt+ parent Only mt+ parent donates cytoplasm But 50% of offspring mt+ and 50% mt- mt encoded by nuclear gene Mitochondrial encoded phenotypes also are inherited in a uniparental manner But the mtDNA comes from the mt- strain (note the change) Note streptomycin is an antibiotic commonly used to kill bacteria/prokaryotes…

strS and strR Crosses

1954年，Sager smrmt+×smsmt- sms mt+ ×smrmt- 95%以上smr %以上sms

为对上述观察提供一些直接的证据，R．Sager等用15N标记一种交配型的DNA，然后用这种配子同含有正常14N的其他配子进行杂交。交配后6h发现，如果含15N的配子是mt-，合子中的叶绿体DNA只含14N; 而若是含15N的配子是mt+，则合子中的叶绿体DNA就只含15N。

衣藻核外遗传的原因杂交合子 cpDNA浮力密度 14Nmt＋×14Nmt－ 1.69 15Nmt＋×15Nmt－ 1.70

由此看来，只有从mt+亲本来的叶绿体DNA传递下来，而从mt-亲本来的叶绿体DNA则被丢失了。这样一种特殊的母性遗传现象并不只限于链霉素抗性，其他一些性状的遗传也符合这一规律，可见它还取决于mt+和mt-细胞的其他特性。按照Sager等的见解，这一特殊母性遗传现象可能是由于mt+细胞中存在着限制-修饰酶系，使来自mt-的叶绿体DNA被降解。

Fig. 15.11 Uniparental inheritance in Chlamydomonas

三、叶绿体遗传系统与核遗传系统的关系玉米埃型条斑遗传
埃型条斑(striped iojap trait)，有关的基因iojap(ij)位于玉米核基因组的第7连锁群具有ij/ij纯合子的玉米植株或是不能成活的白化苗，或是在茎和叶上形成有特征性的白绿条斑。当这种植株作为父本用来给正常的(+／+)绿色植株授粉时，条斑性状按孟德尔规律遗传(图14-10A)。而当ij/ij玉米用作母本与绿色父本杂交时，子代中看不到典型的孟德尔比例，它们的表型可以是绿、白或条斑型(图14-10B)。

可见，埃型条斑一旦在纯合体ij／ij雌性植株中出现，就可以通过母体遗传下去，这一种特性形成后就与其核基因无关了。显示出典型的细胞质遗传，而不论植株的核基因型如何，甚至是在该座位上替换了一个正常基因，使其核基因型为+／+，也不足以把由原来ij核基因效应所造成的叶绿体DNA中的突变“矫正”过来。从玉米埃型条斑的例子显示，一方面叶绿体这种细胞器在遗传上有其自主性，另一方面，叶绿体受到核基因突变效应的影响可以发生改变。

玉米埃型条斑（ijij），属第七连锁群。
P IjIj （绿色） X ijij（条斑） F Ijij （绿色） F IjIj （绿色）：2 Ijij （绿色）：1 ijij （条斑） P ♀ ijij （条斑） X ♂ IjIj （绿色） F Ijij （绿色） Ijij （条斑） Ijij （白色） F1 ♀ Ijij （条斑） X ♂ IjIj （绿色） IjIj （绿色） IjIj （条斑） IjIj （白色） Ijij （绿色） Ijij （条斑） Ijij （白色）

Chloroplast Genome 1. Chloroplasts have a double membrane, internal lamellar structure containing chlorophyll, and protein-rich stroma. Chloroplasts divide and grow in the same way as mitochondria. 2. The chloroplast genome (cpDNA) is not as well characterized as mtDNA, but some things are known: a. Structurally, cpDNA is similar to mtDNA. It is dsDNA, a supercoiled circle lacking structural proteins. b. The GC content of cpDNA often differs from both nuclear and mtDNA, allowing separation on CsCl density gradients. c. The size of cpDNA varies from 80 kb-600 kb. All chloroplast genomes carry noncoding DNA. d. Each chloroplast has multiple copies of cpDNA in several nucleoid regions. An example is Chiamydomonas with 500-1,500 cpDNA molecules per chloroplast. 3. Nuclear genes encode some chloroplast components, while cpDNA genes (which may include introns) encode the rest, including (Figure 15.5): a. Two copies of each chloroplast rRNA (l6S, 23S, 4.5S and 5S). The copies are included with other genes in inverted repeats designated IRA and IRB that define the short (SSC) and long (LSC) single copy regions of the cpDNA. b. The tRNAs (30 in tobacco and rice, 32 in the liverwort Marchantia). c. Almost 100 highly conserved ORFs. Approximately 60 are now correlated with proteins needed for chioroplast transcription, translation aiid photosynthesis.

2、叶绿体遗传的分子基础紫茉莉绿白条斑、玉米埃型条斑都是有关叶绿体是色泽和分化。前面已经提到，叶绿体有其自身的遗传系统，细胞分裂叶绿体大致均等分离。所以叶绿体性状大都由结种子的亲本传递。 cpDNA (ctDNA)

(一)叶绿体基因组叶绿体基因组是一个裸露的环状双螺旋分子，大小一般变动在120kb至217kb之间。
通常一个叶绿体中可含一至几十个这样的DNA分子。叶绿体基因组的碱基序列中不含5’—甲基胞嘧啶，这一特点可作为鉴定叶绿体DNA提纯程度的指标。根据变性—复性、叶绿体DNA核苷酸序列的分析，都表明大多数植物的叶绿体基因组有一个共同的特征，即含有两个反向重复序列。它们之间由两段大小不等的非重复序列所隔开。由于重复序列方向相反，所以在复性过程中每条单链上的两个重复序列恰好可以互补形成双链结构，而它们间的两个非重复区则形成两个大小不等的单链DNA环，分别称为大小单拷贝区。不同植物中大、小单拷贝区的长度不一。

Fig. 15.5 Organizations of the chloroplast genome of rice (Oryza sativa)

4. Chloroplasts have 70S ribosomes consisting of 50S and 30S subunits.
a. The 50S subunit includes a 23S, 5S and 4.5S rRNA. b. The 30S subunit includes a 16S rRNA. c. Ribosomal protein number is unclear. Some proteins are encoded in nuclear DNA, others in cpDNA. d. Translation is similar to prokaryotes: i. Initiation uses fMet-tRNA. ii. Chloroplast-specific initiation (IF), elongation (EF) and release (RF) factors are used. iii. The universal genetic code is used. e. Chloroplast ribosomes have the same antibiotic inhibition profile as mitochondria, and can be studied in the same way. Ribulose bisphosphate decarboxylase is an example: i. This enzyme controls the first step in photosynthetic fixation of carbon. It is the most prevalent protein on earth. ii. The enzyme contains four identical small peptides (encoded by nuclear DNA) and four identical large peptides (encoded by cpDNA).

但是，在蚕豆、豌豆等一些豆类叶绿体DNA中至今尚未检测出重复序列，而眼虫的Z—Ha品系中却有3个紧密排列的重复序列。
叶绿体DNA能够自我复制。但和线粒体DNA一样，叶绿体DNA的复制酶及许多参与蛋白质合成的组分都是由核基因编码，在细胞质中合成而后转运入叶绿体。叶绿体基因组含有自己的转录翻译系统。它的核糖体属于70S型，组成50S和30S小亚基的23S、4.5S、5S和16SrRNA基因都由叶绿体DNA编码。叶绿体核糖体蛋白质基因组中约有l／3也是叶绿体DNA编码，另外叶绿体基因组还含有30多个tRNA基因的编码序列。

类囊体： RubP羧化酶大亚单位 19个叶绿体核糖体蛋白转译起始因子IF-1 转译延长因子EF-Tu
DNA聚合酶的、 、  单位 4个rRNA23s,16s,5s,4.5s 40个tRNA 类囊体： PSI:P700的A1,A2原蛋白 PSII:32KD P680原蛋白细胞色素b559蛋白光合作用电子传递蛋白叶绿体ATP酶复合体B,A,E,III等亚单位

Chloroplast Genes/Expression
Chloroplasts have circular DNA and a complete gene expression system Components derived from cpDNA and nuclear DNA encoded genes cpDNA commonly kbp in size No nucleosomes, but has introns and large intergenic regions Multiple copies/organelle (75 in Chlamydomonas) and recombination can occur Encode rRNAs, tRNAs, rproteins (~70S ribosome) and other proteins/enzymes (92 encode thylakoid proteins in the liverwort)

质体DNA与核内DNA 藻类中叶绿体DNA的含量比核内DNA少得多。
质体DNA不与组蛋白结合形成复合体，与E.coli相似。细胞核内DNA有25％左右的胞嘧啶是甲基化的，而叶绿体DNA则没有。质体DNA有一整套合成蛋白质的结构。质体DNA可以自我复制，具有一定的独立性和稳定性，呈不均等分离。对水稻、烟草等叶绿体的基因组分析，已知的基因总数为146个，其基因产物分布在基质和类囊体上。

Origin of Mitochondria and Chloroplasts
1. Endosymbiosis is believed to account for mitochondria and chloroplasts. a. Mitochondria appear to be derived from a photosynthetic purple nonsulfur bacterium that entered a eukaryotic cell about a billion (109) years ago. They provide oxidative phosphorylation to the cell. b. Chloroplasts appear to derive from entry of a photosynthetic cyanobacterium. 2. Many proteins of both mitochondria and chloroplasts are encoded by nuclear genes, indicating that genes have moved from the organelles to the nuclear DNA.

Mitochondrial/Chloroplast Evolution
Endosymbiont theory – Lynn Margulis Mitochondria and chloroplasts arose independently about 2 billion years ago as free-living prokaryotes Primitive eukaryotes without these abilities engulfed the prokaryotes as endosymbionts Relationship ultimately changed to that of an organelle Organelles have circular DNA Most genes moved to “nucleus” (<10% remain) Targeting peptides added Organelle genes/expression still “prokaryotic”

MtDNA 与人类进化 mtDNA variations suggest region where modern humans emerged

第六节植物雄性不育第六节核外遗传与植物雄性不育性
第六节植物雄性不育植物花粉败育的现象称为雄性不育性(male sterility)。雄性不育性在植物界较为普遍，已在多种植物中发现。根据雄性不育遗传的机制，大抵可以分为核不育类型和质-核不育类型。

一.不育类型核不育:由核内染色体上基因决定的雄性不育类型。质不育核-质互作不育配子体与孢子体不育
核不育型多属自然发生的变异，如在水稻、小麦、玉米、谷子等作物中均曾发现过，但总的说来，目前发现的核不育现象还比较少，往往因为不能产生后代而被淘汰。有少数例外，它们能通过环境因素调节而恢复育性保存后代。如湖北的光敏核不育水稻、山西的太谷核不育小麦等。核不育型的败育过程发生于小孢子母细胞减数分裂期间，不能形成正常花粉。由于败育过程发生较早，败育彻底。

遗传学试验证明，多数核不育类型都受核内一对隐性基因(ms)控制，纯合体(ms／ms)表现雄性不育。其不育性可被相对的显性基因(Ms)所恢复，杂合体(M5／ms)后代呈简单的孟德尔式分离。因此，用普通遗传学方法不能使核不育型的整个后代群体保持不育性。这是核不育类型的一个重要特征，也正是由于这一点，核不育类型的利用受到很大的限制。

可遗传的植物雄性不育性 1921年Bateson 和 Gairdner 报道了亚麻雄性不育现象。匍匐茎 x 高杆正常可育正常可育
正常可育正常可育 F1 正常雄性可育 F2: 3/4雄性可育 /4 雄性不育

F2 S(RfRf) S(Rfrf) S(rfrf)
亚麻的雄性不育的遗传解释 1927年 Chittenden 和 Pellew 对亚麻的雄性不育遗传进行了完整的解释。 S(RfRf) x N(rfrf) 匍匐茎可育高杆可育 F1 S(Rfrf) F2 S(RfRf) S(Rfrf) S(rfrf) 3/4 雄性可育 /4 雄性不育

植物雄性不育一型说、二型说和三型说核不育类型质－核不育类型 40年代Sears 提出雄性不育的三型说
1956年Edwardson 提出二型说 60年代Kihara 与S. S. Maan 提出一型说核不育类型核基因决定质－核不育类型不育的胞质基因和相对应的核基因共同决定。

雄性不育花粉败育的两种类型孢子体不育如小麦的T型不育系、高粱的A型不育系等 RfRf Rfrf rfrf 配子体不育如水稻的B型不育系、玉米的M型不育系 Rf rf

三系两区制种法－雄性不育的应用三系雄性不育系S(rfrfr) 保持系N(rfrf) S(rfrfr) x N(rfrf) 保持系
S(rf rf) x N(RfRf) 或 S(RfRf) 恢复系两区雄性不育和保持系间作恢复系和优良性状不育系间作

玉米的三系两区育种法雄性不育和保持系间作恢复系和优良性状不育系间作

袁隆平－－世界杂交水稻之父

二、线粒体与雄性不育性玉米不育系由于恢复育性的核基因不同而分为3类：cms-S、cms-C和cms-T。它们的线粒体DNA限制性酶切图谱与其相应保持系的酶切图谱之间存在明显的差异，且三者彼此之间也不相同。 cms-S Rf3 cms-C Rf4 cms-T Rf1l和Rf2 有关玉米T型不育系的研究发现，其线粒体DNA有一个特异的3547bp的核苷酸序列，它含有两个长的可读框(ORF)：T-ORFl3和ORF25。前者编码一个相对分子质量为1296D的多肽，后者则可能编码一个相对分子质量为2454D的多肽。

经RNA印迹法(Northern blotting)表明，T-orf13只能与T型细胞质中的转录产物杂交，从而证明了它与玉米T型不育性的相关性。T-orfl3编码的相对分子质量为1．3×104多肽广泛存在于cms-T玉米所有器官的线粒体膜中。蛋白质印迹法(Western blotting)、免疫学分析都证实相对分子质量为1．3×104多肽分布于线粒体膜上，可能与ATP酶有某种联系，在分离的细胞色素c氧化酶中也观察到它的存在。现已知育性恢复基因Rf1可以特异性地抑制T—orf13的表达，使相对分子质量为1．3×104多肽的含量减少约80％。而其隐性等位基因rf1则不影响T-orf13的表达。初步的研究表明，Rfl可能影响T-orfl3的转录过程，但其控制机制还不清楚。

三、叶绿体与雄性不育性叶绿体DNA与雄性不育性的有关报道最早见于烟草和棉花。以后人们发现玉米正常品系与不育品系的叶绿体DNA的限制酶谱仅有微小差异，又利用双向电泳技术进一步鉴定出叶绿体DNA的一些变化与胞质雄性不育有关。我国科学院遗传所的有关实验室自20世纪70年代末即开展了有关雄性不育机理的探讨。他们选用玉米、小麦、油菜等的雄性不育系及相应保持系为材料，通过DNA的热变性分析、酶切消化、琼脂糖凝胶电泳比较等，揭示了雄性不育与叶绿体DNA的关系。尤为有意义的是以油菜及萝卜为材料进行了叶绿体特异片段的克隆、定位及序列分析工作，

其结果不仅显示出不育品系与相应可育品系叶绿体DNA之间存在某种差异，而且发现萝卜及油莱中与花粉育性特异性有关的叶绿体DNA片段均位于rRNA基因所在的反向重复区中，并确定了该片段在此重复区的具体位置。 20世纪80年代初期，在玉米叶绿体和线粒体基因组的研究中就发现，这两种基因组有长约12．1kb的同源区，其同源性大于90％。这段序列包括16S rRNA基因和两个tRNA及l，5—二磷酸核困糖羧化酶大亚基的基因片段。而且玉米3种雄性不育类型的改变，都与这一同源区序列的改变有关。这一结果与我国科学工作者在萝卜、油菜中的发现正好彼此印证。这就进一步证明了该同源序列的变化，不仅同单子叶植物中的玉米，也可能同双子叶植物中的油菜、萝卜的小孢子不育性的改变有关

对可育与不育品系叶绿体蛋白质的比较也获得有意义的发现。如高粱、小麦、玉米、水稻、油菜、烟草等许多作物不育系与正常品系的RuBP羧化酶活性存在明显差异。此外，油菜不育系与可育系的叶绿体类囊体膜上ATP酶偶联因子的一个亚基β-CD也存在差异，而它们都是由叶绿体自身DNA编码的。高等植物的雄性不育性是杂种优势利用的一条重要途径，雄性不育所涉及的作物种类逐年增多，利用范围日趋广泛，从而受到世界各国农业工作者的重视。但是有关雄性不育性遗传机理的研究并不充分。随着分子遗传学的发展，雄性不育性的研究也被推进到一个新的历史阶段，并已先后从线粒体遗传和叶绿体遗传的角度进行了一些探索，取得了一定的成果，启迪了人们对雄性不育性的思考，然而要最终解决这个问题，还有待于更深人细致的探求。

线粒体突变与人类遗传 mtDNA has a high rate of mutation
10 times more rapidly than the nuclear DNA (vertebrate) myoclonic epilepsy and ragged red fiber disease (MERRF线粒体脑肌病) Leber’s hereditary optic neuropathy (LHON) Leber遗传性视神经病(LHON) mtDNA mutations and aging mtDNA积累氧化损害16倍于nDNA,主要影响ATP合成

mtDNA Mutations and Human Genetic Disorders
Human mtDNA is 16,569 bp Encodes 13 proteins, 22 tRNAs and 2 rRNAs Heteroplasmy Variable mixture of genetically distinct mitochondria/mtDNAs Properties of mtDNA-encoded traits Maternal inheritance pattern Deficiency in bioenergetic function of organelle Specific mutation in an mtDNA gene

1.线粒体DNA结构基因的突变：有两种疾病被发现有线粒体DNA结构基因的突变，即Leber遗传性视神经病(LHON)及Leigh病。许多线粒体DNA的突变与LHON有关，这些突变均位于结构基因上。在已发现的10多种突变中，有三个点突变被认为与发病最相关，分别位于线粒体DNA第11778、3460及14484位，这些突变改变了保守序列，在非LHON家系中未查到类似突变。线粒体ATP合成障碍可能是LHON的原发性损害。在Leigh病患者的线粒体DNA等8993位有胸腺嘧啶到鸟嘌呤的点突变，这是一个位于高度保守区域的突变，在ATP酶B亚单位的第四个跨膜区造成一处由亮氨酸到精氨酸的突变，突变是异质性的，与疾病的严重程度呈正相关，但只有突变型线粒体 DNA达到一定阈值时才导致Leigh病。体外培养含有95%的突变型线粒体DNA的淋巴细胞内，ATP合成能力仅占正常对照的52%～67%，Leigh病发病中能量减少可能起主要作用

Human Genetic Diseases and Mitochondrial DNA Defects
iActivity: Mitrochondrial DNA and Human Disease 1. Mutations in mtDNA can produce human genetic disorders. Examples: a. Leber’s hereditary optic neuropathy (LHON). Optic nerve degeneration results in complete or partial blindness in mid-life adults. i. LHON is caused by mutations in mtDNA genes for electron transport chain proteins. (These include ND1, ND2, ND4, ND5, ND6, cyt b, COI, COIII, and ATPase 6.) ii. LHON results from defects in the enzymes of oxidative phosphorylation. Without ATP production, the optic nerve dies.

Human mtDNA Disorders Leber’s hereditary optic neuropathy (LHON)
Sudden bilateral blindness 9average age 27 yrs) Most mutations in NADH dehydrogenase gene Maternal transmission to all offspring Many cases appear to be “new” mutations No family history

LHON Leber’s hereditary optic neuropathy 没有一个患者的父亲是患病的；所有女患者的子女都是患病的。

2. 线粒体DNA丢失 b. Kearns-Sayre syndrome produces three types of neuromuscular defects: i. Progressive paralysis of certain eye muscles. ii. Abnormal pigment accumulation on the retina, causing chronic inflammation and degeneration of the retina. iii. Heart disease. iv. Kearns-Sayre syndrome results from deletions in mtDNA. A model for the disorder is that tRNA genes are removed, disrupting mitochondrial translation.

自1991年以来，已有10例病人被报道有线粒体DNA的丢失( depletion)。通过印迹杂交、原位杂交和免疫组化分析，线粒体DNA丢失率可达83 %～98%。Larsson等发现本病患者转录因子A（transcription factor A，TF A）表达减低。线粒体DNA的复制需要DNA聚合酶γ及一个短的RNA引物，这个引物由轻链的转录产物切除而成，可见转录是线粒体DNA复制的先决条件。线粒体TFA表达减少的机制可能是由于翻译过程受损，进入线粒体障碍和TFA的不稳定性。Bodnar 等将线粒体DNA拷贝数减少的细胞脱核后，与无线粒体DNA的癌细胞进行融合，发现融合细胞的线粒体DNA拷贝数恢复，证实线粒体DNA丢失与某些核基因有关。

3.大规模线粒体DNA重排线粒体DNA重排包括缺失（deletion）和重复（duplication），主要见于Kearns-Sayre综合征、慢性进行性眼外肌瘫痪及Pearson综合征。已有120余种线粒体DNA缺失被报道，这些缺失有如下特征：是自发性散在发生的，无家族史；症状随患者年龄增加而恶化；缺失区域一般不包括线粒体DNA的复制起始点。在已发现的各种重排中，“普通缺失”（common deletion）最为常见，缺失区域从线粒体DNA第8482位到13460位。

c. Myoclonic epilepsy and ragged-red fiber disease (MERRF)
c. Myoclonic epilepsy and ragged-red fiber disease (MERRF). Symptoms include: i. Microscopic tissue abnormality, “ragged-red fibers.” ii. Myoclonic seizures (jerking spasms). iii. Ataxia (uncoordinated movement). iv. Accumulation of lactic acid in blood. v. Additional symptoms are sometimes present, including: (1) Dementia. (2) Loss of hearing. (3) Difficulty speaking. (4) Optic atrophy. (5) Involuntary jerking of eyes. (6) Short stature. vi. Mitochondria have abnormal appearance. vii. The cause is a single nucleotide substitution in the lysine tRNA gene. Mitochondrial protein synthesis is affected, and in some way this phenotype is produced.

Human mtDNA Disorders Myoclonic epilepsy and ragged red fiber disease (MERRF) Fibers from proliferation of aberrant mitochondria Mutation in mtDNA tRNA gene

肌阵挛性癫痫合并破碎红纤维(myoclonic epilepsy and ragged red fiber，MERRF)一般被认为是由于线粒体DNA上tRNALys基因上第8344处腺嘌呤到鸟嘌呤的点突变(A8344G)引起。这个突变位于tRNAlys基因TψC 环处，突变的发生机制仍有待查明。Hanna等通过培养患者的成肌细胞的研究发现，线粒体DNA的转录过程正常，蛋白质翻译过程受损。Enriquez等进一步研究认为A8344G引起线粒体内tRNALys的数量减少16%～33%，氨基酸酰化能力减少37%～49%，二者加起来使tRNALys转运赖氨酸的能力减少50%～60%。A8344G并不导致tRNA的成熟过程如CCA加尾等受损，可能由于点突变造成tRNALys的次级或四级结构改变，使tRNALys更易受核酸酶的攻击。　　 1.线粒体tRNA基因突变

在参与蛋白质翻译延长的几个反应中，氨基酰化反应是较为特异的，每个氨基酰tRNA合成酶催化特定的氨基酸与tRN A结合，这个反应过程最易受tRNA变化的影响。特别是在哺乳动物中，tRNA的结构差异大，序列长度、次级结构、延长因子及核糖体的结构不同，互补作用不强。 A 8344G不影响tRNA与氨基酰tRNA合成酶的结合位点，但有可能影响tRNALys的高级结构，妨碍其转运功能，随着蛋白质中赖氨酸残基的增加，蛋白质合成速度也越来越低，在每个赖氨酸密码子或其附近，蛋白质翻译序列终止，不完整的蛋白质释放出来，氨基酰tRNALys的减少是这种现象最可能的原因。这些终止位点可能是Lys-X- Lys结构域，接近于肽链的C末端。

线粒体脑肌病伴乳酸血症(MELAS)，主要由线粒体DNA上的tRNAL eu (UUR)基因第3243处发生胸腺嘧啶到鸟嘌呤的点突变引起，主要证据是：这个突变在不同种族的病人中均可被检测到，正常人无此突变。细胞融合试验证实，细胞的突变型DNA达到90%时可导致线粒体蛋白质翻译功能受抑制，细胞色素C氧化酶活动减弱。单肌纤维分析表明，不整红边纤维中突变型DNA明显比正常肌纤维高，显示突变型DNA在发病机制中起着重要作用。MELAS中有细胞色素C氧化酶活动不正常的小动脉，每一个动脉内不同部位的收缩和舒张功能不均一，微环境的氧供应受到损害，代谢功能失调，最终导致脑血管意外发生。Koga等的细胞融合试验证实，MELAS患者的线粒体内尚未加工的转录产物RNA 19增加，这种产物使线粒体核糖体RNA功能减退，从而抑制了蛋白质翻译。MELAS突变还可导致16 SrRNA转录终止过程受损，终止蛋白与终止序列的结合数量减少一半，16 SrRNA的合成过程异常，影响tRNALeu基因转录产物的正确加工，剩余的终止蛋白可能与D环区域终止序列结合，引起D环区域复制的异常终止。

In most mtDNA disorders, cells of affected individuals have a mix of normal and mutant mitochondria (heteroplasmy). a. Proportions of the two mitochondrial types vary between tissues, and between individuals. b. Severity of disease correlates with the relative amount of mutant mitochondria.

25. Extranuclear Inheritance（cytoplasmic inheritance)

Similar presentations

Presentation on theme: "25. Extranuclear Inheritance（cytoplasmic inheritance)"— Presentation transcript:

Similar presentations

About project

反馈

请登录

Auth with social network:

25. Extranuclear Inheritance（cytoplasmic inheritance)

Similar presentations

Presentation on theme: "25. Extranuclear Inheritance（cytoplasmic inheritance)"— Presentation transcript:

Similar presentations

About project

反馈