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1、Alterations in sex chromosome number（教材上册p142）,Turner Syndrome(45,X),1 in 2500 liveborn females,Characteristics,Short stature wide nipples,性腺发育不全综合症,身材矮，蹼颈，肘外翻，原发性闭经，生殖器幼稚，索状性腺（结缔组织，无卵泡）。成因：早期卵裂过程中染色体不分离。,多数有生育能力，少数卵巢功能异常，2/3伴有轻度智力低下，并有患精神病的倾向。,Two of the three X chromosomes are inactivated.,1 in 80
2、0 males,Tall with disproportionately long arms/legs,Klinefelter syndrome(47,XXY)（克氏综合症）,1 in 100 mentally retarded males,1 in 10 infertile males,Poorly developed secondary sex characteristicsTesticular dysgenesis,Alterations in sex chromosome number,先天性睾丸发育不全综合征,女性体态，有女性化乳房，胡须少，皮肤较嫩；睾丸小而硬，无精子，但睾丸间质细
3、胞不萎缩；智力低下。,1 in 750 1500 males,Tall stature,XYY syndrome(47,XYY),1 in 30 male prison populations,Predisposition to violent,criminal behavior,180 cm:1/200190 cm:1/30200 cm:1/10,Alterations in sex chromosome number,Alterations in autosome number（教材下册P41）,Down Syndrome(trisomy 21 syndrome),病因：比正常人多了一条2
4、1号常染色体唐氏综合症：智力低下，身体发育缓慢。常表现为特殊的面容,较敏感和快乐,寿命短。,Characteristics,Growth retardationVarying degrees of mental retardationFlattened face Upward slanting of the eyes with epicanthal folds,1 in 600 800 newborns,Down Syndrome(trisomy 21 syndrome),皮肤折痕,Down Syndrome and Maternal Age,As maternal age increases
5、,the risk of having a baby with Down syndrome increasesAt age 20 less than 1 in 1000 births results in down syndromeAfter age 40,greater than 1 in 100 births results in Down syndrome,如果经适当教育，唐氏症患者依然可以有很好的表現,Trisomy 18:Edwards Syndrome,(47,+18)small at birth,very slow growing,mental retardation,malfo
6、rmed feet,heart malformations.For unknown reasons,80%of live born trisomy 18 babies are female.,Edwards Syndrome(trisomy 18 syndrome),Trisomy 13:Patau Syndrome,(47,+13)Facial malformations,eye defects,extra fingers or toes,feet with protruding heels,malformations of the brain,nervous system,heart de
7、fects,Frequencies of Trisomies in Spontaneous Abortions,Some Chromosomes are rarely seen as trisomies in abortuses(1,5,11,17,19)Other chromosomes occur frequently as trisomies(16)The reasons for these differences are not clear.,Aneuploidy:Alterations in Chromosome Number,Alterations in chromosome nu
8、mber can cause polyploidy of cells.The occurrence of an entire extra set of chromosomes produces triploid cells.This can be caused by a nuclear duplication with no cell division in meiosis,or more commonly by fertilization of one ovum by two sperm.,Triploidy,Triploid individuals are born infrequentl
9、y,and survive for only a short timeIn this circumstance,all of the proper genetic material is present,only there are three copies of each chromosome rather than two.,Causes of Genetic Abnormalities,Unequal crossing over can cause changes in gene regions with similar or repeated sequenceNon-disjuncti
10、on(不分开)can cause changes in chromosome number(aneuploidy，非整倍体),Meiosis Nondisjunction,Nondisjunction can produce different outcomes depending on whether it occurs in meiosis 1 or meiosis 2,Mitotic Nondisjunction,Nondisjunction during mitosis can produce mosaics,individuals with two types of chromoso
11、me arrangements.,Chromosomal Lagging,Chromosomal lagging can result in the loss of one(or more)chromosomes,either in meiosis or mitosis.,Alterations in Chromosome Number in plant,Chromosome complement:染色体组（下册P26）,Diploidy,Diploidy is the state of having two copies of every single gene-like pairs of
12、shoes.Humans,and many of the organisms with which we are familiar(flies,zebras,potatoes),are diploid.We have two copies of every gene in our bodies.For many genes,these copies are identical matches(they are homozygous).For others,there are subtle differences between the two copies(they are heterozyg
13、ous).,Diploidy,Not all organisms are diploid as adults,some are haploid.For sexual reproduction to occur,there must be both a diploid and a haploid phase of the life cycle.,Polyploidy(多倍体)and Speciation(物种形成),(1)Triploid individuals are often sterile(不育的).Since the chromosomes are unable to pair dur
14、ing meiosis,unequal segregation often results(2)Tetraploid individuals are less likely to be sterile.(3)In plants,polyploid conditions are not uncommon,and may be the source of many new species.,.,Meiosis in a Triploid,二体性,Autopolyploidy（同源多倍体）and Allopolyploidy（异源多倍体）,Polyploid plants can result fr
15、om doubling of chromosomes in a species(autopolyploidy)or from doubling chromosomes number after hybridization(allopolyploidy).,Hybridizationand Polyploidy,(1)The hybrid F1 is sterile（不育的）,since the two sets of chromosomes cannot pair during meiosis.(2)If the chromosome number is doubled,the chromos
16、omes each have a homolog with which to pair,and the polyploid is fertile（可育的）.,(萝卜甘蓝)F1未减数配子融合,普通小麦(Triticum aestivum)的起源,三倍体无子西瓜的培育过程,父本,母本,授粉,四倍体,二倍体,有子西瓜,种下去,三倍体植株,花粉刺激,（提供生长素）,普通西瓜植株,无子西瓜,八倍体小黑麦的人工合成与应用(鲍文奎等),秋水仙素处理萌发的种子或幼苗,四倍体小黑麦（不育）,（耐贫瘠的土壤和寒冷的气候，面粉白，蛋白质含量高，产量高),二倍体黑麦,六倍体普通小麦,八倍体小黑麦（8n）,同源多倍体的
17、特征,(1)形态特征：表现大型性 随染色体组数的增加，同源多倍体的细胞、细胞核、营养器官、生殖器官等多数有增大的趋势，表现为叶片肥厚、宽大、长，茎杆粗壮，花、花粉粒、果实、种子、气孔等器官组织较大，产量较二倍体高。(2)生理生化代谢的改变：表现基因的剂量效应 同源多倍体的生化反应与代谢活动加强，许多性状的表现更强。如：大麦同源四倍体籽粒蛋白质含量比二倍体原种增加10-12；玉米同源四倍体籽粒胡萝卜素含量比二倍体原种增加43。,(1)异源多倍体是广泛存在的。被子植物纲中有30-35是异源多倍体；禾本科植物有70是异源多倍体，如：小麦、燕麦、甘蔗等；其它农作物；烟草、甘蓝型油菜、棉花等也是异源多倍
18、体。(2)自然界中能正常繁殖的异源多倍体物种几乎都是偶倍数。因为细胞内的染色体组成对存在，同源染色体能正常配对形成二价体，并分配到配子中去，因而其遗传表现与二倍体相似。,异源多倍体存在的广泛性,课堂讨论：1染色体结构变异修复机制；人类染色体畸变分析与遗传病？2染色体数目变异对动、植物个体的影响的异同。作业与思考题：1.本章的基本概念和名词术语。2.阅读全书或其它参考资料，思考造成染色体结构变异的机制（或原因）有哪些？3.选择教材及主要参考书上的部分计算题和综合分析题。4结合遗传学实验，总结诱变的细胞学特征。5主要染色体畸变类型的遗传分析。,6缺失、重复和倒位在减数第一分裂前期染色体形态上所表现的相拟性，镜检时怎样区别它们？7微缺失和基因突变有类似的表现型，怎样对其进行正确的判定？8倒位杂合体和易位杂合体都能产生不育配子，为什么称半不育是易位杂合体的突出特点？9缺失、倒位和易位都能影响到重组率，在影响的机制上它们之间有何不同？10比较染色体基组与染色体组型各自的含义。11同源多倍体和异源多倍体是怎样形成的？12超倍体有哪些类型？它们各自的遗传特点和实践意义如何？13亚倍体有哪些类型？它们各自的遗传特点和实践意义如何？,
