染色体畸变数目改变

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

2、 800 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 characteristics Testicular 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

3、，但睾丸间质细胞不萎缩；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: 1/200 190 cm: 1/30 200 cm: 1/10,Alterations in sex chromosome number,Alterations in autosome number （教材下册P41）,Down Syndrome (trisomy 21 syndr

4、ome),病因：比正常人多了一条21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 retardation Varying degrees of mental retardation Flattened 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 m

5、aternal age increases, the risk of having a baby with Down syndrome increases At age 20 less than 1 in 1000 births results in down syndrome After 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 grow

6、ing, mental retardation, malformed 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, malformat

7、ions of the brain, nervous system, heart defects,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:Alteration

8、s in Chromosome Number,Alterations in chromosome number 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 sper

9、m.,Triploidy,Triploid individuals are born infrequently, and survive for only a short time In 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 g

10、ene regions with similar or repeated sequence Non-disjunction (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 mito

11、sis can produce mosaics, individuals with two types of chromosome 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

12、 the state of having two copies of every single gene-like pairs of 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

13、 others, there are subtle differences between the two copies (they are heterozygous).,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)Tr

14、iploid individuals are often sterile(不育的). Since the chromosomes are unable to pair during 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 i

15、n a Triploid,二体性,Autopolyploidy（同源多倍体） and Allopolyploidy （异源多倍体）,Polyploid plants can result from doubling of chromosomes in a species (autopolyploidy) or from doubling chromosomes number after hybridization (allopolyploidy).,Hybridization and Polyploidy,(1) The hybrid F1 is sterile（不育的）, since the

16、 two sets of chromosomes cannot pair during meiosis. (2) If the chromosome number is doubled, the chromosomes 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

17、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

18、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。