染色体的数量和结构的变化课件

1、2022/7/28Variation in Chromosome Number and Structure1Chapter 6Variation in Chromosome Number and Structure2022/7/28Variation in Chromosome Number and Structure2Chromosomes, Agriculture, and Civilization2022/7/28Variation in Chromosome Number and Structure3Chapter OutlineCytological TechniquesPolypl

2、oidy (多倍体)Aneuploidy (非整倍体)Rearrangements of Chromosome Structure2022/7/28Variation in Chromosome Number and Structure4Section 1Cytological TechniquesGeneticists use stains to identify specific chromosomes and to analyze their structures.2022/7/28Variation in Chromosome Number and Structure51. Analy

3、sis of Mitotic ChromosomesPreparation of cells for cytological analysis.2022/7/28Variation in Chromosome Number and Structure6Chromosomes of the incense cedar (Calocedrus decurrens) 北美翠柏stained with aceto-carmine.Until the late 1960s and early 1970s, chromosome spreads were stained with Feulgens rea

4、gent, a purple dye that reacts with the sugar molecules in DNA, or with aceto-carmine (乙酸洋红), a deep red dye.2022/7/28Variation in Chromosome Number and Structure7Chromosomes that have stained with quinacrine show a characteristic pattern of bands.However, because quinacrine is a fluorescent compoun

5、d, the band appear only when the chromosomes are exposed to ultraviolet light.Metaphase chromosomes of the plant Allium carinatum, stained with quinacrine (奎纳克林，阿的平) to reveal Q band.2022/7/28Variation in Chromosome Number and Structure8The most popular of these uses Giemsa stain, a mixture of dyes

6、named after its inventor, Gustav Giemsa.Like quinacrine, Giemsa creates a reproducible pattern of bands on each chromosome.However, the nature of the banding pattern depends on how the chromosomes were prepared prior to staining.G bands2022/7/28Variation in Chromosome Number and Structure9One proced

7、ure, called G banding, gives dark bands that correspond roughly to the bright bands obtained with quinacrine; another procedure, called R banding, gives the reverse patterndark bands that correspond roughly to light G bands.A third procedure, called C banding, stains the region around the centromere

8、 of each chromosome.2022/7/28Variation in Chromosome Number and Structure10Metaphase human chromosomes stained with acridine orange (吖啶橙) to show R banding.Metaphase chromosome of the Melipona rufiventris (卖蜂), M. mondury and M. seminigra fuscopilosa stained to show C banding.2022/7/28Variation in C

9、hromosome Number and Structure112. The Human KaryotypeDiploid human cells contain 46 chromosomes44 autosomes and two sex chromosomes, which are XX in females and XY in males.At mitotic metaphase, each of the chromosomes can be recognized by its size, shape, and banding pattern.The largest autosome i

10、s number 1, and the smallest is number 21.The X chromosome is intermediate in size, and Y chromosome is about the same size as chromosome 22.2022/7/28Variation in Chromosome Number and Structure12蒋有兴 (Joe Hin Tjio，1919-2001) 人类染色体数目的确定者印尼华人徐道觉 (Tao Chiuh Hsu, 1917-2003)低渗法染色体分散技术发现者浙江大学农学院毕业生、谈家桢的学生

11、、美籍华人他们其实都不是真正的中国人！2022/7/28Variation in Chromosome Number and Structure13This chart of chromosome cutouts is called a karyotype (核型).2022/7/28Variation in Chromosome Number and Structure14The karyotype of a human male stained to reveal bands on each of the chromosomes.2022/7/28Variation in Chromoso

12、me Number and Structure153. Cytogenetic Variation: An OverviewThe phenotypes of many organisms are affected by changes in their cells; sometimes even changes in part of a chromosome can be significant.These numerical changes are usually described as variations in the ploidy (倍数) of the organism.2022

13、/7/28Variation in Chromosome Number and Structure16Organisms with complete, or normal, sets of chromosomes are said to be euploid (整倍体).Organisms that carry extra sets of chromosomes are said to be polyploid (多倍体), and the level of polyploidy is described by referring to a basic chromosome number, u

14、sually denoted n.Thus, diploid, with two basic chromosomes sets, have 2n chromosomes; triploids, with three sets, have 3n; tetraploids, with four sets; have 4n; and so forth. 2022/7/28Variation in Chromosome Number and Structure17Organisms in which a particular chromosome, or chromosome segment, is

15、under- or overrepresented are said to be aneuploid (非整倍体).These organisms therefore suffer from a specific genetic imbalance.Mosaic trisomy of chromosome 8. Note eversion (外翻) of lower lip, deep furrows on soles, and CT scan show absence of corpus callosum (胼胝体).2022/7/28Variation in Chromosome Numb

16、er and Structure18The distinction between aneuploidy and polyploidy is that aneuploidy refers to a numerical change in part of the genome, usually just a single chromosome, whereas polyploidy refers to a numerical change in a whole set of chromosomes.Aneuploidy implies a genetic imbalance, but polyp

17、loidy does not.2022/7/28Variation in Chromosome Number and Structure19A piece of one chromosome may be fused to another chromosome, or a segment within a chromosome may be inverted with respect to the rest of that chromosome.These structural changes are called rearrangements.Because rearrangements s

18、egregate irregularly during meiosis, they are often associated with aneuploidy.2022/7/28Variation in Chromosome Number and Structure20Key PointsCytogenetic analysis usually focuses on chromosomes in dividing cells.Dyes such as quinacrine and Giemsa create banding patterns that are useful in identify

19、ing individual chromosomes within a cell.A karyotype shows the photographed chromosomes of a cell arranged for cytogenetic analysis.2022/7/28Variation in Chromosome Number and Structure21Section 2PolyploidyExtra sets of chromosomes in an organism can be affect the organisms appearance and fertility.

20、2022/7/28Variation in Chromosome Number and Structure22Polyploidy, the presence of extra chromosome sets, is fairly common in plants but very rare in animals.One-half of all known plant genera contain polyploid species, and about two-thirds of all grasses are polyploids.Many of these species reprodu

21、ce asexually.In animals, where reproduction is primarily by sexual means, polyploidy is rare, probably because it interferes with the sex-determination mechanism.2022/7/28Variation in Chromosome Number and Structure23One general effect of polyploidy is that cell size is increased, presumably because

22、 there are more chromosomes in the nucleus.Often this increase in size is correlated with an overall increase in the size of the organism.Polyploid species tend to be larger and more robust than their diploid counterparts.2022/7/28Variation in Chromosome Number and Structure24These characteristics h

23、ave a practical significance for human beings, who depend on many polyploid plant species for food.These species tend to produce larger seeds and fruits, and therefore provide greater yields in agriculture.Wheat, coffee, potatoes, bananas, strawberries (草莓), and cotton are all polyploid crop plants.

24、Many ornamental garden plants (观赏植物), including roses, chrysanthemums (菊花), and tulips, are also polyploid.2022/7/28Variation in Chromosome Number and Structure252022/7/28Variation in Chromosome Number and Structure261. Sterile Polyploids (不育性多倍体)Extra sets of chromosomes segregate irregularly in me

25、iosis, leading to grossly unbalanced (that is, aneuploid) gametes.If such gametes unite in fertilization, the resulting zygotes almost always die.2022/7/28Variation in Chromosome Number and Structure27One possibility is that two homologues will pair completely along their length, leaving the third w

26、ithout a partner; this solitary chromosome is called a univalent (单价染色体).2022/7/28Variation in Chromosome Number and Structure28Another possibility is that all three homologous will synapse, forming a trivalent in which each number is partially paired with each of the others.In either case, it is di

27、fficult to predict how the chromosomes will move during anaphase of the first meiotic division.2022/7/28Variation in Chromosome Number and Structure29The more likely event is that two of the homologues will move to one pole, and one homologue will move to the other, yielding gametes with one or two

28、copies of the chromosome.However, all three homologues might move to one pole, producing gametes with zero or three copies of the chromosome.Because this segregational uncertainty applies to each trio of chromosomes in the cell, the total number of chromosomes in a gamete can vary from zero to 3n.20

29、22/7/28Variation in Chromosome Number and Structure30Zygotes formed by fertilization with such gametes are almost certain to die; thus, most triploids are completely sterile.In agriculture and horticulture, this sterility is circumvented by propagating the species asexually.The many methods of asexu

30、al propagation include cultivation from cuttings 插枝 (bananas), grafts 嫁接 (apples), and bulbs 球茎(tulips, 郁金香).In nature, polyploid plants can also reproduce asexually.2022/7/28Variation in Chromosome Number and Structure31One mechanism is apomixis (孤雌生殖), which involves a modified meiosis that produc

31、es unreduced eggs; these eggs then form seeds that germinate into new plants.A plant that reproduces in this way is the dandelion (Taraxacum officinale,蒲公英), a highly successful polyploid weed.2022/7/28Variation in Chromosome Number and Structure322. Fertile Polyploids (可育性多倍体)2022/7/28Variation in

32、Chromosome Number and Structure33Because chromosomes from different species are less likely to interfere with each others segregation during meiosis, polyploids arising from hybridizations between different species have a much greater chance of being fertile than do polyploids arising from duplicati

33、on of chromosomes in a single species.2022/7/28Variation in Chromosome Number and Structure34Polyploids created by hybridization between different species are called allopolyploids (异源多倍体); in these polyploids, the contributing genomes are qualitatively different.Polyploids created by chromosome dup

34、lication within a species are called autopolyploids (同源多倍体); in these polyploids, a single genome has been multiplied to create extra chromosome sets.2022/7/28Variation in Chromosome Number and Structure353. Tissue-Specific Polyploidy and Polyteny (组织特异性多倍体和多线染色体)In some organisms, certain tissues b

35、ecome polyploid during development.This polyplodization is probably a response to the need or multiple copies of each chromosome and the genes it carried.The process that produces such polyploid cells, called endomitosis (核内有丝分裂); followed by separation of the resulting sister chromatids.2022/7/28Va

36、riation in Chromosome Number and Structure36Because there is no accompanying cell division, extra chromosome sets accumulate within a single nucleus.In human liver and kidney, for example, one round of endomitosis produces tetraploid cells.2022/7/28Variation in Chromosome Number and Structure37Somet

37、imes polyploidization occurs without the separation of sister chromatids.In these cases, the duplicated chromosomes pile up next to each other, forming a bundle of strands that are aligned in parallel.The resulting chromosomes are said to be polytene (多线染色体).2022/7/28Variation in Chromosome Number a

38、nd Structure38Polytene chromosomes of Drosophila.2022/7/28Variation in Chromosome Number and Structure39The polytene chromosomes of Drosophia show two additional features:Homologous polytene chromosomes pair. All the centromeres of Drosophila polytene chromosomes congeal into a body called the chrom

39、ocenter (染色中心).2022/7/28Variation in Chromosome Number and Structure40Bridges polytene chromosome maps(Top) Banding pattern of the polytene X chromosome.(Bottom) Detailed view of the left end of the polytene X chromosome showing Bridges system for denoting individual bands.2022/7/28Variation in Chro

40、mosome Number and Structure41Key PointsPolyploids contain extra sets of chromosomes.Many polyploids are sterile because their multiple sets of chromosomes segregate irregularly in meiosis.Polyploids produced by chromosome doubling in interspecific hybrids may be fertile if their constituent genomes

41、segregate independently. In some somatic tissuesfor example, the salivary glands of Drosophila larvaesuccessive rounds of chromosome replication occur without intervening cell divisions and produce large poletene chromosomes that are ideal for cytogenetic analysis.2022/7/28Variation in Chromosome Nu

42、mber and Structure42Section 3AneuploidyThe under- or overrepresentation of a chromosome segment can affect a phenotype.2022/7/28Variation in Chromosome Number and Structure43Aneuploidy describes a numerical change in part of the genome, usually a change in the dosage of a single chromosome.Individua

43、ls that have an extra chromosome, are missing a chromosome, or have a combination of these anomalies are said to be aneuploid.This definition also includes pieces of chromosomes.Thus, an individual in which a chromosome arm has been deleted is also considered to be aneuploid.2022/7/28Variation in Ch

44、romosome Number and Structure44Seed capsules of normal and trisomic (三染色体) Datura tramonium (曼陀罗).Each of the 12 trisomies is shown.最早在植物中被研究原因是在减数分裂过程中染色体的不规则行为造成的！2022/7/28Variation in Chromosome Number and Structure45An organism in which a chromosome, or a piece of a chromosome, is underrepresent

45、ed is referred to as a hypoploid (亚倍体).When a chromosome or chromosome segment is overrepresented, the organism is said to be hyperploid (超倍体).Each of these terms covers a wide range of abnormalities.2022/7/28Variation in Chromosome Number and Structure461. Trisomy in Human BeingsA young girl and 舟舟

46、 with Down syndromeHer karyotype, showing trisome for chromosome 21 (47, XX, +21)2022/7/28Variation in Chromosome Number and Structure472022/7/28Variation in Chromosome Number and Structure482022/7/28Variation in Chromosome Number and Structure49一具Patau syndrome的 37 2/7 周孕龄的男婴，伴有前脑无脑无叶畸形和独眼。 A) 面部特征

47、为额部前倾，长鼻和中央眼裂。B) 眼睑融合及具单鼻孔的长鼻的特写。C) 6指多指畸形。D) 大脑后面观显示脑回不清, 脑半球融合和脑软化。 E) 主动脉异位 (A), 肺部发育不全 (P)。F) Trisomy 13 47, XY, +13 . 2022/7/28Variation in Chromosome Number and Structure50Edward syndrome，47, +18Growth Deficiency, Abnormal skull shape and facial features, Clenched hands, Rocker bottom feet, Ca

48、rdiac and renal abnormalities 2022/7/28Variation in Chromosome Number and Structure51Klinefelter syndrome, 47, XXY or XXY syndrome is a condition in which males have an extra X sex chromosome. Klinefelters syndrome is the most common sex chromosome disorder and the second most common condition cause

49、d by the presence of extra chromosomes. 2022/7/28Variation in Chromosome Number and Structure522. Monosomy Monosomy occurs when one chromosome is missing in an otherwise diploid individual.These individuals have a single X chromosome as well as a diploid complement of autosomes.Phenotypically, they

50、are female, but because their ovaries are rudimentary, they are almost always sterile.45, X individuals are usually short in stature; they have webbed necks, hearing deficiencies, and significant cardiovascular abnormalities.2022/7/28Variation in Chromosome Number and Structure53Turner syndrome马蹄足内翻

51、Henry H. Turner first described the condition in 1938!2022/7/28Variation in Chromosome Number and Structure54Origin of the Turner syndrome karyotype2022/7/28Variation in Chromosome Number and Structure55Why will XX/XO chromosome mosaics in Drosophila produce a Gynandromorphs (两性体).Why should Turner

52、patients, who has the same number of active X chromosomes as normal XX females, show any phenotypic abnormalities at all? Curiously, the cognate of the XO Tuner karyotype in the mouse exhibits no anatomical abnormalities.2022/7/28Variation in Chromosome Number and Structure563. Deletions and Duplica

53、tions of Chromosome SegmentsCri-du-chat syndrome (猫叫综合症)Patients with cri-du-chat syndromeKaryotype of infant with cri-du-chat syndrome, 46, XY (5p-)2022/7/28Variation in Chromosome Number and Structure57Polytene chromosome showingThe normal structure of regions 6 and 7 of the Drosophila X chromosom

54、eA heterozygote with a deletion of region 6F-7C in one of the chromosomes (arrow)An X chromosome showing a reverse tandem duplication of region 6F-7C.In (b) the prominent bands in regions 7A and 7C are present in the upper chromosome, but absent in the lower one, indicating that the lower chromosome

55、 has undergone a deletion.2022/7/28Variation in Chromosome Number and Structure58Effects of duplications for region 16A of the X chromosome on the size of the eyes in Drosophila.2022/7/28Variation in Chromosome Number and Structure59Key PointsIn a trisome, such as Down Syndrome in humans, three copi

56、es of a chromosome are present; in monosomy, such as Turner Syndrome in humans, only one copy of a chromosome is present.Aneuploidy may involve the deletion or duplication of a chromosome segment.2022/7/28Variation in Chromosome Number and Structure60Section 4.Rearrangements of Chromosome StructureA

57、 chromosome may become rearranged internally, or it may become joined to another chromosome.无可奈何花落去，似曾相识燕归来 2022/7/28Variation in Chromosome Number and Structure61自然状况下，染色体的数量和结构是可变的黑腹果蝇有4对染色体黑果蝇有6对染色体随着生物的进化，即使在属内，基因在染色体上也可以重排。重排有2种可能性：倒位：染色体的一个片段的起点反转异位：不同染色体之间位置的交换2022/7/28Variation in Chromosome

58、 Number and Structure621. Inversions (倒位)Inversions occur when a chromosome segment is detached, flipped around 180, and reattached to the rest of the chromosome; as a result, the order of the segments genes is reversed.2022/7/28Variation in Chromosome Number and Structure63倒位的种类Pericentric inversio

59、ns (臂间到位) include the centromere, whereas paracentric (臂内到位) inversions do not.A pericentric inversion changes the size of the chromosome arms because the centromere is included within the inversion.2022/7/28Variation in Chromosome Number and Structure64Possible mechanism of inversion2022/7/28Variation in Chromosome Number and Structure652. Translocations (置换)Translocations occur when a segment from one chromosome is detached and reattached to a different (that is, nonhomologous, 非同源的) chromosome.The genetic significance is that genes from one chromosome are transferred to another