1、2023-2-15Variation in Chromosome Number and Structure1Chapter 6Variation in Chromosome Number and Structure2023-2-15Variation in Chromosome Number and Structure2Chromosomes,Agriculture,and Civilization2023-2-15Variation in Chromosome Number and Structure3Chapter OutlineCytological TechniquesPolyploi
2、dy(多倍体多倍体)Aneuploidy(非整倍体非整倍体)Rearrangements of Chromosome Structure2023-2-15Variation in Chromosome Number and Structure4Section 1Cytological TechniquesGeneticists use stains to identify specific chromosomes and to analyze their structures.2023-2-15Variation in Chromosome Number and Structure51.Ana
3、lysis of Mitotic ChromosomesPreparation of cells for cytological analysis.2023-2-15Variation in Chromosome Number and Structure6Chromosomes of the incense cedar(Calocedrus decurrens)北美翠柏北美翠柏stained with aceto-carmine.Until the late 1960s and early 1970s,chromosome spreads were stained with Feulgens
4、reagent,a purple dye that reacts with the sugar molecules in DNA,or with aceto-carmine(乙乙酸洋红酸洋红),a deep red dye.2023-2-15Variation in Chromosome Number and Structure7Chromosomes that have stained with quinacrine show a characteristic pattern of bands.However,because quinacrine is a fluorescent compo
5、und,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，奎纳克林，阿的平阿的平)to reveal Q band.2023-2-15Variation in Chromosome Number and Structure8The most popular of these uses Giemsa stain,a mixture of
6、dyes 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 bands2023-2-15Variation in Chromosome Number and Structure9One proc
7、edure,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 of e
8、ach chromosome.2023-2-15Variation in Chromosome Number and Structure10Metaphase human chromosomes stained with acridine orange(吖啶橙吖啶橙)to show R banding.Metaphase chromosome of the Melipona rufiventris(卖卖蜂蜂),M.mondury and M.seminigra fuscopilosa stained to show C banding.2023-2-15Variation in Chromos
9、ome 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 is number 1,
10、and the smallest is number 21.The X chromosome is intermediate in size,and Y chromosome is about the same size as chromosome 22.2023-2-15Variation in Chromosome Number and Structure12蒋有兴蒋有兴(Joe Hin Tjio，1919-2001)人类染色体数目的确定者人类染色体数目的确定者印尼华人印尼华人徐道觉徐道觉(Tao Chiuh Hsu,1917-2003)低渗法染色体分散技术发现者低渗法染色体分散技术发现者
11、浙江大学农学院毕业生、谈家浙江大学农学院毕业生、谈家桢的学生、美籍华人桢的学生、美籍华人他们其实都不是真正的中国人！他们其实都不是真正的中国人！2023-2-15Variation in Chromosome Number and Structure13This chart of chromosome cutouts is called a karyotype(核型核型).2023-2-15Variation in Chromosome Number and Structure14The karyotype of a human male stained to reveal bands on
12、each of the chromosomes.2023-2-15Variation in Chromosome 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
13、 variations in the ploidy(倍数倍数)of the organism.2023-2-15Variation in Chromosome Number and Structure16Organisms with complete,or normal,sets of chromosomes are said to be euploid(整倍体整倍体).Organisms that carry extra sets of chromosomes are said to be polyploid(多倍多倍体体),and the level of polyploidy is de
14、scribed by referring to a basic chromosome number,usually 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.2023-2-15Variation in Chromosome Number and Structure17Organisms in which a particula
15、r chromosome,or chromosome segment,is under-or overrepresented are said to be aneuploid(非非整倍体整倍体).These organisms therefore suffer from a specific genetic imbalance.Mosaic trisomy of chromosome 8.Note eversion(外翻外翻)of lower lip,deep furrows on soles,and CT scan show absence of corpus callosum(胼胝体胼胝体
16、).2023-2-15Variation in Chromosome Number 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 i
17、mplies a genetic imbalance,but polyploidy does not.2023-2-15Variation 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 rear
18、rangements.Because rearrangements segregate irregularly during meiosis,they are often associated with aneuploidy.2023-2-15Variation in Chromosome Number and Structure20Key PointsCytogenetic analysis usually focuses on chromosomes in dividing cells.Dyes such as quinacrine and Giemsa create banding pa
19、tterns that are useful in identifying individual chromosomes within a cell.A karyotype shows the photographed chromosomes of a cell arranged for cytogenetic analysis.2023-2-15Variation in Chromosome Number and Structure21Section 2PolyploidyExtra sets of chromosomes in an organism can be affect the o
20、rganisms appearance and fertility.2023-2-15Variation 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 polyploid
21、s.Many of these species reproduce asexually.In animals,where reproduction is primarily by sexual means,polyploidy is rare,probably because it interferes with the sex-determination mechanism.2023-2-15Variation in Chromosome Number and Structure23One general effect of polyploidy is that cell size is i
22、ncreased,presumably because 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.2023-2-15Variation in Chromosome Number and Structu
23、re24These characteristics have 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(草莓草莓),and cotton are all p
24、olyploid crop plants.Many ornamental garden plants(观赏植物观赏植物),including roses,chrysanthemums(菊花菊花),and tulips,are also polyploid.2023-2-15Variation in Chromosome Number and Structure252023-2-15Variation in Chromosome Number and Structure261.Sterile Polyploids(不育性多倍体不育性多倍体)Extra sets of chromosomes se
25、gregate irregularly in meiosis,leading to grossly unbalanced(that is,aneuploid)gametes.If such gametes unite in fertilization,the resulting zygotes almost always die.2023-2-15Variation in Chromosome Number and Structure27One possibility is that two homologues will pair completely along their length,
26、leaving the third without a partner;this solitary chromosome is called a univalent(单价染色单价染色体体).2023-2-15Variation 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
27、either case,it is difficult to predict how the chromosomes will move during anaphase of the first meiotic division.2023-2-15Variation 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 gamete
28、s with one or two 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 fro
29、m zero to 3n.2023-2-15Variation 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 meth
30、ods of asexual propagation include cultivation from cuttings 插枝插枝(bananas),grafts 嫁接嫁接(apples),and bulbs 球球茎茎(tulips,郁金香郁金香).In nature,polyploid plants can also reproduce asexually.2023-2-15Variation in Chromosome Number and Structure31 One mechanism is apomixis(孤雌生殖孤雌生殖),which involves a modified m
31、eiosis that produces unreduced eggs;these eggs then form seeds that germinate into new plants.A plant that reproduces in this way is the dandelion(Taraxacum officinale,蒲公英蒲公英),a highly successful polyploid weed.2023-2-15Variation in Chromosome Number and Structure322.Fertile Polyploids(可育性多倍体可育性多倍体)
32、2023-2-15Variation in 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 a
33、rising from duplication of chromosomes in a single species.2023-2-15Variation in Chromosome Number and Structure34Polyploids created by hybridization between different species are called allopolyploids(异异源多倍体源多倍体);in these polyploids,the contributing genomes are qualitatively different.Polyploids cr
34、eated by chromosome duplication within a species are called autopolyploids(同源多倍体同源多倍体);in these polyploids,a single genome has been multiplied to create extra chromosome sets.2023-2-15Variation in Chromosome Number and Structure353.Tissue-Specific Polyploidy and Polyteny(组织特异性多倍体和多线组织特异性多倍体和多线染色体染色体
35、)In some organisms,certain tissues become 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(核内有丝分裂核内有丝分裂);followed by separation of the
36、resulting sister chromatids.2023-2-15Variation 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.2023-2-15Variation in Ch
37、romosome Number and Structure37Sometimes 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(多线染色体多线染色体).202
38、3-2-15Variation in Chromosome Number and Structure38Polytene chromosomes of Drosophila.2023-2-15Variation in Chromosome Number and Structure39 The polytene chromosomes of Drosophia show two additional features:1.Homologous polytene chromosomes pair.2.All the centromeres of Drosophila polytene chromo
39、somes congeal into a body called the chromocenter(染色中心染色中心).2023-2-15Variation 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
40、individual bands.2023-2-15Variation in Chromosome 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 m
41、ay be fertile if their constituent genomes 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 ana
42、lysis.2023-2-15Variation in Chromosome Number and Structure42Section 3AneuploidyThe under-or overrepresentation of a chromosome segment can affect a phenotype.2023-2-15Variation in Chromosome Number and Structure43Aneuploidy describes a numerical change in part of the genome,usually a change in the
43、dosage of a single chromosome.Individuals 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 b
44、e aneuploid.2023-2-15Variation in Chromosome Number and Structure44Seed capsules of normal and trisomic(三染色体三染色体)Datura tramonium(曼陀罗曼陀罗).Each of the 12 trisomies is shown.最早在植物中被研究最早在植物中被研究原因是在减数分裂过程原因是在减数分裂过程中染色体的不规则行为中染色体的不规则行为造成的！造成的！2023-2-15Variation in Chromosome Number and Structure45An orga
45、nism in which a chromosome,or a piece of a chromosome,is underrepresented is referred to as a hypoploid(亚倍体亚倍体).When a chromosome or chromosome segment is overrepresented,the organism is said to be hyperploid(超倍体超倍体).Each of these terms covers a wide range of abnormalities.2023-2-15Variation in Chro
46、mosome Number and Structure461.Trisomy in Human Beingsa.A young girl and 舟舟舟舟 with Down syndromeb.Her karyotype,showing trisome for chromosome 21(47,XX,+21)2023-2-15Variation in Chromosome Number and Structure472023-2-15Variation in Chromosome Number and Structure482023-2-15Variation in Chromosome N
47、umber and Structure49 一具一具Patau syndrome的的 37 2/7 周孕龄的男婴，周孕龄的男婴，伴有前脑无脑无叶畸形伴有前脑无脑无叶畸形和独眼。和独眼。A)面部特征为面部特征为额部前倾，长鼻和中央额部前倾，长鼻和中央眼裂。眼裂。B)眼睑融合及具眼睑融合及具单鼻孔的长鼻的特写。单鼻孔的长鼻的特写。C)6指多指畸形。指多指畸形。D)大大脑后面观显示脑回不清脑后面观显示脑回不清,脑半球融合和脑软化。脑半球融合和脑软化。E)主动脉异位主动脉异位(A),肺部肺部发育不全发育不全(P)。F)Trisomy 13 47,XY,+13.2023-2-15Variation in
48、 Chromosome Number and Structure50S Edward syndrome，47,+18 Growth Deficiency,Abnormal skull shape and facial features,Clenched hands,Rocker bottom feet,Cardiac and renal abnormalities 2023-2-15Variation in Chromosome Number and Structure51Klinefelter syndrome,47,XXY or XXY syndrome is a condition in
49、 which males have an extra X sex chromosome.Klinefelters syndrome is the most common sex chromosome disorder and the second most common condition caused by the presence of extra chromosomes.2023-2-15Variation in Chromosome Number and Structure522.Monosomy Monosomy occurs when one chromosome is missi
50、ng in an otherwise diploid individual.These individuals have a single X chromosome as well as a diploid complement of autosomes.Phenotypically,they 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
