遗传学英文课件：6染色体的数量和结构的变化VIP

1、2020/12/8,Variation in Chromosome Number and Structure,1,Chapter 6Variation in Chromosome Number and Structure,2020/12/8,Variation in Chromosome Number and Structure,2,Chromosomes, Agriculture, and Civilization,2020/12/8,Variation in Chromosome Number and Structure,3,Chapter Outline,Cytological Tech

2、niques Polyploidy (多倍体) Aneuploidy (非整倍体) Rearrangements of Chromosome Structure,2020/12/8,Variation in Chromosome Number and Structure,4,Section 1Cytological Techniques,Geneticists use stains to identify specific chromosomes and to analyze their structures.,2020/12/8,Variation in Chromosome Number

3、and Structure,5,1. Analysis of Mitotic Chromosomes,Preparation of cells for cytological analysis.,2020/12/8,Variation in Chromosome Number and Structure,6,Chromosomes of the incense cedar (Calocedrus decurrens) 北美翠柏stained with aceto-carmine.,Until the late 1960s and early 1970s, chromosome spreads

4、were stained with Feulgens reagent, a purple dye that reacts with the sugar molecules in DNA, or with aceto-carmine (乙酸洋红), a deep red dye.,2020/12/8,Variation in Chromosome Number and Structure,7,Chromosomes that have stained with quinacrine show a characteristic pattern of bands. However, because

5、quinacrine is a fluorescent compound, 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.,2020/12/8,Variation in Chromosome Number and Structure,8,The most popular of the

6、se uses Giemsa stain, a mixture of 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 bands,2020/12/8,Variation

7、in Chromosome Number and Structure,9,One procedure, 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

8、banding, stains the region around the centromere of each chromosome.,2020/12/8,Variation in Chromosome Number and Structure,10,Metaphase 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 fuscopil

9、osa stained to show C banding.,2020/12/8,Variation in Chromosome Number and Structure,11,2. The Human Karyotype,Diploid 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

10、its size, shape, and banding pattern. The largest autosome is 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.,2020/12/8,Variation in Chromosome Number and Structure,12,蒋有兴 (Joe Hin Tjio，1919-2001),人类染色体数目的确定

11、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、美籍华人,他们其实都不是真正的中国人！,2020/12/8,Variation in Chromosome Number and Structure,13,This chart of chromosome cutouts is called a karyotype (核型).,2020/12/8,Variation in Chromosome Number and Structure,14,The karyotype of a human male sta

12、ined to reveal bands on each of the chromosomes.,2020/12/8,Variation in Chromosome Number and Structure,15,3. Cytogenetic Variation: An Overview,The phenotypes of many organisms are affected by changes in their cells; sometimes even changes in part of a chromosome can be significant. These numerical

13、 changes are usually described as variations in the ploidy (倍数) of the organism.,2020/12/8,Variation in Chromosome Number and Structure,16,Organisms 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

14、体), and the level of polyploidy is described 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.,2020/12/8,Variation in Chromosome N

15、umber and Structure,17,Organisms in which a particular chromosome, or chromosome segment, is 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

16、 soles, and CT scan show absence of corpus callosum (胼胝体).,2020/12/8,Variation in Chromosome Number and Structure,18,The 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

17、 a numerical change in a whole set of chromosomes. Aneuploidy implies a genetic imbalance, but polyploidy does not.,2020/12/8,Variation in Chromosome Number and Structure,19,A piece of one chromosome may be fused to another chromosome, or a segment within a chromosome may be inverted with respect to

18、 the rest of that chromosome. These structural changes are called rearrangements. Because rearrangements segregate irregularly during meiosis, they are often associated with aneuploidy.,2020/12/8,Variation in Chromosome Number and Structure,20,Key Points,Cytogenetic analysis usually focuses on chrom

19、osomes in dividing cells. Dyes such as quinacrine and Giemsa create banding patterns that are useful in identifying individual chromosomes within a cell. A karyotype shows the photographed chromosomes of a cell arranged for cytogenetic analysis.,2020/12/8,Variation in Chromosome Number and Structure

20、,21,Section 2Polyploidy,Extra sets of chromosomes in an organism can be affect the organisms appearance and fertility.,2020/12/8,Variation in Chromosome Number and Structure,22,Polyploidy, the presence of extra chromosome sets, is fairly common in plants but very rare in animals. One-half of all kno

21、wn plant genera contain polyploid species, and about two-thirds of all grasses are polyploids. 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.,2020/12/8,Va

22、riation in Chromosome Number and Structure,23,One general effect of polyploidy is that cell size is increased, 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 la

23、rger and more robust than their diploid counterparts.,2020/12/8,Variation in Chromosome Number and Structure,24,These 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 theref

24、ore provide greater yields in agriculture. Wheat, coffee, potatoes, bananas, strawberries (草莓), and cotton are all polyploid crop plants. Many ornamental garden plants (观赏植物), including roses, chrysanthemums (菊花), and tulips, are also polyploid.,2020/12/8,Variation in Chromosome Number and Structure

25、,25,2020/12/8,Variation in Chromosome Number and Structure,26,1. Sterile Polyploids (不育性多倍体),Extra sets of chromosomes segregate irregularly in meiosis, leading to grossly unbalanced (that is, aneuploid) gametes. If such gametes unite in fertilization, the resulting zygotes almost always die.,2020/1

26、2/8,Variation in Chromosome Number and Structure,27,One possibility is that two homologues will pair completely along their length, leaving the third without a partner; this solitary chromosome is called a univalent (单价染色体).,2020/12/8,Variation in Chromosome Number and Structure,28,Another possibili

27、ty 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 difficult to predict how the chromosomes will move during anaphase of the first meiotic division.,2020/12/8,Variation in Chromosome Number and Str

28、ucture,29,The 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 copies of the chromosome. However, all three homologues might move to one pole, producing gametes with zero or three copies of the chromosom

29、e. 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.,2020/12/8,Variation in Chromosome Number and Structure,30,Zygotes formed by fertilization with such gametes are almost certain to die; thus

30、, most triploids are completely sterile. In agriculture and horticulture, this sterility is circumvented by propagating the species asexually. The many methods of asexual propagation include cultivation from cuttings 插枝 (bananas), grafts 嫁接 (apples), and bulbs 球茎(tulips, 郁金香). In nature, polyploid p

31、lants can also reproduce asexually.,2020/12/8,Variation in Chromosome Number and Structure,31,One mechanism is apomixis (孤雌生殖), which involves a modified meiosis that produces unreduced eggs; these eggs then form seeds that germinate into new plants. A plant that reproduces in this way is the dandel

32、ion (Taraxacum officinale,蒲公英), a highly successful polyploid weed.,2020/12/8,Variation in Chromosome Number and Structure,32,2. Fertile Polyploids (可育性多倍体),2020/12/8,Variation in Chromosome Number and Structure,33,Because chromosomes from different species are less likely to interfere with each oth

33、ers segregation during meiosis, polyploids arising from hybridizations between different species have a much greater chance of being fertile than do polyploids arising from duplication of chromosomes in a single species.,2020/12/8,Variation in Chromosome Number and Structure,34,Polyploids created by

34、 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 duplication within a species are called autopolyploids (同源多倍体); in these polyploids, a single genome has been multip

35、lied to create extra chromosome sets.,2020/12/8,Variation in Chromosome Number and Structure,35,3. Tissue-Specific Polyploidy and Polyteny (组织特异性多倍体和多线染色体),In some organisms, certain tissues become polyploid during development. This polyplodization is probably a response to the need or multiple copi

36、es 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.,2020/12/8,Variation in Chromosome Number and Structure,36,Because there is no accompanying cell division, extra chro

37、mosome sets accumulate within a single nucleus. In human liver and kidney, for example, one round of endomitosis produces tetraploid cells.,2020/12/8,Variation in Chromosome Number and Structure,37,Sometimes polyploidization occurs without the separation of sister chromatids. In these cases, the dup

38、licated 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).,2020/12/8,Variation in Chromosome Number and Structure,38,Polytene chromosomes of Drosophila.,2020/12/8,Variation in Chromosome Number

39、and Structure,39,The 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 chromocenter (染色中心).,2020/12/8,Variation in Chromosome Number and Structure,40,Bridges poly

40、tene 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.,2020/12/8,Variation in Chromosome Number and Structure,41,Key Points,Polyploids contain extra sets of chr

41、omosomes. 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 segregate independently. In some somatic tissuesfor example, the salivary

42、 glands of Drosophila larvaesuccessive rounds of chromosome replication occur without intervening cell divisions and produce large poletene chromosomes that are ideal for cytogenetic analysis.,2020/12/8,Variation in Chromosome Number and Structure,42,Section 3Aneuploidy,The under- or overrepresentat

43、ion of a chromosome segment can affect a phenotype.,2020/12/8,Variation in Chromosome Number and Structure,43,Aneuploidy describes a numerical change in part of the genome, usually a change in the dosage of a single chromosome. Individuals that have an extra chromosome, are missing a chromosome, or

44、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.,2020/12/8,Variation in Chromosome Number and Structure,44,Seed capsules of normal an

45、d 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！,2020/12/8,Variation in Chromosome Number and Structure,45,An organism in which a chromosome, or a piece of a chromosome, is underrepresented is referred to as a hypoploid (亚倍体). When a chr

46、omosome 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.,2020/12/8,Variation in Chromosome Number and Structure,46,1. Trisomy in Human Beings,A young girl and 舟舟 with Down syndrome Her karyotype, showing

47、trisome for chromosome 21 (47, XX, +21),2020/12/8,Variation in Chromosome Number and Structure,47,2020/12/8,Variation in Chromosome Number and Structure,48,2020/12/8,Variation in Chromosome Number and Structure,49,一具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

48、。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 .,2020/12/8,Variation in Chromosome Number and Structure,50,Edward syndrome，47, +18 Growth Deficiency, Abnormal skull shape and facial features, Clenched hands, Rocker bottom feet, Cardiac and renal abnormalitie

49、s,2020/12/8,Variation in Chromosome Number and Structure,51,Klinefelter 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 caused by the presence of extr

50、a chromosomes.,2020/12/8,Variation in Chromosome Number and Structure,52,2. 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 are female, but beca

51、use 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.,2020/12/8,Variation in Chromosome Number and Structure,53,Turner syndrome,马蹄足内翻,Henry H. Turn

52、er first described the condition in 1938!,2020/12/8,Variation in Chromosome Number and Structure,54,Origin of the Turner syndrome karyotype,2020/12/8,Variation in Chromosome Number and Structure,55,Why will XX/XO chromosome mosaics in Drosophila produce a Gynandromorphs (两性体). Why should Turner pati

53、ents, 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.,2020/12/8,Variation in Chromosome Number and Structure,56,3. Deletions and Duplica

54、tions of Chromosome Segments,Cri-du-chat syndrome (猫叫综合症) Patients with cri-du-chat syndrome Karyotype of infant with cri-du-chat syndrome, 46, XY (5p-),2020/12/8,Variation in Chromosome Number and Structure,57,Polytene chromosome showing The normal structure of regions 6 and 7 of the Drosophila X c

55、hromosome A 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

56、 chromosome has undergone a deletion.,2020/12/8,Variation in Chromosome Number and Structure,58,Effects of duplications for region 16A of the X chromosome on the size of the eyes in Drosophila.,2020/12/8,Variation in Chromosome Number and Structure,59,Key Points,In a trisome, such as Down Syndrome i

57、n humans, three copies 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.,2020/12/8,Variation in Chromosome Number and Structure,60,Section 4.Rearrangements

58、 of Chromosome Structure,A 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,2020/12/8,Variation in Chromosome Number and Structure,61,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

59、置的交换,2020/12/8,Variation in Chromosome Number and Structure,62,1. 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.,2020/12/8,Variation in Chromosome Number and Structure,63,倒位的种类,Pericentric inversions (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.,2020/12/8,Variation in Chromosome Number and Structu