页数：45页文件大小：976.5 KB来源： 分子生物学基因Geneppt课件
本课件为《分子生物学》第2章从基因到基因组（From Genes to Genomes），依据 Gene VII 编排，讲解本章核心概念与分子机制，配逐页图示与文字版。
Chapter 2 From Genes to Genomes
2.1 Introduction We can think about mapping genes and genomes at several levels of resolution:A genetic (or linkage) map identifies the distance between mutations in terms of recombination frequencies. A linkage map can also be constructed by measuring recombination between sites in genomic DNA. A restriction map is constructed by cleaving DNA into fragments with restriction enzymes and measuring the distances between the sites of cleavage. The ultimate map is to determine the sequence of the DNA. From the sequence, we can identify genes and the distances between them.
2.1 Introduction2.2 The nature of interrupted genes2.3 Organization of interrupted genes may be conserved2.4 Exon sequences are conserved but introns vary2.5 Genes can be isolated by the conserv at ion of exons2.6 Genes show a wide distribution of sizes2.7 Some DNA sequences code for more than one protein2.8 How did interrupted genes evolve?
bp is an abbrevi at ion for base pairs; distance along DNA is measured in bp.
Figure 2.1 DNA can be cleaved by restriction enzymes into fragments that can be separated by gel electrophoresis.
Figure 2.2 Double digests define the cleavage positions of one enzyme with regard to the other.
Figure 2.3 A restriction map can be constructed by relating the A-fragments and B-fragments through the overlaps seen with double digest fragments.
Figure 2.4 When restriction fragments are identified by their possession of a labeled end, each fragment directly shows the distance of a cutting site from the end. Successive fragments increase in length by the distance between adjacent restriction sites.
Figure 2.5 A restriction map is a linear sequence of sites separated by defined distances on DNA. The map identifies the sites cleaved by enzymes A and B, as defined by the individual fragments produced by the single and double digests.
Figure 2.6 A point mutation that affects a restriction site is detected by a difference in restriction fragments. 2.3 How variable are individual genomes?.
Four alleles for a restriction marker are found in all possible pairwise combin at ions, and segregate independently at each gener at ion. Photograph kindly provided by Ray White.
2.3 How variable are individual genomes?Figure 2.7 Restriction site polymorphisms are inherited according to Mendeli an rules.
Figure 2.8 A restriction polymorphism can be used as a genetic marker to measure recombination distance from a phenotypic marker (such as eye color). The figure simplifies the situ at ion by showing only the DNA bands corresponding to the allele of the other genome in a diploid.2.3 How variable are individual genomes?.
Figure 2.9 If a restriction marker is associated with a phenotypic characteristic, the restriction site must be located near the gene responsible for the phenotype.2.3 How variable are individual genomes?The mutation changing the band that is common in normal people into the band that is common in patients is very closely linked to the disease gene.
2.3 How variable are individual genomes?The mutation changing the band that is common in normal people into the band that is common in patients is very closely linked to the disease gene.
Figure 2.9 If a restriction marker is associated with a phenotypic characteristic, the restriction site must be located near the gene responsible for the phenotype.2.3 How variable are individual genomes?The mutation changing the band that is common in normal people into the band that is common in patients is very closely linked to the disease gene.
2.3 How variable are individual genomes?The mutation changing the band that is common in normal people into the band that is common in patients is very closely linked to the disease gene.
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Figure 2.10 Interrupted genes are expressed via a precursor RNA. Introns are removed when the exons are spliced together. The mRNA has only the sequences of the exons.
Figure 2.11 Comparison of the restriction maps of cDNA and genomic DNA for mouse b-globin shows that the gene has two introns that are not present in the cDNA. The exons can be aligned exactly between cDNA and gene.
Figure 2.12 An intron is a sequence present in the gene but absent from the mRNA (here shown in terms of the cDNA sequence). The reading frame is indicated by the alternating open and shaded blocks; note that all three possible reading frames are blocked by termination codons in the intron.
Figure 2.13 All functional globin genes have an interrupted structure with three exons. The lengths indicated in the figure apply to the mammalian b-globin genes.
Figure 2.14 Mammalian genes for DHFR have the same relative organization of rather short exons and very long introns, but vary extensively in the lengths of corresponding introns.
Figure 2.15 The sequences of the mouse amajand aminglob in genes are closely related in coding regions, but differ in the flanking regions and large intron. Data kindly provided by Philip Leder.
Zoo blot describes the use of Southern blotting to test the ability of a DNA probe from one species to hybridize with the DNA from the genomes of a variety of other species.
Figure 2.16 Chromosome walking is accomplished by successive hybridiz at ions between overlapping genomic clones.
Figure 2.17 A zoo blot with a probe from the human Y chromosomal gene zfy identifies cross-hybridizing fragments on the sex chromosomes of other mammals and birds. There is one reacting fragment on the Y chromosome and another on the X chromosome. Data kindly provided by Dabid Page.
Figure 2.18 The gene involved in Duchenne muscular dystrophy has been tracked down by chromosome mapping and walking to a region in which deletions can be identified with the occurrence of the disease.
Figure 2.19 The Duchene muscular dystrophy gene has been characterized by zoo blotting, cDNA hybridization, genomic hybridization, and identific at ion of the protein.
Figure 2.20 A special splicing vector is used for exon trapping. If an exon is present in the genomic fragment, its sequence will be recovered in the cytoplasmic RNA, but if the genomic fragment consists solely of an intron,.
Figure 2.21 Exons coding for proteins are usually short.
Figure 2.22 Introns in vertebrate genes range from very short to very long.
Figure 2.23 Most genes are uninterrupted in yeast, but most genes are interrupted in flies and mammals. (Uninterrupted genes have only 1 exon, and are tot a led in the left most column.).
Figure 2.24 Yeast genes are small, but genes in flies and mammals have a dispersed distribution extending to very large sizes.
Figure 2.25 Two proteins can be generated from a single gene by starting (or terminating) expression at different points.
Figure 2.26 Two genes may share the same sequence by reading the DNA in different frames.
Figure 2.27 Alternative splicing uses the same pre-mRNA to generate mRNAs that have different combin-ations of exons.
Figure 2.28 Alternative splicing generates the aand bvariants of tropon in T.
Figure 2.29 Immunoglobulin light chains and heavy chains are coded by genes whose structures (in their expressed forms) correspond with the distinct domains in the protein. Each protein domain corresponds to an exon; introns are num be red 1-5.2.10 How did interrupted genes evolve?.
Figure 2.30 The LDL receptor gene consists of 18 exons, some of which are related to EGF precursor and some to the C9 blood complement gene. Triangles mark the positions of introns. Only some of the introns in the region related to EGF precursor are identical in position to those in the EGF gene.2.10 How did interrupted genes evolve?.
Figure 2.20 A special splicing vector is used for exon trapping. If an exon is present in the genomic fragment, its sequence will be recovered in the cytoplasmic RNA, but if the genomic fragment consists solely of an intron,2.10 How did interrupted genes evolve?.
Figure 2.20 A special splicing vector is used for exon trapping. If an exon is present in the genomic fragment, its sequence will be recovered in the cytoplasmic RNA, but if the genomic fragment consists solely of an intron,2.10 How did interrupted genes evolve?.
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Figure 2.31 The exon structure of globin genes corresponds with protein function, but leghemoglob in has an extra intron in the central domain.2.10 How did interrupted genes evolve?.
Figure 2.32 The rat insulin gene with one intron evolved by losing an intron from an ancestor with two interruptions. 2.10 How did interrupted genes evolve?.
Figure 2.33 Actin genes vary widely in their organization. The sites of introns are indicated in purple; the number identifies the codon interrupted by the intron. 2.10 How did interrupted genes evolve?.
2.11 The scope of the paradigm
Summary
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