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Chapter 24 introduction to genomics: DNA sequencing on a genomic scale. We will begin this chapter with a discussion of positional cloning, a technique for identifying a gene responsible for a given trait, and see how much easier this process is when the sequence of the organism’s genome is known. Then we will examine the techniques scientists use to sequence DNA on a massive scale. We will also discuss some of the lessons we have learned from the sequences of genomes, especially the evolutionary insights to be gained by comparing the genomic sequences of different organisms. | Molecular Biology Fifth Edition Chapter 24 Introduction to Genomics: DNA Sequencing on a Genomic Scale Lecture PowerPoint to accompany Robert F. Weaver Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 24.1 Positional Cloning Positional cloning is a method for the discovery of genes involved in genetic traits Positional cloning was very difficult in the absence of genomic information Begins with mapping studies to pin down the location of the gene of interest to a relatively small region of DNA 24- Classical Tools of Positional Cloning Mapping depends on a set of landmarks to which gene position can be related Restriction Fragment Length Polymorphisms (RFLP) are landmarks with lengths of restriction fragments given by a specific enzyme that vary from one individual to another Exon Traps use a special vector to help clone exons only CpG Islands are DNA regions containing unmethylated CpG sequences 24- Detecting RFLPs 24- Exon . | Molecular Biology Fifth Edition Chapter 24 Introduction to Genomics: DNA Sequencing on a Genomic Scale Lecture PowerPoint to accompany Robert F. Weaver Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 24.1 Positional Cloning Positional cloning is a method for the discovery of genes involved in genetic traits Positional cloning was very difficult in the absence of genomic information Begins with mapping studies to pin down the location of the gene of interest to a relatively small region of DNA 24- Classical Tools of Positional Cloning Mapping depends on a set of landmarks to which gene position can be related Restriction Fragment Length Polymorphisms (RFLP) are landmarks with lengths of restriction fragments given by a specific enzyme that vary from one individual to another Exon Traps use a special vector to help clone exons only CpG Islands are DNA regions containing unmethylated CpG sequences 24- Detecting RFLPs 24- Exon Trapping 24- Identifying the Gene Mutated in a Human Disease Using RFLPs, geneticists mapped the Huntington disease gene (HD) to a region near the end of chromosome 4 Used an exon trap to identify the gene itself Mutation causing the disease is an expansion of a CAG repeat from the normal range of 11-34 copies to abnormal range of at least 38 copies Extra repeats cause extra Glu inserted into huntingtin, the product of the HD gene 24- Phage X174 Genome First genome sequenced was a very simple one, phage X174 Completed by Sanger in 1977 5375-nucleotides Note that some of these phage genes overlap 24- 24.2 Techniques in Genomic Sequencing What information can be gleaned from genome sequence? Location of exact coding regions for all the genes Spatial relationships among all the genes and exact distances between them How is a coding region recognized? Contains an ORF long enough to code for a phage protein ORF must Start with ATG triplet End with stop codon Phage or bacterial ORF
