Textbook Question
When the whole-genome shotgun sequence of the Drosophila genome was assembled, it comprised 134 scaffolds made up of 1636 contigs.
How can sequence gaps be closed?
Ch. 16 - Genomics: Genetics from a Whole-Genome Perspective
Sanders3rd EditionGenetic Analysis: An Integrated ApproachISBN: 9780135564172
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Table of contents
- Ch. 1 - The Molecular Basis of Heredity, Variation, and Evolution64
- Ch. 2 - Transmission Genetics144
- Ch. 3 - Cell Division and Chromosome Heredity81
- Ch. 4 - Gene Interaction87
- Ch. 5 - Genetic Linkage and Mapping in Eukaryotes103
- Ch. 6 - Genetic Analysis and Mapping in Bacteria and Bacteriophages73
- Ch. 7 - DNA Structure and Replication71
- Ch. 8 - Molecular Biology of Transcription and RNA Processing79
- Ch. 9 - The Molecular Biology of Translation110
- Ch. 10 - Eukaryotic Chromosome Abnormalities and Molecular Organization100
- Ch. 11 - Gene Mutation, DNA Repair, and Homologous Recombination86
- Ch. 12 - Regulation of Gene Expression in Bacteria and Bacteriophage90
- Ch. 13 - Regulation of Gene Expression in Eukaryotes38
- Ch. 14 - Analysis of Gene Function via Forward Genetics and Reverse Genetics72
- Ch. 15 - Recombinant DNA Technology and Its Applications69
- Ch. 16 - Genomics: Genetics from a Whole-Genome Perspective49
- Ch. 17 - Organelle Inheritance and the Evolution of Organelle Genomes27
- Ch. 18 - Developmental Genetics43
- Ch. 19 - Genetic Analysis of Quantitative Traits66
- Ch. 20 - Population Genetics and Evolution at the Population, Species, and Molecular Levels105
Sanders3rd EditionGenetic Analysis: An Integrated ApproachISBN: 9780135564172Not the one you use?Change textbook
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Sanders 3rd EditionCh. 16 - Genomics: Genetics from a Whole-Genome PerspectiveProblem 3c
Sanders 3rd EditionCh. 16 - Genomics: Genetics from a Whole-Genome PerspectiveProblem 3cChapter 16, Problem 3c
When the whole-genome shotgun sequence of the Drosophila genome was assembled, it comprised 134 scaffolds made up of 1636 contigs. How can physical gaps be closed?
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Understand the concept of physical gaps: Physical gaps in genome assembly occur when there is missing sequence information between contigs that cannot be bridged by computational methods alone. These gaps need to be closed using experimental techniques.
Step 1: Use paired-end sequencing data. Paired-end reads provide information about the relative positions of sequences on the genome. If the paired reads span a gap, they can help identify the missing sequence and close the gap.
Step 2: Apply PCR amplification. Design primers flanking the gap regions based on the known sequences of adjacent contigs. Amplify the DNA in the gap using PCR and sequence the amplified product to fill the missing information.
Step 3: Utilize long-read sequencing technologies. Technologies like PacBio or Oxford Nanopore can generate longer reads that span gaps, providing direct sequence information for the missing regions.
Step 4: Perform chromosome walking or library screening. Use a genomic library to identify clones that contain sequences bridging the gap. Sequence these clones to close the physical gaps.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Whole-Genome Shotgun Sequencing
Whole-genome shotgun sequencing is a method used to sequence an entire genome by randomly breaking the DNA into small fragments, which are then sequenced and assembled into a complete sequence. This approach allows for the rapid generation of genomic data, but it often results in gaps due to the random nature of fragment selection, necessitating further techniques to close these gaps.
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Sequencing Overview
Scaffolds and Contigs
In genome assembly, contigs are contiguous sequences of DNA that are formed by overlapping fragments, while scaffolds are larger structures that consist of multiple contigs linked together. Scaffolds provide a more complete representation of the genome, but gaps may still exist between contigs, which can be addressed through additional sequencing or mapping techniques to improve assembly accuracy.
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Gap Closure Techniques
Gap closure techniques involve various methods to fill in the physical gaps between contigs in a genome assembly. These methods can include targeted sequencing of the gap regions, using paired-end reads to bridge gaps, or employing long-read sequencing technologies that can span larger distances, thereby enhancing the completeness and accuracy of the genomic assembly.
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Related Practice
Textbook Question
When the whole-genome shotgun sequence of the Drosophila genome was assembled, it comprised 134 scaffolds made up of 1636 contigs. Why were there so many more contigs than scaffolds?
Textbook Question
Repetitive DNA poses problems for genome sequencing. What strategies can be employed to overcome these problems?
Textbook Question
How do comparisons between genomes of related species help refine gene annotation?
Textbook Question
How do cDNA sequences facilitate gene annotation? Describe how the use of full-length cDNAs facilitates discovery of alternative splicing.
Textbook Question
When the whole-genome shotgun sequence of the Drosophila genome was assembled, it comprised 134 scaffolds made up of 1636 contigs. What is the difference between physical and sequence gaps?