Table of contents

1. Introduction to Genetics51m
2. Mendel's Laws of Inheritance3h 37m
3. Extensions to Mendelian Inheritance2h 41m
4. Genetic Mapping and Linkage2h 28m
5. Genetics of Bacteria and Viruses1h 21m
6. Chromosomal Variation1h 48m
7. DNA and Chromosome Structure56m
8. DNA Replication1h 10m
9. Mitosis and Meiosis1h 34m
10. Transcription1h 0m
11. Translation58m
12. Gene Regulation in Prokaryotes1h 19m
13. Gene Regulation in Eukaryotes44m
14. Genetic Control of Development44m
15. Genomes and Genomics1h 50m
16. Transposable Elements47m
17. Mutation, Repair, and Recombination1h 6m
18. Molecular Genetic Tools19m
- Genetic Cloning
  9m
- Methods for Analyzing DNA
  9m
19. Cancer Genetics29m
- Overview of Cancer
  21m
- Cancer Mutations
  7m
20. Quantitative Genetics1h 26m
21. Population Genetics50m
- Hardy Weinberg
  19m
- Allelic Frequency Changes
  31m
22. Evolutionary Genetics29m

18. Molecular Genetic Tools

Methods for Analyzing DNA

Genetics

18. Molecular Genetic Tools

Methods for Analyzing DNA

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3:13 minutes

Problem 15b

Textbook Question

The bacteriophage lambda genome can exist in either a linear form or a circular form.
Diagram the resulting fragments as they would appear on an agarose gel after electrophoresis.

Verified step by step guidance

Understand the context: The bacteriophage lambda genome can exist in two forms—linear and circular. Linear DNA will produce distinct fragments when digested with restriction enzymes, while circular DNA may produce different patterns due to the absence of free ends.

Identify the restriction enzyme used: Determine which restriction enzyme is applied to the DNA. Each enzyme cuts at specific recognition sites, producing fragments of predictable sizes. For example, EcoRI recognizes the sequence GAATTC and cuts between G and A.

Predict the fragment sizes: For the linear form, calculate the sizes of fragments based on the known positions of restriction sites along the genome. Use the genome map to determine the distances between consecutive restriction sites.

Consider the circular form: In circular DNA, the restriction enzyme cuts at the same recognition sites, but the absence of free ends means the fragments may differ. For example, one fragment may represent the remainder of the circular genome after the first cut.

Diagram the gel: Represent the fragments as bands on an agarose gel. Larger fragments will migrate slower and appear closer to the top, while smaller fragments will migrate faster and appear closer to the bottom. Label the bands with their corresponding fragment sizes for both linear and circular forms.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Bacteriophage Lambda Genome Structure

The bacteriophage lambda genome can exist in two forms: linear and circular. The linear form is typically found during the lytic cycle, where the virus injects its DNA into a host cell, while the circular form is associated with the lysogenic cycle, where the viral DNA integrates into the host genome. Understanding these forms is crucial for predicting how the DNA will behave during gel electrophoresis.

Gel Electrophoresis

Gel electrophoresis is a technique used to separate DNA fragments based on their size. When an electric current is applied, negatively charged DNA moves towards the positive electrode, with smaller fragments migrating faster than larger ones. This method allows visualization of the DNA fragments, which is essential for analyzing the results of the bacteriophage lambda genome's different forms.

Fragmentation Patterns

The fragmentation patterns of DNA during gel electrophoresis depend on the form of the genome and the restriction enzymes used. Linear DNA typically produces distinct bands corresponding to the sizes of the fragments generated, while circular DNA may appear as a single band or multiple bands depending on its conformation and any cuts made. Recognizing these patterns is key to accurately diagramming the results on an agarose gel.

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Textbook Question

What is the main purpose of genome-wide association studies (GWAS)? How can information from GWAS be used to inform scientists and physicians about genetic diseases?

Describe how the team from the J. Craig Venter Institute created a synthetic genome. How did the team demonstrate that the genome converted the recipient strain of bacteria into a different strain?

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Textbook Question

In a control experiment, a plasmid containing a HindIII recognition sequence within a kanamycin resistance gene is cut with HindIII, re-ligated, and used to transform E. coli K12 cells. Kanamycin-resistant colonies are selected, and plasmid DNA from these colonies is subjected to electrophoresis. Most of the colonies contain plasmids that produce single bands that migrate at the same rate as the original intact plasmid. A few colonies, however, produce two bands, one of original size and one that migrates much less far down the gel. Diagram the origin of this slow band as a product of ligation.

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Textbook Question

What advantages do cDNA libraries provide over genomic DNA libraries? Describe cloning applications where the use of a genomic library is necessary to provide information that a cDNA library cannot.

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Textbook Question

To create a cDNA library, cDNA can be inserted into vectors and cloned. In the analysis of cDNA clones, it is often difficult to find clones that are full length—that is, many clones are shorter than the mature mRNA molecules from which they are derived. Why is this so?

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Textbook Question

A hereditary disease is inherited as an autosomal recessive trait1. The wild-type allele of the disease gene produces a mature mRNA that is 1250 nucleotides (nt) long. Molecular analysis shows that the mature mRNA consists of four exons that measure 400 nt (exon 1), 320 nt (exon 2), 230 nt (exon 3), and 300 nt (exon 4). A mother and father with two healthy children and two children with the disease have northern blot analysis performed in a medical genetics laboratory. The results of the northern blot for each family member are shown here. Based on your analysis, what is the most likely molecular abnormality causing the disease allele?

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Textbook Question

A hereditary disease is inherited as an autosomal recessive trait1. The wild-type allele of the disease gene produces a mature mRNA that is 1250 nucleotides (nt) long. Molecular analysis shows that the mature mRNA consists of four exons that measure 400 nt (exon 1), 320 nt (exon 2), 230 nt (exon 3), and 300 nt (exon 4). A mother and father with two healthy children and two children with the disease have northern blot analysis performed in a medical genetics laboratory. The results of the northern blot for each family member are shown here. Identify the genotype of each family member, using the sizes of mRNAs to indicate each allele. (For example, a person who is homozygous wild type is indicated as '1250/1250.')

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Textbook Question

A 2-kb fragment of E. coli DNA contains the complete sequence of a gene for which transcription is terminated by the rho protein. The fragment contains the complete promoter sequence as well as the terminator region of the gene. The cloned fragment is examined by band shift assay. Each lane of a single electrophoresis gel contains the 2-kb cloned fragment under the following conditions:

Lane 1: 2-kb fragment alone

Lane 2: 2-kb fragment plus the core enzyme

Lane 3: 2-kb fragment plus the RNA polymerase holoenzyme

Lane 4: 2-kb fragment plus rho protein

Diagram the relative positions expected for the DNA fragments in this gel electrophoresis analysis.

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