Textbook Question
What is the exclusion principle? How is it used in forensic genetic analysis and in paternity determination?
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18. Molecular Genetic Tools
Methods for Analyzing DNA
3:18 minutesProblem 5a
Textbook Question
Using the genomic libraries, you wish to clone the human gene encoding myostatin, which is expressed only in muscle cells.
Assuming the human genome is 3x10⁹ bp and that the average insert size in the genomic libraries is 100 kb, how frequently will a clone representing myostatin be found in the genomic library made from muscle?
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Determine the total number of clones in the genomic library by dividing the size of the human genome by the average insert size. Use the formula: .
Simplify the calculation to find the total number of clones in the library. This will give you the total number of fragments the genome is divided into, based on the insert size.
Understand that myostatin is expressed only in muscle cells, but the genomic library is constructed from the entire genome. Therefore, the probability of finding a clone representing myostatin is proportional to the size of the myostatin gene relative to the total genome size.
Estimate the size of the myostatin gene (if not provided, assume a typical gene size, e.g., 10 kb). Then calculate the probability of a single clone containing the myostatin gene using the formula: .
Multiply the probability of a single clone containing the myostatin gene by the total number of clones in the library to estimate how frequently a clone representing myostatin will be found.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Genomic Libraries
Genomic libraries are collections of DNA fragments that represent the entire genome of an organism. These libraries are created by cloning DNA into vectors, allowing researchers to isolate and study specific genes. Each clone in the library contains a fragment of the genome, and the size of these fragments can vary, impacting the likelihood of finding a specific gene, such as myostatin.
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Genomics Overview
Gene Cloning
Gene cloning is the process of making multiple copies of a specific gene or DNA sequence. This involves inserting the gene of interest into a vector, which is then introduced into a host cell, allowing for replication. In this context, cloning the myostatin gene requires understanding its sequence and ensuring it is expressed in muscle cells, where it is naturally found.
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Insert Size and Frequency of Clones
The insert size in a genomic library refers to the average length of DNA fragments cloned into vectors. In this case, with an average insert size of 100 kb and a human genome size of approximately 3 billion base pairs, the frequency of finding a specific gene like myostatin can be estimated. The larger the insert size, the fewer clones are needed to cover the entire genome, affecting the probability of encountering the desired gene.
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