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Ch. 20 - Recombinant DNA Technology
Chapter 19, Problem 25

Microsatellites are currently exploited as markers for paternity testing. A sample paternity test is shown in the following table in which ten microsatellite markers were used to test samples from a mother, her child, and an alleged father. The name of the microsatellite locus is given in the left-hand column, and the genotype of each individual is recorded as the number of repeats he or she carries at that locus. For example, at locus D9S302, the mother carries 30 repeats on one of her chromosomes and 31 on the other. In cases where an individual carries the same number of repeats on both chromosomes, only a single number is recorded. (Some of the numbers are followed by a decimal point, for example, 20.2, to indicate a partial repeat in addition to the complete repeats.) Assuming that these markers are inherited in a simple Mendelian fashion, can the alleged father be excluded as the source of the sperm that produced the child? Why or why not? Explain.

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Identify the alleles (number of repeats) present at each microsatellite locus for the mother, child, and alleged father.
Determine the alleles that the child must have inherited from the mother at each locus, based on the mother's genotype.
For each locus, identify the allele(s) that the child could have inherited from the alleged father, given the child's genotype and the allele(s) inherited from the mother.
Check if the alleged father has the necessary allele(s) at each locus to account for the child's genotype, considering the allele(s) inherited from the mother.
If there is any locus where the alleged father does not have the necessary allele(s) to account for the child's genotype, he can be excluded as the biological father. Otherwise, he cannot be excluded based on these markers.

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Key Concepts

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

Microsatellites

Microsatellites, or short tandem repeats (STRs), are repetitive sequences of DNA that vary in length among individuals. They are highly polymorphic, meaning they have many different alleles in a population, making them useful for genetic profiling. In paternity testing, the number of repeats at specific loci is compared between the mother, child, and alleged father to determine genetic relationships.
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Mendelian Inheritance

Mendelian inheritance refers to the principles of genetic inheritance established by Gregor Mendel, which include the segregation and independent assortment of alleles. In the context of microsatellites, this means that a child inherits one allele from each parent at each locus. Understanding this concept is crucial for determining whether the alleged father can be excluded based on the genotypes observed in the paternity test.
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Paternity Testing

Paternity testing involves comparing genetic markers between a child and potential fathers to establish biological relationships. In this case, the presence or absence of specific microsatellite alleles in the alleged father that match those of the child is analyzed. If the alleged father does not possess an allele that the child has inherited from the mother, he can be excluded as the biological father.
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Related Practice
Textbook Question

Following the tragic shooting of 20 children at a school in Newtown, Connecticut, in 2012, Connecticut's state medical examiner requested a full genetic analysis of the killer's genome. What do you think investigators might be looking for? What might they expect to find? Might this analysis lead to oversimplified analysis of the cause of the tragedy?

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Textbook Question

How is fluorescent in situ hybridization (FISH) used to produce a spectral karyotype?

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Textbook Question

Private companies are offering personal DNA sequencing along with interpretation. What services do they offer? Do you think that these services should be regulated, and if so, in what way? Investigate one such company, 23andMe, at http://www.23andMe.com, before answering these questions.

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Textbook Question

As you will learn later in the text (Special Topics Chapter 1— CRISPR-Cas and Genome Editing), the CRISPR-Cas system has great potential but also raises many ethical issues about its potential applications because theoretically it can be used to edit any gene in the genome. What do you think are some of the concerns about the use of CRISPR-Cas on humans? Should CRISPR-Cas applications be limited for use on only certain human genes but not others? Explain your answers.

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Textbook Question

The gel presented here shows the pattern of bands of fragments produced with several restriction enzymes. The enzymes used are identified above the lanes of the gel, and six possible restriction maps are shown in the column to the right.

One of the six restriction maps shown is consistent with the pattern of bands shown in the gel.

From your analysis of the pattern of bands on the gel, select the correct restriction map and explain your reasoning. <>.

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Textbook Question

The gel presented here shows the pattern of bands of fragments produced with several restriction enzymes. The enzymes used are identified above the lanes of the gel, and six possible restriction maps are shown in the column to the right.

One of the six restriction maps shown is consistent with the pattern of bands shown in the gel.

The highlighted bands (magenta) in the gel hybridized with a probe for the gene pep during a Southern blot. Where in the gel is the pep gene located? 

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