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Ch. 15 - Recombinant DNA Technology and Its Applications
Sanders - Genetic Analysis: An Integrated Approach 3rd Edition
Sanders3rd EditionGenetic Analysis: An Integrated ApproachISBN: 9780135564172Not the one you use?Change textbook
All textbooksSanders 3rd EditionCh. 15 - Recombinant DNA Technology and Its ApplicationsProblem E.12a
Chapter 15, Problem E.12a

Three independently assorting STR markers (A, B, and C) are used to assess the paternity of a colt recently born to a quarter horse mare. Blood samples are drawn from the mare, her colt, and three possible male sires (S₁, S₂, and S₃). DNA at each marker locus is amplified by PCR, and a DNA electrophoresis gel is run for each marker. Amplified DNA bands are visualized in each gel by ethidium bromide staining. Gel results are shown below for each marker. Evaluate the data and determine if any of the potential sires can be excluded. Explain the basis of exclusion, if any, in each case.

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Step 1: Understand the principle of paternity testing using STR markers. Each individual inherits one allele from the mother and one allele from the father at each STR locus. Therefore, the colt's alleles at each marker must be a combination of one allele from the mare and one allele from the sire.
Step 2: For each STR marker (A, B, and C), compare the alleles present in the colt with those of the mare. Identify which allele in the colt must have come from the sire by excluding the allele inherited from the mare.
Step 3: For each potential sire (S₁, S₂, and S₃), check if they possess the allele(s) that the colt must have inherited from the father at each marker. If a potential sire lacks the required allele at any marker, that sire can be excluded as the biological father.
Step 4: Repeat this comparison for all three markers independently, since the markers assort independently. A sire must have matching alleles at all markers to be considered a possible father.
Step 5: Summarize the results by listing which sires can be excluded based on the absence of required alleles at one or more markers, and explain that exclusion is based on Mendelian inheritance patterns where the colt must inherit one allele from each parent at every locus.

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Key Concepts

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

Independent Assortment of STR Markers

Short Tandem Repeat (STR) markers are specific DNA sequences used in genetic profiling. When markers assort independently, the inheritance of one marker does not affect the others, allowing each locus to be analyzed separately. This principle helps in paternity testing by comparing alleles at multiple loci to increase accuracy.
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Paternity Exclusion Principle

Paternity exclusion occurs when an alleged sire lacks one or more alleles present in the offspring that must have been inherited from the father. If the sire’s genotype does not share at least one allele at each marker locus with the offspring, he can be excluded as the biological father.
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PCR Amplification and Gel Electrophoresis in DNA Analysis

Polymerase Chain Reaction (PCR) amplifies specific DNA regions, such as STR loci, to detectable levels. Gel electrophoresis separates these amplified fragments by size, visualized by ethidium bromide staining. The resulting band patterns represent alleles, which are compared across individuals for genetic relationship analysis.
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Step 2
Related Practice
Textbook Question

Compare and contrast methods for making transgenic plants and transgenic Drosophila.

Textbook Question

In an inheritance case, a man has died leaving his estate to be divided equally between 'his wife and his offspring.' His wife (M) has an adult daughter (D), and they argue that they should split the estate equally. As a young couple, however, the man and his wife had a son that they gave up for adoption. Two men have appeared, each claiming to be the son of the couple and therefore entitled to a one-third share of the estate. The accompanying illustration shows the results of DNA analysis for five genes for the mother (M), her daughter (D), and the two claimants (S1 and S2). Do the DNA results suggest that either man is likely to be the son of the man and his wife? Explain.

Textbook Question

In an inheritance case, a man has died leaving his estate to be divided equally between 'his wife and his offspring.' His wife (M) has an adult daughter (D), and they argue that they should split the estate equally. As a young couple, however, the man and his wife had a son that they gave up for adoption. Two men have appeared, each claiming to be the son of the couple and therefore entitled to a one-third share of the estate. The accompanying illustration shows the results of DNA analysis for five genes for the mother (M), her daughter (D), and the two claimants (S1 and S2). How many nonmaternal DNA bands are shared by D and S1? By D and S2?

Textbook Question

Three independently assorting STR markers (A, B, and C) are used to assess the paternity of a colt recently born to a quarter horse mare. Blood samples are drawn from the mare, her colt, and three possible male sires (S₁, S₂, and S₃). DNA at each marker locus is amplified by PCR, and a DNA electrophoresis gel is run for each marker. Amplified DNA bands are visualized in each gel by ethidium bromide staining. Gel results are shown below for each marker. Calculate the PI and CPI based on these STR markers, using the following population frequencies: A₁₂ = 0.12, A₁₀ = 0.18; B₁₈ = 0.08, B₁₂ = 0.17; C₁₆ = 0.11, C₁₄ = 0.20.

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Textbook Question
It is often desirable to insert cDNAs into a cloning vector in such a way that all the cDNA clones will have the same orientation with respect to the sequences of the plasmid. This is referred to as directional cloning. Outline how you would directionally clone a cDNA library in the plasmid vector pUC18.
Textbook Question
A major advance in the 1980s was the development of technology to synthesize short oligonucleotides. This work both facilitated DNA sequencing and led to the advent of the development of PCR. Recently, rapid advances have occurred in the technology to chemically synthesize DNA, and sequences up to 10 kb are now readily produced. As this process becomes more economical, how will it affect the gene-cloning approaches outlined in this chapter? In other words, what types of techniques does this new technology have potential to supplant, and what techniques will not be affected by it?