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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.6a
Chapter 15, Problem E.6a

A victim of murder is found to have scrapings containing skin cells under several of her fingernails. Genetic analysis confirms that the DNA isolated from these cells came from the same individual and does not match the DNA of the victim. The results shown below are for six CODIS STR markers from the crime scene DNA (from under the victim's fingernails and presumed to be the murderer's), and from three suspects (A, B, and C) who have been detained for questioning about the murder. Do the STR results exclude any of the three suspects? Explain.

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Step 1: Understand the context and the role of CODIS STR markers. CODIS (Combined DNA Index System) uses specific Short Tandem Repeat (STR) loci to compare DNA samples. Each STR marker consists of repeating units of DNA, and individuals differ in the number of repeats at each locus, making STR profiles highly individual-specific.
Step 2: Compare the STR profiles from the crime scene DNA (under the victim's fingernails) with the STR profiles of each suspect (A, B, and C). For each of the six STR markers, check if the alleles (repeat numbers) in the crime scene sample match those of each suspect.
Step 3: For each suspect, identify any STR markers where the alleles do not match the crime scene DNA. A mismatch at even one STR locus can exclude a suspect because it indicates that the suspect's DNA profile is not consistent with the DNA found at the crime scene.
Step 4: Summarize the comparison results by listing which suspects have matching STR profiles at all six loci and which have mismatches. Those with complete matches cannot be excluded, while those with mismatches can be excluded as the source of the DNA under the victim's fingernails.
Step 5: Conclude by explaining that the exclusion or inclusion of suspects is based on the presence or absence of matching STR alleles across all tested loci, emphasizing the power of STR analysis in forensic identification.

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Key Concepts

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

Short Tandem Repeats (STRs)

STRs are short sequences of DNA, typically 2-6 base pairs long, repeated multiple times in a row at specific loci. The number of repeats varies among individuals, making STRs highly useful for genetic fingerprinting and forensic identification. Comparing STR patterns helps determine if DNA samples come from the same person.
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DNA Profiling and Matching

DNA profiling involves analyzing multiple STR markers to create a genetic profile unique to an individual. Matching STR profiles between crime scene samples and suspects can include or exclude individuals as contributors. A suspect is excluded if their STR alleles do not match the crime scene DNA at one or more loci.
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Forensic Interpretation of STR Results

Forensic analysis compares STR profiles from evidence and suspects to assess identity. If all STR markers match, the suspect cannot be excluded; if any marker differs, the suspect is excluded. Understanding allele matching and the significance of multiple loci is essential for interpreting forensic DNA evidence accurately.
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Related Practice
Textbook Question

Using the genomic libraries, you wish to clone the human gene encoding myostatin, which is expressed only in muscle cells.

How frequently will a clone representing myostatin be found in the cDNA library made from brain?

Textbook Question

The human genome is 3×10⁹ bp. You wish to design a primer to amplify a specific gene in the genome. In general, what length of oligonucleotide would be sufficient to amplify a single unique sequence? To simplify your calculation, assume that all bases occur with an equal frequency.

Textbook Question

A victim of murder is found to have scrapings containing skin cells under several of her fingernails. Genetic analysis confirms that the DNA isolated from these cells came from the same individual and does not match the DNA of the victim. The results shown below are for six CODIS STR markers from the crime scene DNA (from under the victim's fingernails and presumed to be the murderer's), and from three suspects (A, B, and C) who have been detained for questioning about the murder. Is there a failure to exclude any of the suspects? Explain.

Textbook Question

The results shown are from a DNA test for four genes used in a paternity identification case. DNA for the mother (M) and her child (C) are shown along with DNA from two possible fathers, F1 and F2. Based on the exclusion principle, is either man excluded as the possible father? Explain.

Textbook Question

The results shown are from a DNA test for four genes used in a paternity identification case. DNA for the mother (M) and her child (C) are shown along with DNA from two possible fathers, F1 and F2. What can you conclude based on the DNA results available?

Textbook Question

The results shown are from a DNA test for four genes used in a paternity identification case. DNA for the mother (M) and her child (C) are shown along with DNA from two possible fathers, F1 and F2. In the 'C' column, label the DNA bands contributed by the mother with 'M' and the DNA bands contributed by the father with 'F.'

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