Does genetic analysis by ASO testing allow for detection of epigenetic changes that may contribute to a genetic disorder? Explain your answer.
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
- 19. Cancer Genetics29m
- 20. Quantitative Genetics1h 26m
- 21. Population Genetics50m
- 22. Evolutionary Genetics29m
18. Molecular Genetic Tools
Methods for Analyzing DNA
Problem E.12b
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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Step 1: Identify the genotypes of the mare, colt, and each potential sire (S₁, S₂, and S₃) at each STR marker (A, B, and C) from the gel electrophoresis results. This involves determining which alleles are present for each individual at each locus.
Step 2: For each marker, determine the possible paternal allele(s) that the colt could have inherited from the sire by comparing the colt's genotype to the mare's genotype. The allele(s) in the colt not present in the mare must have come from the sire.
Step 3: Calculate the Paternity Index (PI) for each marker. The PI is the likelihood ratio comparing the probability that the alleged sire transmitted the paternal allele to the colt versus the probability that a random, unrelated male from the population transmitted that allele. Use the formula: if the alleged sire is homozygous for the paternal allele, or if heterozygous, where is the population frequency of the paternal allele.
Step 4: Multiply the individual PIs from each marker to obtain the Combined Paternity Index (CPI). This is done by calculating , where each corresponds to the PI at marker X.
Step 5: Interpret the CPI value to assess paternity. A higher CPI indicates stronger genetic evidence that the tested sire is the biological father of the colt. Typically, a CPI greater than 1000 is considered strong evidence of paternity.

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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Short Tandem Repeat (STR) Markers
STR markers are DNA regions where short sequences are repeated consecutively. They are highly polymorphic, making them useful for genetic identification and paternity testing. Each individual inherits one allele from each parent, allowing comparison of STR profiles between offspring and potential parents.
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Paternity Index (PI) and Combined Paternity Index (CPI)
The Paternity Index (PI) quantifies the likelihood that a tested male is the biological father at a single genetic locus, based on allele frequencies. The Combined Paternity Index (CPI) multiplies PIs across multiple loci, providing a cumulative probability to support or exclude paternity with higher confidence.
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Allele Frequency and Probability Calculations in Forensic Genetics
Allele frequencies represent how common specific alleles are in a population and are essential for calculating the probability of genetic matches. These frequencies are used in formulas to compute PI by comparing observed alleles in offspring and alleged fathers, accounting for population genetics principles.
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