Ch. 15 - Recombinant DNA Technology and Its Applications

Sanders - Genetic Analysis: An Integrated Approach 3rd Edition

Sanders3rd EditionGenetic Analysis: An Integrated ApproachISBN: 9780135564172당신이 사용하는 게 아니라요?교과서 변경

Sanders 3rd Edition

Ch. 15 - Recombinant DNA Technology and Its Applications

문제 E.12b

15장, 문제 E.12b

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.

검증된 단계별 안내

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:

PI = \frac{1}{p}

if the alleged sire is homozygous for the paternal allele, or

PI = \frac{1}{2p}

if heterozygous, where

p

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

CPI = {PI}_{A} \cdot {PI}_{B} \cdot {PI}_{C}

, where each

{PI}_{X}

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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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.

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.

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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교과서 질문

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교과서 질문

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?

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