FDC Statistical Analysis & Population Genetics 1 — Questions and Answers
Question 1: Which principle states that allele and genotype frequencies remain constant from generation to generation in a large, randomly mating population with no selection, mutation, or migration?
- Hardy-Weinberg Equilibrium (Correct answer)
- Product Rule
- Ceiling Principle
- Bayesian Theorem
Correct answer: Hardy-Weinberg Equilibrium
Hardy-Weinberg Equilibrium describes the theoretical state in which allele and genotype frequencies remain stable across generations under ideal conditions, forming the statistical foundation for forensic DNA frequency calculations.
Question 2: In forensic DNA analysis, the Random Match Probability (RMP) represents:
- The probability that two unrelated individuals share the same DNA profile by chance (Correct answer)
- The probability that a suspect is guilty given a DNA match
- The probability that the DNA evidence was contaminated
- The probability that laboratory error caused a false match
Correct answer: The probability that two unrelated individuals share the same DNA profile by chance
RMP is the probability that a randomly selected, unrelated individual from the population would coincidentally share the same DNA profile as the evidence, expressing the rarity of the profile.
Question 3: To calculate the expected heterozygote frequency at a single STR locus under Hardy-Weinberg Equilibrium for alleles with frequencies p and q, the formula is:
- 2pq (Correct answer)
- p² + q²
- p + q
- p² × q²
Correct answer: 2pq
Under Hardy-Weinberg Equilibrium, the expected frequency of a heterozygous genotype (two different alleles) is 2pq, where p and q are the individual allele frequencies.
Question 4: The Product Rule in forensic DNA statistics is applied to:
- Multiply individual locus genotype frequencies across multiple STR loci to obtain a combined profile frequency (Correct answer)
- Add allele frequencies to determine overall rarity
- Determine the likelihood ratio from a mixture
- Calculate the theta correction factor for substructure
Correct answer: Multiply individual locus genotype frequencies across multiple STR loci to obtain a combined profile frequency
The Product Rule allows analysts to combine genotype frequencies across independent STR loci by multiplication, yielding the overall profile frequency assuming independence between loci.
Question 5: The theta (θ) correction factor is applied in forensic DNA statistics to account for:
- Population substructure that may cause allele frequencies to differ among ethnic subgroups (Correct answer)
- Laboratory measurement error in electrophoresis
- Degradation of DNA affecting allele dropout
- Stutter artifacts in PCR amplification
Correct answer: Population substructure that may cause allele frequencies to differ among ethnic subgroups
Theta correction adjusts genotype frequency estimates to account for population substructure, where individuals within an ethnic subgroup may be more closely related than expected under simple random mating.
Question 6: According to NRC II recommendations, which value of theta is commonly used as a conservative correction for population substructure in forensic casework?
- 0.01 (Correct answer)
- 0.10
- 0.50
- 0.001
Correct answer: 0.01
NRC II recommended using theta = 0.01 as a conservative default correction for population substructure, acknowledging that modest levels of genetic differentiation exist within major population groups.
Question 7: Which NIST resource provides population allele frequency data for STR loci commonly used in forensic DNA typing in the United States?
- STRbase / NIST STR Data Entry (Correct answer)
- CODIS NDIS database
- FBI Combined DNA Index
- SwissProt protein database
Correct answer: STRbase / NIST STR Data Entry
NIST's STRbase (and its successor STR Data Entry) provides curated allele frequency tables for STR loci across major U.S. population groups, which forensic analysts use for statistical calculations.
FDC Statistical Analysis & Population Genetics 1
Which principle states that allele and genotype frequencies remain constant from generation to generation in a large, randomly mating population with no selection, mutation, or migration?