Forensic Genetics Overview

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Questions and Answers

What information is indicated by a microvariant allele such as the 9.3 allele of the TH01 locus?

The total number of repeat units.

The location of the allele on the chromosome.

The number of complete repeats and the number of bases in the partial repeat. (correct)

The sequence of bases in the allele.

Which chromosome contains the D5S818 locus?

Chromosome 5 (correct)

Chromosome 7

Chromosome 12

Chromosome 3

What does the genotype or profile of a specimen consist of?

The collection of alleles tested across different loci. (correct)

The specific base pair sequence of one locus.

The average allele length of the tested loci.

The number of loci present in the specimen.

What is the purpose of Standard Reference Material supplied by the National Institute of Standards and Technology?

To assess the occurrence of a genotype in a population. Signup and view all the answers

How is genetic concordance defined in forensic analysis?

All alleles from two sources being the same across all loci. Signup and view all the answers

Which of these loci is located on chromosome 11?

TH01 Signup and view all the answers

What characterizes microvariants in genetic loci?

They include partial repeat units indicated by decimals. Signup and view all the answers

What does a matching genotype indicate in forensic contexts?

The possibility that individuals share a genetic characteristic. Signup and view all the answers

What is the estimated frequency of nucleotide differences in human genome sequences?

Every 1,000 to 1,500 bases Signup and view all the answers

Which of the following polymorphisms is NOT mentioned as a type routinely used in the laboratory?

TNRs Signup and view all the answers

What characteristic of the human leukocyte antigen (HLA) locus is highlighted in the content?

It is known for its variability and polymorphism. Signup and view all the answers

What was the primary purpose of using blood type in the 1920s?

For parentage testing Signup and view all the answers

What advancement in testing occurred forty years after the initial blood type testing?

Implementation of polymorphic HLAs Signup and view all the answers

Which of the following is associated with interspersed nucleotide elements (LINEs)?

They are highly repeated sequences. Signup and view all the answers

How effective were the early serological tests compared to the ABO system?

Marginally better Signup and view all the answers

What major role do the variable nucleotide sequences in the HLA locus play?

Establishing self-identity of the immune system Signup and view all the answers

Which restriction enzyme is commonly used in North American laboratories for RFLP protocols?

HaeIII Signup and view all the answers

What is the primary purpose of the Standard Reference Material (SRM) in RFLP analysis?

To maintain the reproducibility of RFLP processes Signup and view all the answers

In diploid organisms, how is chromosomal content inherited?

Half from each parent Signup and view all the answers

For what purpose can polymorphisms be used in genetic mapping?

As landmarks to locate other genes Signup and view all the answers

Which organization provides the materials for the Standard Reference Material for RFLP analysis?

National Institute of Standards and Technology (NIST) Signup and view all the answers

What is a manifestation of Mendelian inheritance in polygenic traits?

Combining effects of multiple alleles Signup and view all the answers

How can a paternity test infer a parent’s contribution of alleles?

From the combination of alleles in the child and the other parent Signup and view all the answers

What is a key factor in confirming that a disease has a genetic component?

Showing a close genetic association to a known marker Signup and view all the answers

What happens to the certainty of a unique profile as the number of loci tested increases?

It increases, creating a unique identification. Signup and view all the answers

What does the Hardy-Weinberg equilibrium assume?

Large population with random mating. Signup and view all the answers

Which equation represents the population frequency of two alleles under the Hardy-Weinberg law?

$p^2 + 2pq + q^2 = 1.0$ Signup and view all the answers

How are allele frequencies characterized among different subpopulations?

They vary significantly based on ethnic groups. Signup and view all the answers

What conditions must be met for the Hardy-Weinberg law to apply?

Population size must be large and mating must be random. Signup and view all the answers

What does a likelihood ratio represent in the context of genotype matching?

The comparison of an unknown genotype to a known reference sample. Signup and view all the answers

What is the implication of decreased frequency of alleles in a population?

It increases the likelihood of a unique identification. Signup and view all the answers

What does the Hardy-Weinberg law fail to account for?

Immigration and emigration influences. Signup and view all the answers

What does a likelihood ratio greater than 1 indicate?

It is more likely that the genotypes came from the same person. Signup and view all the answers

What does the product rule rely on in a population?

The independence of allele frequencies. Signup and view all the answers

How is the overall frequency (OF) of a genotype calculated?

By multiplying the frequency of each allele represented in the genotype. Signup and view all the answers

What does a likelihood ratio of 1 indicate?

The genotypes are equally likely from the same or different individuals. Signup and view all the answers

What is assumed under linkage equilibrium?

Observed haplotype frequencies align with genetically predicted frequencies. Signup and view all the answers

What does an allele frequency of 1/1,000 imply in a population?

For 100,000 individuals, approximately 100 might share the same genotype. Signup and view all the answers

In terms of likelihood ratios, what does a ratio of less than 1 signify?

The genotypes are more likely from different individuals. Signup and view all the answers

What do allele frequencies often reflect within a population?

Distribution and diversity of genetic traits. Signup and view all the answers

How does changing prior odds assumptions affect the final probability of paternity?

It changes the final probability based on the specific CPI. Signup and view all the answers

What is a more complicated statistical analysis than a paternity test?

Sibling test Signup and view all the answers

What is the likelihood ratio generated by a sibling test sometimes referred to as?

Kinship index Signup and view all the answers

What is the assumption made by the laboratory regarding the prior odds in a paternity test?

A 50/50 chance of being the father. Signup and view all the answers

In a half-sibling test, what is being determined?

If two individuals share one common parent. Signup and view all the answers

Why do mutations and allele frequencies complicate sibling test analyses?

They can alter the expected outcomes. Signup and view all the answers

What would typically lead to a more confident conclusion in sibling tests?

Conducting tests with multiple siblings. Signup and view all the answers

What is the probability of paternity formula based on according to the assumptions made?

CPI multiplied by prior odds. Signup and view all the answers

Study Notes

DNA Polymorphisms and Human Identification

DNA polymorphisms are variations in DNA sequences shared by a percentage of a population.
They range from a single base pair to thousands of base pairs.
Polymorphisms are frequent in some regions of the genome, like the HLA locus, important for immune self-identity.

Types of Polymorphisms

RFLP Typing (Restriction Fragment Length Polymorphism):
- Identifies differences in DNA fragment sizes after restriction enzyme digestion.
- Used for genetic mapping, parentage testing, and human identification.
- Requires specific restriction enzymes, DNA size analysis (Southern blot).
VNTR Typing (Variable Number Tandem Repeats):
- Based on repeated sequences.
- Detected using Southern blot.
STR Typing (Short Tandem Repeats/Microsatellites):
- Short repeated sequences of 1-10 base pairs.
- Amplified by PCR.
- Used for human identification, parentage testing.
- Advantages: efficient amplification, minimal DNA needed.
SNP Typing (Single Nucleotide Polymorphism):
- Single nucleotide differences.
- Detected by sequencing.
- Used for genetic mapping of disease genes, population studies.
Mitochondrial DNA Typing:
- Used for human identification, especially in cases where nuclear DNA is degraded.
- Inheritance is maternal.
Protein-based Identification:
- Protein polymorphisms, amino acid sequence variations.
- Can be used as an alternative or supplementary forensic method.

Objectives

Compare and contrast different types of polymorphisms.
Define RFLP and its use in genetic mapping, parentage testing, and human identification.
Describe STR structure and nomenclature.
Relate STR use in parentage testing and gender identification (amelogenin locus).
Explain matching probabilities and allele frequencies in matching.
Describe Y-STR use in forensic and lineage studies.

Linkage Analysis

Family Histories: Analyzing multiple generations of affected individuals for shared STR alleles.
Population Studies: Identifying STR alleles common in certain populations or ethnic groups.
Sibling Analyses: Determining the likelihood of relatedness between individuals by analyzing shared alleles.
Mapping Genes: Using STRs as markers to pinpoint the location of genes involved in diseases.

Bone Marrow Engraftment Testing

Alleles: The unique genetic characteristics (alleles) of DNA in recipient and donor.
Quality Assurance: Ensures the integrity and accurate identification of tissue in surgical specimens.

Single Nucleotide Polymorphisms

Definition: Variations in the nucleotide sequence affecting a single base.
Importance: Used in genetic and disease mapping and for forensic studies.
Frequency: Relatively common, with one SNP observed every 300 nucleotides in the human genome.
Identification: Detected by direct sequencing, using next-generation methods.

HapMap Project

Objective: Mapping haplotypes— sequences of SNPs commonly inherited together.
Methodology: Sequencing DNA to detect common SNPs, then identifying haplotype blocks.
Significance: Used to identify disease-related genes, for improving understanding of human ancestry.

Mitochondrial DNA Polymorphisms

Circular genome, 16,569 base pairs.
Maternal inheritance.
Variations in the hypervariable regions (HV1 and HV2) offer high resolution in identification.
Used in forensic comparisons, ancestry studies, and disease research.

Advanced Concepts

Matching Profiles: Using the frequency of alleles in the population to evaluate matching odds.
Linkage Analysis: Establishing a connection between an STR marker and a trait or disease.
Chimerism: Presence of two or more distinct genetic populations in one individual (e.g. after a stem-cell transplant).
Paternity and Sibship Testing: Determining the likelihood of a stated relationship using allele frequencies and shared alleles or the absence thereof.
STR nomenclature: System by which STR loci are named.
Quantitative Methods in Engraftment Testing: Measuring the proportion of donor/recipient peak heights to identify engraftment.
Epigenetic Analysis: Examining DNA methylation changes to detect differences in individuals or groups.

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Description

This quiz covers various aspects of forensic genetics, including microvariant alleles, genetic loci, and the role of Standard Reference Material from the National Institute of Standards and Technology. Enhance your understanding of how genetic profiles are interpreted in forensic contexts.