FINALS LEC: DNA POLYMORPHISM & HUMAN IDENTIFICATION Flashcards
Variations of DNA sequences (ranging from a single base pair to thousands of base pairs) that are shared by 1%-2% or more of a given population
POLYMORPHISM
Highly repeated sequences (6-8kbp in length), containing RNA polymerase promoters & open reading frames
Long interspersed nucleotide elements (LINES)
Highly repeated sequences approximately 0.3 kbp in length, including Alu elements
Short interspersed nucleotide elements (SINES)
Head-to-tail repeats of DNA sequences with <10-bp repeat units
Short tandem repeats (STRs)
Head-to-tail repeats in DNA with 10-50-bp repeat units
Variable-number tandem repeats (VNTRs)
A sequence variation that results in creating, destroying, or moving a restriction site
Restriction fragment length polymorphisms (RFLPs)
are A.K.A. mobile elements/transposable elements/transposons
LINES & SINES
is used to form patterns by breaking down DNA
RFLP
Differences in sizes & number of fragments generated by restriction enzyme digestion of DNA
Restriction Fragment Length Polymorphisms (RFLPs)
RFLP typing in humans required the use of ____
Southern blot technique
Only the fragments with complementary sequences to a probe to the B region (top) can be visualized
>2,000 RFLP loci have been described in human DNA
Restriction Fragment Length Polymorphisms (RFLPs)
The uniqueness of the collection of
polymorphisms in each individual is the basis for human ID at the DNA level. t or f?
true
RFLP protocols for human ID:
▪ Sources of genomic DNA:
blood, saliva, or tissue
RFLP protocols for human ID:
North American Labs:
HaeIII restriction enzyme
RFLP protocols for human ID:
European labs:
HinfI restriction enzyme
Regulation of results from independent labs:
Standard Reference Material (SRM) DNA Profiling Standard for RFLP analysis (1992)
Polymorphisms can be used as landmarks/markers in the genome to determine the location of other genes
Genetic Mapping with RFLPs
More frequently a particular polymorphism is present in
persons with a disease phenotype = more likely an affected gene is located close to the polymorphism
Genetic Mapping with RFLPs
Inherited breast cancer:
RFLP location
BRCA1 gene
RFLP location:
17q21
BRCA1 gene:
mapped to this position
Fragment sizes of an individual are a combination of those from each parent
RFLP & PARENTAGE TESTING
alleles/fragment sizes of the child & the mother are analyzed
Paternity test
provide the remaining alleles/fragments (inclusion)
Alleged fathers (AFs)
1st genetic tool for human ID:
ABO blood group antigens
1st human DNA profiling/fingerprinting system:
UK Forensic Science Service (1985) using Sir Alec Jeffrey’s Southern blot multiple-locus probe (MLP)RFLP system
Single-locus probe (SLP) (1990) in Europe & N. America
HUMAN ID USING RFLPs
Requires 0.7% gels
HUMAN ID USING RFLPs
RFLP Southern blot technique:
100 ng to 1 ug of DNA (1-20 kbp)
HUMAN ID USING RFLPs
Results:
5-7 days
Head-to-tail repeats of DNA sequences with <10-bp repeat units
Short Tandem Repeats (STRs)
Detection Method of Short Tandem Repeats (STRs)
PCR
used to determine the no. of repeats in the locus by the size of the amplicons
Allelic ladders
Specimen required for Short Tandem Repeats (STRs):
10 ng (key factor for forensic analysis
Analysis of Short Tandem Repeats (STRs):
Fluorescent detection systems (capillary electrophoresis)
Analysis time of Short Tandem Repeats (STRs):
24-48 hours
(microsatellites or simple sequence repeats) are short tandemly repeated DNA sequences of 1-6 bp in a DNA sequence
Short tandem repeat
is a sequence of two or more DNA bases that is repeated many times in a head-to-tail manner on a chromosome.
tandem repeat
STR within genes:
according to gene name
intron 1 of human tyrosine hydroxylase gene on chromosome 11
TH01
lintron 10 of human thyroid peroxidase gene on chromosome 2
TPOX
test subject is the father/not
Paternity test
likelihood of paternity
Paternity index
summarizes & evaluates the genotype information
Combined paternity index (CPI)
CPI = 5.719 x 8.932 x 15.41 x 10.22 = 8,044.931
Indicate that the child is 8,045x more likely to have inherited the 4 observed alleles from the AF than from another man
5 STR & Sibling Tests
Full-sibling test
Half-sibling test
Kinship index/sibling index/combined sibling index
Avuncular testing
Probability of relatedness
likelihood that 2 people tested share a common mother & father
Full-sibling test
likelihood that 2 people tested share 1 common parent
Half-sibling test
likelihood ratio
Kinship index/sibling index/combined sibling index
2 alleged relatives are related as either an aunt/uncle of a niece/nephew
Avuncular testing
based on the no. of shared alleles between the tested individuals
Probability of relatedness
▪ STR located on the Y chromosome, paternally related men share all Y loci
▪ Represented only once per genome & only in males
▪ Applications: forensic, lineage, population studies, kinship testing
Y-STR
2 or more males have a common paternal ancestors
Y-STR/paternal lineage test
group of males having the same surnames is expected to be related to a common male ancestor, sharing the same Y-chromosome alleles
Surname test
Single-nucleotide differences (1-bp)
Single-Nucleotide Polymorphisms (SNPs)
human nucleotide sequence differs every 1,000-1,500 bases from 1 individual to another
HGP
2 haploid genomes differ at 1 nucleotide per 1,331 bp ❖ 11 million sites in genome of 3 billion bp that vary in at least 1% of the world’s population = 11 million SNPs in each individuals
International SNP Map Working Group
▪ Genetic mapping, disease production, and human ID
▪ Detection: direct sequencing
▪ Approx. 10 millions SNPs have been identified (99% have no biological effects; over 60,000 within genes; some are associated with disease)
▪ Classification: according to location, relation to coding sequences, & whether they cause a conservative/nonconservative sequence alteration
SNPs
Contribute to individual differences in function & susceptibility to various diseases such as Parkinson disease, Alzheimer disease, bipolar disorder, & cancer
MITOCHONDRIAL DNA POLYMORPHISMS
Amino acid variations
PROTEIN BASED ID
• Epigenetic alterations (DNA methylation)
• Result of environmental events: Profile is unique = no 2 individuals will have the same environmental exposures
EPIGENETIC PROFILES