Lecture 13: DNA Analysis Flashcards
Who discovered the configuration of the DNA molecule?
James Watson and Francis Crick in 1953
Rosalind Franklin contributed to the discovery through her X-ray diffraction work.
What is DNA fingerprinting and who developed it?
developed by Alec J. Jeffrey in 1984 by isolating DNA markers
He was studying the gene of myoglobin.
Who won the Nobel Prize in Physiology or Medicine in 1962?
James Watson and Francis Crick
They were awarded for their discovery of the DNA structure.
What significant technique did Kary Mullis develop in 1985?
polymerase chain reaction testing
PCR stands for Polymerase Chain Reaction.
When did the FBI start DNA casework?
1988
What does DNA stand for?
Deoxyribonucleic acid
What are the four types of bases in DNA?
- A (adenine)
- C (cytosine)
- G (guanine)
- T (thymine)
What is the base-pairing rule for DNA?
- Adenine (A) binds with Thymine (T)
- Cytosine (C) binds with Guanine (G)
What is a chromosome composed of?
Genes with DNA made up of 2 strands of polymers of nucleotides
How many base pairs are in the human genome?
Approximately 3 billion
What is the probability of two different people having the same DNA profile?
1 in 113 billion
What are the two types of repeating DNA sequences looked for by forensic scientists?
- Variable Number Tandem Repeats (VNTRs): 6-100 base pairs
- Short Tandem Repeats (STRs): Short sequences of 2-6 bases
- Analyzed for tissue and inheritance matching
What is a polymorphism in DNA?
- Variations in length or base sequence
- Due to point mutations, insertion/deletion mutations
What is the advantage of using STRs over VNTRs in DNA profiling?
- Shorter lengths
- Less time required
- Smaller sample size needed
- Less susceptible to degradation
What is the minimum amount of DNA required for optimal DNA profiling?
1 ng (10-9 g)
How can DNA evidence be contaminated?
- Sneezing or coughing on evidence
- Touching face and then evidence
- Scene personnel deposition of trace materials
- Wind carrying contaminants
What is the role of PCR in DNA analysis?
It acts as a DNA photocopier
DNA collected from SOC are in a minute amount, insufficient for DNA fingerprinting
What is gel electrophoresis used for?
- Electric current sorts DNA molecules by size
- Smaller/lighter molecules move the furthest on the gel
- Measures the number of DNA repeats
How many core STR loci does the FBI use in DNA profiling?
13 core STR loci + 7 additional
The greater the number of STR loci is used on a
DNA fingerprint, the greater the accuracy of the
DNA fingerprint.
What are the advantages of using mitochondrial DNA (mtDNA)?
- Single-cell sensitivity
- Establishing kinship (complement of
mtDNA is maternally inherited) - Analyzing shed hairs and burnt remains
What are some disadvantages of using mitochondrial DNA?
- High contamination risk
- Heteroplasmy (more than one
mtDNA type in tissues) - Lower power of discrimination among maternal relatives
What are common problems encountered with DNA profiling?
- Partial profiles
- Mixed profiles
Why is DNA used as forensic evidence?
- Stability
- Identical all over body
- Unique
Describe the structure of DNA
- Composed of nucleotides
- Deoxyribose sugar, phosphate group, nitrogen-containing base
Describe the variation among individuals
- Most of human genome is the same
- Variation found in noncoding DNA
What is noncoding DNA?
- Do not encode protein sequences
- Usually in the form of repeated base sequences
How is DNA extracted?
- Centrifugation
- Agitation (break cell in buffer solution)
- Removal of protein, RNA, lipids
How does PCR work?
- Cycles through high and low temp (90/55/70°C)
- 90°C: hydrogen bonds between DNA strands break
- 55°C: synthetic DNA fragments added
- 70°C: DNA polymerase
What is the importance of paternity in DNA analysis?
A child inherits two genes, one gene from the
mother and one gene from the father
