Advanced review of modern DNA profiling and its application in forensic science.
Key Topics:
Take this exam in our timed interactive simulator to track your performance and get detailed analytics.
What are the three primary components that make up a single DNA nucleotide?
A deoxyribose sugar, a phosphate group, and a nitrogenous base
According to the fundamental principles of DNA structure, a single nucleotide consists of a deoxyribose sugar molecule, a phosphate group, and a nitrogenous base. Source: DNA Structure: Nucleotides.
In a double-stranded DNA molecule, which of the following represents the correct complementary base pairing rules?
Adenine pairs with Thymine; Cytosine pairs with Guanine
Chargaff's rules state that in DNA, Adenine (A) always pairs with Thymine (T), and Cytosine (C) always pairs with Guanine (G). Source: DNA Structure: base pairing (A-T, C-G).
If a forensic scientist discovers a DNA sequence that reads 5'-A-T-G-C-C-A-3', what would the complementary strand's sequence be?
3'-T-A-C-G-G-T-5'
Following complementary base pairing rules, A pairs with T and C pairs with G. Thus, A-T-G-C-C-A pairs with T-A-C-G-G-T. Source: DNA Structure: base pairing.
How many pairs of chromosomes are found in the nucleus of a normal human somatic cell?
23
Human somatic cells contain 23 pairs of chromosomes, totaling 46 chromosomes. These contain the nuclear DNA inherited from both parents. Source: DNA Structure: chromosomes.
Which statement best describes the inheritance pattern of nuclear DNA compared to mitochondrial DNA?
Nuclear DNA is inherited from both parents, whereas mitochondrial DNA is inherited maternally.
Nuclear DNA is a combination of genetic material from both the biological mother and father. Mitochondrial DNA (mtDNA) is inherited exclusively from the mother. Source: Nuclear DNA vs. Mitochondrial DNA.
A forensic anthropologist unearths severely degraded skeletal remains exposed to environmental elements for over 50 years. What type of DNA analysis is most likely to yield a successful profile?
Mitochondrial DNA (mtDNA) analysis, because there are hundreds of copies of mtDNA per cell.
Mitochondrial DNA is highly abundant (hundreds to thousands of copies per cell) compared to the single set of nuclear DNA per cell. It is extremely useful for degraded remains or hair shafts. Source: Mitochondrial DNA (useful for degraded remains).
A suspect drops a hair at a crime scene. Upon microscopic examination, the hair shaft is present, but the follicular tag (the root) is completely absent. Which type of DNA can be successfully recovered and analyzed from this evidence?
Only mitochondrial DNA
The follicular tag contains cellular material rich in nuclear DNA. Without the root, the keratinized hair shaft primarily retains mitochondrial DNA, making mtDNA analysis the only viable option. Source: Mitochondrial DNA.
What is the primary function of the Polymerase Chain Reaction (PCR) in forensic science?
To exponentially amplify tiny or trace amounts of specific DNA sequences for analysis.
PCR acts as a 'molecular photocopier' to amplify minute amounts of target DNA exponentially so that enough is available for profiling. Source: Extraction & Amplification: The steps of PCR.
The first step of the Polymerase Chain Reaction (PCR) cycle involves heating the sample to approximately 94-95 degrees Celsius. What is the name of this step and its molecular purpose?
Denaturation; it breaks the hydrogen bonds separating the double-stranded DNA into single strands.
Denaturation is the first step of PCR, involving high heat (typically 94-95°C) to break the hydrogen bonds between the base pairs, producing single-stranded DNA templates. Source: The steps of PCR - denaturation.
During the second stage of a PCR cycle, the temperature is lowered to around 50-65 degrees Celsius. What crucial event happens during this 'annealing' phase?
Short, synthesized single-stranded DNA sequences called primers bind to specific complementary target sequences on the DNA template.
During the annealing phase, the temperature is reduced so that primers (short DNA sequences designed to target specific loci like STRs) can successfully attach to the separated DNA strands. Source: The steps of PCR - annealing.
