DNA and Genetics Basics
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1
What is deoxyribonucleic acid or DNA?
A molecule composed of nucleotide chains that stores and transmits genetic information in living organisms.
2
What are the four nitrogenous bases found in DNA?
Adenine, thymine, guanine, and cytosine.
3
What is complementary base pairing in DNA?
Adenine pairs with thymine, while guanine pairs with cytosine.
4
What type of bonds hold complementary DNA bases together?
Hydrogen bonds.
5
What forms the structural backbone of a DNA strand?
Alternating deoxyribose sugars and phosphate groups joined by phosphodiester bonds.
6
What does antiparallel mean in DNA structure?
The two strands of the DNA double helix run in opposite 5-prime to 3-prime directions.
7
What is a chromosome?
A DNA molecule organized with associated proteins that carries genetic information.
8
How many chromosomes are normally present in a human diploid somatic cell?
46 chromosomes arranged in 23 pairs.
9
How many chromosomes are normally present in a human haploid gamete?
23 chromosomes.
10
What is an autosome?
A chromosome other than a sex chromosome.
11
What is a gene?
A DNA sequence that contributes to the production of a functional RNA or protein product.
12
What is a locus in genetics?
A specific position or region on a chromosome.
13
What is an allele?
An alternative form or sequence variant at a genetic locus.
14
What is a genotype?
The genetic constitution of an individual at one or more specified loci.
15
What is a phenotype?
An observable characteristic resulting from genetic, environmental, and other influences.
16
What is homozygosity?
The presence of two identical alleles at a particular autosomal locus in a diploid individual.
17
What is heterozygosity?
The presence of two different alleles at a particular autosomal locus in a diploid individual.
18
What is Mendel's law of segregation?
The principle that the two alleles at a locus separate during gamete formation so each gamete ordinarily receives one allele.
19
What is a short tandem repeat or STR?
A DNA region containing a short nucleotide sequence repeated consecutively a variable number of times.
20
Why are STR loci useful in forensic human identification?
They are often highly variable among individuals and can be analyzed using small quantities of DNA.
21
What is an STR allele designation?
A standardized label generally reflecting the number of repeat units at a particular STR locus.
22
What is a microvariant STR allele?
An STR allele containing a partial repeat or other variation represented by a designation such as 9.3.
23
What is a multiplex PCR assay?
A polymerase chain reaction that amplifies multiple target DNA regions in one reaction.
24
What is the purpose of PCR denaturation?
To separate double-stranded DNA into single strands by disrupting hydrogen bonding.
25
What is the purpose of PCR annealing?
To allow primers to bind to complementary sequences on the target DNA.
26
What is the purpose of PCR extension?
To allow DNA polymerase to synthesize new DNA strands from the primers.
27
What is a PCR primer?
A short nucleic acid sequence that binds a target region and provides a starting point for DNA synthesis.
28
What is thermostable DNA polymerase?
An enzyme that synthesizes DNA and retains sufficient activity through repeated high-temperature PCR cycles.
29
What is a PCR inhibitor?
A substance that interferes with DNA amplification and may reduce or prevent recovery of a usable profile.
30
What is quantitative PCR or qPCR used for in forensic DNA analysis?
To estimate amplifiable DNA quantity and sometimes assess degradation or inhibition before STR profiling.
31
What is capillary electrophoresis in forensic DNA analysis?
A technique that separates fluorescently labeled DNA fragments according to their electrophoretic behavior, principally related to size.
32
What is an electropherogram?
A graphical display of detected DNA fragment signals, often showing fluorescence peaks by fragment size or migration position.
33
What is an allelic ladder?
A reference mixture of known STR alleles used to support accurate allele designation.
34
What is a stutter peak in STR analysis?
A PCR artifact typically appearing near a true allele because of strand slippage during amplification.
35
What is allele dropout?
Failure to detect an allele that is actually present in a DNA sample.
36
What is allele drop-in?
The appearance of an unexpected allele signal not attributable to the true contributors, often associated with contamination or stochastic effects.
37
What is a low-template DNA sample?
A sample containing a small amount of amplifiable DNA, often increasing the risk of stochastic variation and incomplete profiles.
38
What is a partial DNA profile?
A profile in which usable results are obtained for only some of the targeted genetic loci.
39
What is a mixed DNA profile?
A DNA profile containing genetic contributions from two or more individuals.
40
What is a major contributor in a DNA mixture?
A contributor whose DNA generally accounts for a relatively larger proportion of the observed profile.
41
What is a minor contributor in a DNA mixture?
A contributor whose DNA generally accounts for a relatively smaller proportion of the observed profile.
42
What is the random match probability or RMP?
The estimated probability that a randomly selected unrelated individual from a specified population would possess a particular DNA profile.
43
What is the product rule in DNA profile statistics?
A method of combining appropriate locus-specific genotype probabilities to estimate a multilocus profile probability, subject to relevant assumptions.
44
What is a likelihood ratio in forensic DNA interpretation?
A comparison of how probable the observed DNA evidence is under two specified competing propositions.
45
What is probabilistic genotyping?
The use of statistical models to evaluate DNA profile data, including complex mixtures, while accounting for relevant sources of variation.
46
What is a Y-STR profile?
A DNA profile based on short tandem repeat loci located on the Y chromosome.
47
Why do Y-STR profiles have limited power to distinguish close paternal relatives?
The Y chromosome is generally transmitted along paternal lineages with relatively few changes between generations.
48
What is mitochondrial DNA inheritance?
Transmission of mitochondrial DNA predominantly through the maternal line.
49
Scenario: A child's autosomal STR genotype is 12,15 and the mother's genotype is 12,14. Which allele must ordinarily have come from the biological father?
Allele 15, assuming conventional Mendelian inheritance and no relevant mutation or analytical error.
50
Scenario: A DNA profile matches a suspect at all tested STR loci. Does this alone prove the suspect committed the crime?
No. The result must be interpreted using appropriate statistics and the circumstances of DNA deposition, transfer, persistence, and recovery.
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