Chapter 11: DNA Analysis Flashcards
What are the four bases that make up human DNA?
The four bases (nucleotides) that make up DNA are adenine, guanine, thymine, and cytosine. They are deoxyribose molecules. A-T bond together, and G-C bond together.
What is a gene?
A gene is a section of a chromosome that provides instructions to manufacture proteins. The instructions are copied into RNA that transmits the information to protein manufacturing sites in the cell. All human characteristics are defined and controlled by genes.
What is an allele?
An allele is a form of a particular gene at a particular locus in the genome. For example, red, brown, or blonde hair are all alleles for hair colour.
List three ways that mitochondrial DNA differs from genomic DNA?
First, cells contain many mitochondria, and each one has up to 10 copies of mtDNA. Each cell thus contains hundreds or thousands of copies of mtDNA, whereas there are only two copies of genomic DNA in a cell.
Second, all male and female mtDNA comes from the mother. In genomic DNA, one half comes from each parent.
Third, mtDNA shows a high degree of variation between unrelated people, but there are only two hypervariable regions in mtDNA. Genomic DNA is much more discriminating.
What is a restriction enzyme? In what kind of DNA typing is it used?
A restriction enzyme is an enzyme that is used to isolate small fragments of DNA. It is often used in RFLP, restriction fragment length polymorphism.
What are some of the advantages of DNA typing over other methods of identifying a person, such as fingerprints?
There is a standard database called Combined DNA Index System (CODIS) that can make it very easy to identify who the sample belongs to. Also, due to PCR, even super tiny fragments can be helpful in typing a person.
In one of the early DNA typing cases in England, the police went to all males in a town to collect DNA samples to be tested against crime scene evidence. What are the problems with such an approach?
Firstly, if the area is a place many townspeople frequent, it could result in one’s wrongful conviction just for some of their DNA being present. Second, the person who committed the crime may have left town.
Third, it is a waste of resources.
What does PCR stand for? For what purpose was it developed?
PCR stands for polymerase chain reaction. Its purpose is to make copies (amplify) DNA using polymerase enzymes. It began because RFLP methods required a substantial amount of DNA quantities, but it was often hard to come by. PCR allowed us to duplicate DNA to create many copies for analyzing and doing tests on.
What is an STR? Why has it become the method of choice for forensic DNA typing?
An STR is a short tandem repeat. They consist of 2-6 base pairs that have been segmented by restriction enzymes. They are also known as microsatellites. They contain repeating units of base pair sequences in tandem. They are preferred over VNTRs because they exhibit high variability in a population, which gives a high degree of accuracy when associating evidence with a suspect. They also are less sensitive to degradation of DNA due to their size. Finally, there are many microsatellites to choose from.
What is the importance of Amelogenin?
Amelogenin are a locus on each of the sex determination chromosomes. The region is six base pairs longer in males than in females. It can be used to determine the sex of an individual. Female chromosomes will show a single band on each chromosome. Male chromosomes will show two bands, due to the Y chromosome having a longer region.
What is a polymarker? How is it typed?
A polymarker is a gene that exhibits sequence polymorphisms. An example would be DQ alpha (DQA1), which is typed using a method called reverse blot dot.
What is a reverse dot blot? How is it used in DNA typing?
A reverse dot blot is a process that involves identifying particular alleles present by reacting them with colour-forming reagents on nylon strips. They are no longer used in forensic science.
Of the DNA testing methods you have learnt about in this chapter, which one has the potential of generating a profile that can be considered to be unique? How is this possible?
STRs exhibit high variability in a population which can generate a profile that can be considered to be unique.
What types of electrophoresis are used for the separation of DNA fragments in STR analysis?
In STR analysis, modern practice employs capillary electrophoresis, which uses a capillary filled with a polymer similar to polyacrylamide. The DNA is detected by laser-induced fluorescence. The alleles are divided into 4-5 groups, and each group is labeled with a different colour fluorescent dye. The dyes are then detected by a UV/visible detector. There will then be one or two peaks (homozygous or heterozygous) for each locus. Allelic ladders are used for calibration.
What is Taq polymerase? How is it used in DNA typing?
Taq polymerase is a common enzyme used in PCR. It is used to add single bases to the primer, one-by-one, during the extension phase of PCR. It helps grow complementary strands.
