GENERAL QUESTIONS 1. DNA profiling is also useful in taxonomic (classification),
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GENERAL QUESTIONS 1. DNA profiling is also useful in taxonomic (classification), conservation, and evolutionary studies Briefly explain how DNA profiling is used in each of these fields. a. Taxonomy b. Conservation c. Evolution Restriction enzymes are isolated from bacteria. Why do bacteria have restriction enzymes and how do they protect their own DNA from being chopped up? 2. 3. Assume a crime has been committed. Bodily fuids have been found that may link a suspect in the case to the crime. Describe the handling of DNA from the crime scene to the lab where it will be analyzed so as to prevent contamination from other sources of DNA. What might these other sources be?Explanation / Answer
1 a. Taxonomy: DNA profiling involves employing various molecular biology techniques to identify differences in the DNA sequences and classify organisms based on these differences. Thus the ecology and evolution of organisms are well studied and characterised based on the classification by DNA profiling. Differences in the DNA or polymorphisms can be as simple as single nucleotide changes at a given nucleotide position or varying number of tandem repeats or presence of repetitive elements, resulting in complex polymorphisms. Species or population-specific simple or complex DNA polymorphisms are used to generate fingerprint patterns particular to particular individuals or population, thus facilitating classification.
b. Conservation: A good example of the usefulness of DNA profiling in conservation would be identifying genetic markers that can distinctly identify different shark species. Each DNA fingerprint pattern is unique to each shark. In fact low cost tests have been devised employing these markers that can identify the shark species killed for a particular shark fin soup. Such efforts have easily allowed identification of illegal fishing and trade of processed shark products, thus preventing exploitation of protected shark species. Additionally DNA profiling can be done from detached body parts or organs or from processed shark products.
c. Evolution: Genetic variation in natural populations have been easily traced with DNA profiling, while multi-locus profiles have been extensively studied to determine species-hybrid. Comparative genomics of entire genomes of concerned species will reveal the conserved overlapping sequences as well as the differences that determine the relatedness between the species on an evolutionary time scale.
2. Bacteria have restriction enzymes such that they can be used on foreign DNA, thereby protecting themselves. But along with expressing these restriction endonucleases, bacteria also express methyl transferases like Dam and Dcm that methylates DNA at particular motifs or sequences such that the host DNA sequence is prevented from being degraded or chopped off by restriction endonucleases. The restriction enzymes thus cleaves the same DNA sequence if not methylated as obtained from foreign DNA like bacteriophages.
3. Bodily fluids like blood, saliva, semen are important source of DNA, which upon proper analyses can help identify a suspect related to the crime. Proper collection, storage and documentation of the DNA samples should be done. Liquid items should be stored in collection tubes and refrigerated. Biological evidences should be air-dried and not exposed to direct sunlight before packaging into appropiate collection bags. Paper bags are preferred as pastic bags retain moisture and can allow growth of molds. Such evidences should be stored in cool and dry conditions. Stains should be photographed with or without scale, carefully swabbed, air-dried and packaged.
DNA contamination in crime scenes can happen in a variety of ways. Exogenous DNA can get intriduced into biological samples by sneezing, coughing over the evidence. It may also happen if samples get mixed during DNA profiling. Drops of sweat can also be a source of contamination. Contamination during handling may occur during DNA handling in lab and may come from the analyst or lab personnels, contamination from the allelic ladder, or from multiple batches of DNA being handles at once.
4. Positive aspects: The police will be benefited from the DNA data bank, allowing them to clear crimes faster and saving time. As DNA fingerprint pattern will be unique to each individual, it will be serve as an unique identity. Terrorists and criminals wont be able to use false papers/visas/passports, as their DNA profile will be matched.
Negative Aspects: Creating and maintaining a DNA data bank is expensive. The information will have restricted access. Additionally, if the same information falls into the hands of corrupt officials who can easily sell it off to unauthorised individuals.
5. Non-coding regions of the DNA are transcribed but not translated . They are home to the complex polymorphism examples discussed previously. These regions have repetitive elements, that is multiple copies of the same sequence. These regions are not under selective pressure and are prone to variation, that is mutation or crossover rates are high. Individuals vary in the number of tandem repetas or these interspersed repetitive elements, and therefore these turn out to be unique signatures for individuals belonging to same species or closely related species. Coding regions on the contrary may have single nucleotide polymorphisms that lead to silent or missense mutations. In the former case, changes do not change the resulting amino acid, due to wobbling of the third base of the codon. In the latter case, mutation results in amino acid change which may be harmless as the resultant protein structure and function remains unchanged or may be harmful like in sickle cell anemia.
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