Inheritance Patterns in a Population

Inheritance Patterns in a Population Definition of DNA sequencing DNA sequencing is a laboratory technique used to determine the exact sequence of bases (A, C, G, and T) in a DNA molecule. The DNA base sequence carries the information a cell needs to assemble protein and RNA molecules. DNA sequence information is important to scientists investigating the functions of genes. Technologies that are used in DNA sequencing. The technologies that are used in DNA sequencing include the use of enzymes to either fragment DNA (nucleases) or make copies of pieces of DNA (polymerases), the separation of DNA fragments by using gel electrophoresis or nanopores, and labelling bases for identification by using radioisotopes or fluorescent. How DNA sequencing is used to identify inheritance patterns in a population. Once the sequence of bases are known for the entire genome, the extent, location and role of variations in the base sequence can be determined. A single nucleotide polymorphism may be detected in individuals suffering a specific disease so the mutation that causes the disease may be identified. • Inheritance: if it occurs within a family and is passed from one generation to the next. You may compare their DNA sequence with the DNA sequence of a family that is know 100% for sure not to have that disease for example. Method for DNA sequencing For more reading: https://www.sigmaaldrich.com/technical-documents/articles/biology/sangersequencing.html Difference between DNA sequencing and DNA profiling. DNA sequencing includes the use of technologies to determine the sequence of nitrogenous bases in the genome of an organism, population or species. DNA profiling is the use of parts of DNA of an individual that are highly variable to match them for the purposes of determining identity or relationships. Research task: find similarities and differences between the two. Pros and cons for each method. Technologies used in DNA profiling. Technologies used in DNA profiling include the use of nucleases to break DNA into useful comparable segments, gel electrophoresis, the polymerase chain reaction, and labelling to detect and compare the progression of separated DNA segments. Method for DNA Profiling The system of DNA profiling used today is based on polymerase chain reaction (PCR) and uses simple sequences or short tandem repeats (STR). The DNA fragments that result are then separated and detected using electrophoresis. 1. Extraction: DNA is located within the nucleus of cells throughout the body and the extraction step is responsible for breaking open the nucleus and releasing the DNA molecules into solution. During this step it is also possible to separate the DNA molecules from all other cellular material and any other debris that may be present in a particular biological sample. Some of these materials can be potential “inhibitors” to steps later on in the DNA testing procedure so it is important to try and isolate only the DNA molecules. Common inhibitors commonly found in forensic cases are hemoglobin and indigo dyes from denim. Two common methods of extraction used at the BCA are a manual Phenol-Chloroform (otherwise known as Organic Extraction) and through the use of a robotic system called the Maxwell. Running samples on the Maxwell® 16 takes a minimum of two hours and samples extracted manually using the Phenol-Chloroform method takes a minimum of three hours. 2. Quantitation: One of the standards all DNA testing laboratories must meet is to ensure that the DNA recovered from an extraction is human rather than from another source such as bacteria. This is done through quantitation where the quality and quantity of DNA present in a sample is measured and assessed. Additionally, determining the amount of DNA in a sample is essential for success in the next step since most amplification systems require a narrow range of input DNA. This step is completed at the BCA through the use of a purchased Quantifiler DNA Human Quantification Kit and then running all samples on an instrument known as the ABI PRISM 7500 Sequence Detection System. This process takes approximately 30-60 minutes to set-up and then approximately two hours to run on the instrument. 3. Amplification: DNA amplification is accomplished through the use of a technique known as Polymerase Chain Reaction (PCR). PCR is a process in which millions of copies of a specific sequence of DNA can be made in a matter of only a few hours. This is important for forensic DNA samples since the DNA often found at crime scenes is limited in both quantity and quality. This molecular “xeroxing” process is completed by precise heating and cooling of the samples in a thermal cycling pattern for approximately 28 cycles. The amplification kit used by the BCA amplifies 15 different regions of DNA as well as a sex-determining marker. The BCA uses a purchased AmpFlSTR Identifiler kit and then the samples are run on an instrument known as the GeneAmp PCR System 9700. This process takes approximately 15-30 minutes to set-up and then approximately three hours to run on the thermalcycler instrument. Process of PCR 4. Capillary Electrophoresis (CE): After the PCR reaction is completed it results in a large mixture of amplified DNA molecules which need to be separated in order to distinguish the various molecules from one another. This is accomplished through a process known as capillary electrophoresis. DNA molecules carry a negative charge and once an electric current is applied to the sample the molecules enter a very thin capillary filled with a gel-like polymer and migrate towards the positive anode at the other end of the capillary. The PCR products are then separated by size because the smaller DNA molecules will have an easier time migrating through the polymer than the larger DNA molecules. The data from this process is then collected on a computer attached to the CE instrument and then through the use of a software program a DNA profile is developed. The BCA uses an instrument called the ABI Prism® 3130 Genetic Analyzer which is capable of analyzing four samples at a time. Set-up for this step takes approximately 10 -15 minutes and each injection on the 3130 takes approximately 45 minutes How DNA profiling is used to determine inheritance patterns within a population. It has enables us to understand that offspring obtain half of their DNA from each parent. If one parent (e.g., the mother) is known, then the half of the DNA segments that do not match with the mother must match will the potential father for paternity to be confirmed.