(DNA) DNA Analysis Module Overview

DNA Analysis Module Overview 

DNA is the genetic code of life. What makes us "human" is the number and sequence of nucleotides in our genome. The human genome, as well as the genome of many other species, has been sequenced. While 99.9% of the genes in every human are the same, the 0.1% variation makes each individual unique. When these small but unique parts of an organisms genome is known, it is possible to identify an unknown species by comparing the DNA sequence of the unknown to the known and make a match.

Essential Questions

    1. How is DNA evidence analyzed?
    2. What makes DNA evidence unique?
    3. How can old or degraded samples be analyzed for DNA?
    4. How are DNA profiles stored?

Key Terms

  1. Chromosome - The biological structure by which hereditary information is physically transmitted from one generation to the next. Located in the cell nucleus, it consists of a tightly coiled thread of DNA with associated proteins and RNA. The genes are arranged in linear order along the DNA.
  2. Autosomal Chromosome - Any chromosome that is not a sex chromosome.
  3. Sex Chromosome - Either of a pair of chromosomes, usually designated X or Y, in the germ cells of most animals and some plants, that combine to determine the sex and sex-linked characteristics of an individual. XX results in a female and XY in a male in mammals.
  4. Gene - The basic unit of heredity a functional sequence of DNA in a chromosome.
  5. DNA - (Deoxyribonucleic Acid) Often referred to as the "blueprint of life", DNA is the genetic material present in the nucleus of cells which is inherited half from each biological parent. DNA is a chemical substance contained in cells, which determines each person's individual characteristics. An individual's DNA is unique, except in cases of identical twins.
  6. Purines - Nitrogenous base (adenine or guanine) that is a constituent of DNA or RNA.
  7. Pyrimidines - Nitrogenous base (cytosine, thymine, or uracil) that is a constituent of DNA or RNA.
  8. Complementary Base Pairing - A,T,C and G are molecular building blocks of DNA that only continue in specific "base" pairs, e.g., A only pairs with T, and C only pairs with G.
  9. Hydrogen Bonds - A chemical bond in which a hydrogen atom of one molecule is attracted to an electronegative atom, especially a nitrogen, oxygen, or fluorine atom, usually of another molecule.
  10. DNA Replication - A process in which DNA makes a copy of itself. This occurs inside our cells during a stage in the cell life cycle called interphase.
  11. Human Genome Project - A comprehensive effort by molecular biologists worldwide to map the human genome, completed in 2003. The resulting projection reflects the 3 billion DNA letters of the human genome with 99.99% accuracy.
  12. Short Tandem Repeats - (STR) Multiple copies of a short identical DNA sequence arranged in direct succession in particular regions of chromosomes.
  13. Loci - The specific physical location of a gene on a chromosome.
  14. CODIS - Combined DNA Index System. A collection of databases of DNA profiles obtained from evidence samples from unsolved crimes and from known individuals convicted of particular crimes. Contributions to this database are made through state crime laboratories and the data are maintained by the FBI.
  15. DNA Fingerprinting - Analyses of the lengths of the fragments reveal that when looking at multiple VNTRs within and between individuals; no two people have the same assortment of lengths. This technique became known to the public as "DNA fingerprinting" because of its powerful ability to discriminate between unrelated individuals.
  16. DNA Extraction - Removing DNA from any type of cell for the purpose of analysis.
  17. Polymerase Chain Reaction (PCR) - A process used in DNA identification testing in which one or more specific small regions of the DNA are copied using a DNA polymerase enzyme so that a sufficient amount of DNA is generated for analysis.
  18. Thermal Cyler - A laboratory device in which a polymerase chain reaction is carried out repeatedly in cycles which in turn amplifies the sample DNA segments. The instrument contains a thermal block which contains the DNA samples and can precisely control the internal temperature.
  19. Restriction Enzyme - A protein harnessed from bacteria that recognizes specific, short nucleotide sequences and cuts DNA at those sites.
  20. Gel Electrophoresis - A method of separating substances, especially proteins, and analyzing molecular structure based on the rate of movement of each component in an agarose gel while under the influence of an electric field.
  21. Variable Number of Tandem Repeats - (VNTRs) - Repeating units of a DNA sequence.
  22. Amelogenin Gene - A gene present on the X and Y sex chromosomes that is used in DNA identification testing to determine the gender of the donor of the DNA in a biological sample.
  23. Mitochondrial DNA- (mtDNA) - The DNA found in the many mitochondria in each cell of a body. The sequencing of mitochondrial DNA can link individuals descended from a common female ancestor.
  24. Recombinant DNA - Altered DNA resulting from the insertion into the chain, by chemical, enzymatic, or other biological means, of a sequence (a whole or partial chain of DNA) not originally (biologically) present in that chain.
  25. Splicing - To join together or insert (segments of DNA or RNA) so as to form new genetic combinations or alter a genetic structure.
  26. Bases - The four building blocks of DNA are called bases. The building blocks are Cytosine, Guanine, Thymine, Adenine and are commonly referred to as C, G, T, A.
  27. Capillary Electrophoresis - Narrow silica capillaries (or tubes) containing a polymer solution through which the negatively charged DNA molecules migrate under the influence of a high voltage electric field. Important advantages of the CE technique, compared to gel electrophoresis, include quicker and more easily automated analyses.
  28. CODIS Core Loci - Thirteen STR (short tandem repeat) sequences that have been selected for the Combined DNA Index System (CODIS).
  29. Cold Hit - When CODIS recognizes a match between an offender and forensic profile, it is referred to as a "cold hit"
  30. DNA Analysis - The process of testing to identify DNA patterns or types. In the forensic setting, this testing is used to exclude or include individuals as possible sources of body fluid stains (blood, saliva, semen) and other biological evidence (bones, teeth, hair). This testing can also be used to indicate parentage.
  31. DNA Profile - The result of determining the relative positions of DNA sequences at several locations on the molecule. Each person (except identical twins) has a unique DNA profile when used in the context of the CODIS database which evaluates 13 specific DNA locations.
  32. Exclusion - A DNA test result indicating that an individual is excluded as the source of the DNA evidence. In a criminal case, "exclusion" does not necessarily equate to "innocence".
  33. Forensic Hit - A CODIS match between two or more crime scene profiles.
  34. Genome - All the genetic material in the chromosomes of a particular organism its size is generally given as its total number of base pairs.
  35. Inclusion- (Failure to Exclude) - The inability to exclude an individual as a possible source of a biological sample. This occurs when all types from a specific location in the DNA of a known individual are also present in the types for that specific location in the DNA obtained from an evidence sample.
  36. LDIS - The Local DNA Index System of CODIS which uploads forensic and offender DNA profiles to the State DNA Index System, or SDIS.
  37. National DNA Index System (NDIS) - Authorized by the DNA Identification Act of 1994, the FBI administers this national index. NDIS compares DNA profiles associated with a crime scene to DNA profiles collected from known convicted offenders, as well as to other crime scene profiles. When the DNA profiles are uploaded to NDIS, they are searched against the other DNA profiles submitted by other participating states.
  38. Offender Hit - A CODIS match between a crime scene profile and an offender profile.
  39. SDIS - State DNA Index System containing the state-level DNA records uploaded from local laboratory sites within the state. SDIS is the state's repository of DNA identification records and is under the control of state authorities. The SDIS laboratory serves as the central point of contact for access to NDIS. The DNAUI serves as the SDIS laboratory for the FBI.

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