DNA

1. Honors forensic Science DNA

2. I. DNA is identical in every cell in body • A. DNA can be left at a crime scene even if there is no blood • B. DNA can survive longer than a fingerprint. Has even been performed on Egyptian mummies

3. c. Can indicate familial relationships • i. Example – a Philippine case involved a murder conducted by two individuals. One was identified by an eyewitness, but the second one was not. DNA from spit at the scene helped to ID the second man. He was a brother to the first.

4. D. DNA evidence does not combine like blood evidence does.

5. II. DNA Collection • A. National Institute of Justice – where to find it • i. Fingernails, or fingernail pairings • Ii. Tissues, paper towels, napkins, cotton swabs, ear swabs • Iii. Toothpicks, cigarette butts, straws, anything else that might have been in contact with the mouth

6. Iv. Blankets, pillows, sheets, mattresses, dirty laundry • V. Head gear of any type • Vi. Eyeglasses, contact lenses • Vii. Used stamps, envelopes

7. Viii. Tapes, ropes, cords, anything else used as ligatures • Ix. Used condoms • X. Bullets that have passed through bodies

9. B. Collection Techniques – extra care must be taken to avoid contamination • i. Bring lots of gloves, and change them often • Ii. Where possible, use disposable tools • Iii. Avoid contact between gloved hands and face or hair

10. Iv. Don’t touch surfaces except with collection material • V. Wear a mask over mouth or refrain from sneezing or coughing • Vi. Samples must be air dried

13. III. What is DNA? • A. Gene = fundamental unit of heredity • i. They instruct the body cells to make protein that determine everything from hair color to our susceptibility to disease • Ii. Each gene is composed of DNA specifically designed to carry out a single body function

14. B. Structure deduced by Watson and Crick • C. Is a polymer • D. Units are called nucleotides

15. i. Composed of sugar – deoxyribose • Ii. Phosphate group • Iii. Nitrogen bases • 1. adenine • 2. cytosine • 3. thymine • 4. guanine

16. 5. adenine always pairs with thymine • 6. cytosine always pairs with guanine

17. E. Sugar and phosphates bond together to form a backbone • F. Bases form rungs of ladder • G. Double helix

18. IV. DNA at work • A. DNA directs the production of proteins • B. Proteins are made of amino acids

19. i. There are 20 common amino acids • Ii. Each amino acid is coded for by 3 bases • Iii. This code is not restricted to humans

20. V. Human genome • A. Scientists are working to unravel the human genome • B. Hope it will lead to cures for genetic diseases • C. Better understanding of role and implications of evolution

21. VI. Replication of DNA • A. Each strand in the double helix has the same information • B. DNA replication begins with the unwinding of the DNA strands in the double helix • C. Free nucleotides bind with single strand templates to form new double strand

23. VII. Polymerase Chain Reaction • A. A technique for replicating or copying a portion of a DNA strand outside a living cell • B. This technique leads to millions of copies of the DNA strand

24. C. Means that more testing can be done on the original DNA because not limited by sample size

25. VIII. Recombinant DNA • A. Relationship between the base letters on a DNA strand and the type of protein specified by the sequence of these letters is called the genetic code • B. Understanding what is produced by different sequence of bases has given rise to recombinant DNA technology

27. C. Relies on ability of certain chemicals (restriction enzymes) to cut DNA into fragments • D. Highly specialized “scissors” • E. Once DNA is cut other DNA can be inserted (usually bacterium)

28. F. Altered DNA is then passed on to descendants • G. Has enormous commercial potential • H. allows us to manipulate DNA • i. Possible treatments for disease • J. Plant genetic engineering

29. IX. DNA Typing • A. Restriction Fragment Length Polymorphisms (RFLP) • i. Portions of DNA has sequences of letters repeated numerous times • Ii. These “tandem repeats” offer a means to distinguish one individual from another

30. Iii. Within the world’s population there are numerous possibilities for the number of times a particular sequence of base letters can repeat themselves • Iv. The number of possibilities increases when consider two chromosomes

31. V. Restriction enzymes may be used to cut chromosomes into hundreds of fragments, some containing repeating sequences • Vi. Length differences that result from this process are Restriction Fragment Length Polymorphisms • Vii. Are several thousands of bases long

32. Viii. Once DNA is cut, it is sorted using electrophoresis • 1. fragments migrate across gel plate different distances depending on their length • 2. shorter fragments go farther, longer ones go less far

33. Ix. Once electrophoresis is complete, fragments are transferred to nylon sheet and treated with radioactively labeled probes containing complementary base sequences (this process is called hybridization) • X. Next nylon sheet is placed against x-ray film and exposed for several days

35. Xi. This test by itself is not enough to individualize DNA • Xii. Can use other probes to search for different repeating segments of DNA to get higher degree of differentiation or even individualization

38. Xiii. First technique accepted to characterize DNA • Xiv. New technology making this process more or less obsolete

39. b. Polymerase Chain reaction (PCR) • i. More viable method • Ii. Increased sensitivity • Iii. Can yield information from degraded samples • Iv. First, heat DNA to about degrees C, strands begin to separate

40. V. Second, add primers to separated strands and lower temp, so will hybridize • Vi. Primers = short DNA segments in pure form • Viii. Third, add DNA polymerase and free nucleotides, rebuilds double strands

41. Viii. Each cycle doubles the amount of DNA present • Ix. Usually go through 25-30 cycles • X. First validated PCR-based genetic marker system available for forensic science was DQA1 • 1. DQA1 gene has lots of variants

42. Xi. DNA is extracted from sample • Xii. Primer, DNA polymerase and nucleotides added • Xiii. Amplification process • Xiv. DNA is added to select areas of nylon strip • 1. nylon strips pre-affixed with probes • 2. blue dots will appear if DNA type is present

43. Xv. Generally, not a discriminating technique • Xvi. Polymarker (PM) = frequency of occurrence in range of 1/5000 • Xvii. Advantage of PCR = can use very small amounts of DNA (ex. saliva residues on stamps, cigarette butts)

44. c. Short Tandem Repeats • i. Latest method • Ii. Most successful and widely used • Iii. Used to identify bodies of victims of TWA Flight 800, Branch Davidian compound and September 11, 2001 • Iv. Higher discrimination than RFLP • V. Can use small sample size

46. Vi. STRs are locations on chromosome that contain in short sequence elements that repeat themselves within DNA molecule • Vii. Are useful because are found in abundance in human genome • Viii. STR is extracted and amplified • Ix. Are separated on electrophoretic gel

47. X. By examining the distance the STR migrated on the gel, one can determine the number of repeats that exist in the STR • Xi. Are hundreds of types of STRs • Xii. The more you can characterize the smaller the % of the population from which they can emanate

49. Xiii. Multiplexing – a technique that simultaneously detects more than one DNA marker in a single analysis • Xiv. Can determine sex of DNA contributor • Xv. Use amelogenin gene on X and Y chromosome

50. X. Mitochondrial DNA • A. Human cells have DNA in nucleus and mitochondria • B. mDNA is inherited solely from mother • C. Cells have hundreds of thousands of mitochondria, so better chance of extracting DNA • D. More sensitive than nuclear profiling • E. More time consuming and costly