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DNA : The Indispensable Forensic Science Tool Chapter 9
SFS3f. Compare short tandem repeat patterns (STR) and relate to identifying the DNA of an individual.
SFS3g. Explain the use of the DNA database for DNA profiling.
Introduction
1.
What did Alec Jeffries and his colleagues discover at Leicester University in 1985 that was so important to the world of
forensic science?
2.
What is meant by “DNA fingerprinting?
What is DNA
3.
Define:
a. Chromosome-A threadlike structure in the cell nucleus composed of DNA, along which the genes are located.
b.
Gene-Fundamental unit of heredity
c.
Polymer-A substance composed of a large number of atoms; these atoms are usually arranged in repeating units or
monomers.
d.
Nucleotide-
e.
complementary base pairing-The specific pairing of base A with T and base C with G in a double stranded DNA
f.
nuclear DNA-DNA found in the nucleus of a cell
g.
mtDNA-DNA found outside the nucleus of the cell and is inherited solely by the mother.
h.
DNA profiling-The process of isolating and reading DNA markers
i.
Radioactive probe-A molecule labeled with a radioactive isotope, dye or enzyme, that is used to locate a
particular sequence or gene on a DNA molecule
j.
Nitrogeneous bases-The 4 types of bases associated with DNA
k.
Backbone of DNA
l.
Polymerase- any of several enzymes that catalyze the formation of a long-chain molecule by linking smaller
molecular units, as nucleotides with nucleic acids.
m. Restrictive enzymes- Chemical that acts as scissors to cut DNA molecules at specific locations.
n.
Southern blotting- The transfer of DNA to a nylon membrane to be visualized.
4.
Draw the complementary base pairs for:
ATAA
CATT
CAGT
TATT
GTAA
GTCA
5.
Explain the relationship of DNA and identical twins.
The DNA of identical twins is the same.
6.
The average human chromosome contains about __ 100 million _base pairs.
7.
In what type of biological evidence can DNA be found?
Blood-WBC
Saliva
Hair
Urine
Mucus
Tissue
Semen
Ear wax
Vaginal or rectal cells
8.
In what specific structure can DNA be found in? Chromosomes
DNA at Work
9.
What does DNA direct, or do? Controls our genetic traits. DNA directs the production of proteins, which are made by
combining amino acids
10. The building blocks of proteins are __aminoacids________ and the building blocks of DNA are __nucleotides__..
11. Each structure of DNA is made up of how many DNA strands? Describe the shape of a DNA structure.
Each DNA structure is made up of 2 strands that are arranged in a double helix
12. Explain how sickle cell hemoglobin differs from normal hemoglobin.
The 6th protein in sickle cell is Valine which is GTG and the protein should be Glutamate which is GAG
13. How many pairs of chromosomes are in a human cell? ____________23 pairs
14. Identify genotype for male and female.
Male-XY Female-XX
15. Draw the complementary base pairs for:
CGTAAACTACGT
GCATTTGATGCA
16. What is the human genome and what was accomplished in the “human genome” project?
The total amount of DNA in a cell, which is contained in chromosomes and mitochondria.
Replication of DNA
17. What are two jobs of DNA polymerases?
(1) Synthesize a specific region of DNA.
(2) Directs rebuilding of a double stranded DNA molecule, extending the primers by adding the appropriate bases, one at a
time, resulting in the production of two complete pairs of double-stranded DNA segments
18. What is the technique for replicating or copying a portion of a DNA strand outside of a living cell?
19. What is the purpose of gel electrophoresis? Sort and measure DNA Describe the steps of this process.
(1) Place DNA samples in holes at one end of gel
(2) Add electrical current to make DNA move through gel
(3) Short strands move through the gel quicker than the long strands. Over time the shorter strands in the sample will
move farther away from the starting point than the longer strands. DNA strands of the same length will move at the
same speed and end up grouped together. In this way, the DNA strands in the sample sort themselves.
(4) Staining the sorted DNA makes them visible to the naked eye. Although we cannot see a single strand of DNA, we can
see larger groups of stained DNA strands. These groups show up as bands in the gel.
Describe how fast different size fragments move. Short strands move through the gel quicker than the long strands.
Recombinant DNA: Cutting and Splicing DNA
20. What is meant by “recombinant DNA”?
Recombinant DNA (rDNA) molecules areDNA molecules formed by laboratory methods of genetic recombination (such as molecular
cloning) to bring together genetic material from multiple sources, creating sequences that would not otherwise be found in
biological organisms
21.
(1)
(2)
(3)
(4)
List the steps that molecular biologists use in fashioning a recombinant DNA strand.
A restrictive enzyme cuts the DNA molecules from two different sources.
When mixed together the two different DNA fragments are joined.
Insertion into host cell
Replication
pg 334
DNA Typing
22. List the steps of the DNA typing process.
(1) digestion with restriction enzyme
(2) electrophoresis
(3) Southern Blotting
(4) Hybridization with a radioactive probe
(5) process with X-Ray film
23. What are “tandem repeats” and why are they important to geneticists?
Regions of a chromosome that contains multiple copies of a core DNA sequence arranged in a repeating fashion.
24. What is the job of RFLP’s?
DNA typing-forensic characterization of DNA. Restrictive Fragment Length Polymorphisms are repeat segments cut out of DNA by a
restrictive enzyme that acts like a pair of scissors. The core sequence is typically 15- 35 bases long and repeats itself up to a 1000
times
25. How were RFLP’s used in the impeachment trial investigation of former President Bill Clinton?
Monica Lewinsky had a dress with semen on it from President Clinton. The FBI lab compared the DNA from the dress to that of Bill
Clinton. A seven probe RFLP match was obtained. Between the DNA from the dress and DNA from Bill Clinton. The combined
frequency of occurance for the seven DNA types found was nearly one in eight trillion.
Polymerase Chain Reaction
26. Describe the steps of performing PCR on a DNA segment.
Fill PCR tube with all of the reaction components.
*Move extracted DNA into PCR tube
*Add Primer(s) to PCR tube with DNA in it
*Add nucleotides to PCR tube
*Add DNA polymerase to PCR tube
Place PCR tube in DNA Thermal Cycler
*Thermal cycler heats up to 95oC…to separate strands of double helix
*Thermal cycler cools down to 50oC…Primers lock onto target on single DNA strands
*Thermal cycler changes temp to 72oC…this activates DNA polymerase. When DNA polymerase locates a primer attached to a single
DNA strand, it begins to add complementary nucleotides onto the strand.
Cycle 1 complete. This continues through 30 cycles to produce over a billion fragments that contain only your target sequence.
(1) Temp raised to separate DNA strands
(2) Temp lowered so primers will attach
(3) Temp raised slightly to stimulate DNA polymerase to copy strand
27. From a forensic scientists’ viewpoint, why is PCR so important, or what does PCR allow that would never have happened
from RFLP?
PCR is important because it can be used to duplicate strand of DNA a million of times in a short period of time. RFLP strands are too
long, often containing 1000’s of bases. PCR is best used with DNA strands that are no longer than a couple of hundred bases.
Shorter DNA strands are more stable and less subject to degradation.
Short Tandem Repeats
28. What are STR’s? (Short tandem repeats)
STR’s normally consist of repeating sequences of 3-7 bases; the entire strand of an STR is also very short, less than 450 bases
long.
29. Explain 3 advantages in using short tandem repeats for DNA analysis.
*Less susceptible to extreme decomposition
*Because of their shortness STR are ideal for multiplication by PCR; thus overcoming the limited sample size problem often
associated with crime scene evidence.
*Only 1 billionth of a gram or less of DNA is required
30. Currently in the US, the forensic science community has standardized on _13 Core STR Loci___ _____ for entry into a
national database known as __CODIS____.
Mitochondrial DNA
31. List pros and cons of using mitochondrial DNA for DNA testing.
Pros
Cons
Can be obtained from any maternally related relative
Shows only maternal linkage
More sensitive than nuclear DNA
Analysis is more rigorous and time consuming & costly
Can use mtDNA when nuclear is not available
32. How is mitochondrial DNA inherited? Maternal
33. List 3 differences between mtDNA and nuclear DNA.
mtDNA
Located in mitochondria of cells
Loop shape
Maternal linkage
100’s to 1000’s copies of mtDNA in a cell
Nuclear DNA
Located in nucleus of cells
Linear shape
Both parents contribute
1 set of nuclear DNA per cell
CODIS
34. What is CODIS and how is CODIS used by law enforcement ?
Combined DNA Index System. A computer software program developed by FBI that maintains local, state and national DNA profiles
from convicted offenders, unsolved crome scene evidence, arrestees, and missing people.
35. Who (agencies; states) has access to CODIS
All state law enforcement agencies and more than 25 countries
Extra stuff I forgot to include:
36. Who is credited with the discovery of the structure of DNA?
James Watson & Francis Crick
37. Illustrate the DNA structure with 4 nucleotides. Include all 4 bases in illustration. Pg 327 fig 9-2
38. What is the number of nitrogenous bases needed to code for a specific amino acid? __3__
39. In the investigation of The mystery of the Romanov’s, who claimed to be Anastasia Romanov? Was it ever proven that she
definitely was Anastatia?
It was proven through DNA anaylysis on tissue and hair of Anna that she was not Anastatia
40. Compare advantages of short DNA fragments to longer DNA fragments.
Shorter fragments do not degrade as quickly. Shorter fragments travel in gel electrophoresis quicker