Portions of the DNA structure are as unique to each individual as __________
Fingerprints
The __________ is the fundamental unit of heredity
Gene
Each gene is actually composed of DNA specifically designed to carry the task of controlling the __________ __________ of our cells
Genetic traits
DNA is constructed as a very large molecule made by linking a series of repeating units called __________
Nucleotides
A nucleotide is composed of a __________, a phosphorous-containing group, and a nitrogen-containing molecule called a __________
Sugar, base
Four types of bases are associated with the DNA structure: __________, __________, __________, and __________
Adenine, guanine, cytosine, thymine
The bases on each strand are properly aligned in a __________ __________ configuration, which is two strands of DNA coiled together
Double helix
As a result, adenine pairs with __________ and guanine pairs with __________. This concept is known as __________ __________
Thymine, cytosine, base pairing
The order of the bases is what distinguishes different __________ __________
DNA strands
DNA directs the production of __________, which are made by combining amino acids
Proteins
The sequence of __________ __________ in a protein chain determines the shape and function of the protein
Amino acids
Each group of __________ nucleotides in a DNA sequence codes for a particular amino acid
3
G-A-G codes for the amino acid __________ while C-G-T codes for __________
Glutamine, alanine
If a nucleotide is "changed," the "wrong" amino acid is placed in the protein. As a result, the protein may not function correctly, and this is the basis for many __________ and __________ __________
Diseases, health issues
DNA replicates itself prior to __________ __________
Cell division
DNA replication begins with the __________ of the DNA strands of the double helix
Unwinding
Each strand is now exposed to a collection of __________ __________ that will be used to recreate the double helix, letter by letter, using base pairing
Free nucleotides
Many enzymes and proteins, such as __________ __________, are involved in unwinding the DNA, keeping the DNA strands apart, and assembling the new DNA strands
DNA polymerases
__________ __________ __________ is a technique for replicating small quantities of DNA or broken pieces of DNA found at a crime scene, outside a living cell
Polymerase chain reaction
The ability to multiply small bits of DNA now means that __________ __________ is no longer a limitation in characterizing DNA recovered at a crime scene
Sample size
__________ __________ relies on the ability of certain chemicals, known as restriction enzymes, to cut DNA into fragments that can later be incorporated into another DNA strand
Recombinant DNA
__________ __________ can be thought of as highly specialized scissors that cut a DNA molecule when it recognizes a specific sequence of bases
Restriction enzymes
Once a portion of the DNA strand has been cut out with the aid of a restriction enzyme, the next step in the recombinant DNA process is to insert the isolated DNA segment into a foreign DNA strand, usually that of a __________
Bacterium
As the bacteria multiply rapidly, copies of the altered DNA are passed on to all __________
Descendants
Portions of the DNA molecule contain sequences of bases that are repeated numerous times, known as __________ __________
Tandem repeats
To a forensic scientist, these tandem repeats offer a means of distinguishing one individual from another through __________ __________
DNA typing
Tandem repeats seem to act as fillers or spacers between the __________ __________ of DNA
Coding regions
What is important to understand is that all humans have the __________ __________ of repeats, but there is tremendous variation in the number of repeats each of us have
Same type
Length differences associated with relatively long repeating DNA strands are called __________ __________ __________ __________ and form the basis for one of the first DNA typing procedures
Restriction fragment length polymorphisms
Typically a core sequence consists of __________ to __________ bases in length and repeats itself up to a thousand times
15, 35
The key to understanding DNA typing lies in the knowledge that __________ __________ exist for the number of times a particular sequence of base letters can relate itself on a DNA strand
Numerous possibilities
A technique analogous to thin-layer chromatography is __________. Here, materials are forced to move across a gel-coated plate under the influence of an electrical potential
Electrophoresis
In this manner, substances such as DNA can be __________ and __________
Separated, characterized
Once the DNA molecules have been cut up by a restriction enzyme, the resulting fragments are __________ __________ by electrophoresis
Sorted out
The smaller DNA fragments will move at a __________ rate on the gel plate than the larger ones
Faster
The fragments are then transferred to a nylon membrane in a process called __________ __________
Southern blotting
To visualize the RFLPs, the nylon sheet is treated with radioactive probes containing a base sequence complementary to the RFLPs being identified, a process called __________
Hybridization
Next, the nylon sheet is placed against __________ __________ and exposed for several days
X-ray film
When the film is processed, __________ appear where radioactive probes stuck to fragments on the nylon sheet
Bands
A typical DNA fragment will show __________ bands, one RFLP from each chromosome
2
When comparing the DNA fragment patterns of two or more specimens, one merely looks for a __________ between the band sets
Match
A high degree of __________ can be achieved by using a number of different probes and combining their frequencies
Discrimination
Polymerase chain reaction is the outgrowth of knowledge gained from an understanding of how DNA strands naturally replicate within a __________
Cell
For the forensic scientist, PCR offers a distinct advantage in that it can amplify __________ __________ of DNA many millions of times
Minute quantities
First, the DNA is heated to separate it. Second, __________, short strands of DNA used to target specific regions of DNA for replication, are added, which hybridize with the strands. Third, DNA polymerase and free nucleotides are added to rebuild each of
Primers
The process of PCR is repeated __________ to __________ times
25, 30
__________ __________ cannot be applied to RFLP DNA typing
PCR technology
The RFLP strands are __________ __________, often numbering in the thousands of bases
Too long
PCR is best used with DNA strands that are no longer than __________ bases
200
One advantage in moving to shorter DNA strands is that they would be expected to be more stable and less subject to __________ brought about by adverse environmental conditions
Degradation
The long RFLP strands tend to readily break apart under the __________ __________ not uncommon at crime scenes
Adverse conditions
PCR also offers the advantage in that it can amplify minute quantities of DNA, thus overcoming the limited sample size problem often associated with __________ __________ __________
Crime scene evidence
The latest method of DNA typing, __________ __________ __________ __________, has emerged as the most successful and widely used DNA profiling procedure
Short tandem repeats analysis
__________ __________ __________ are located on the chromosomes that contain short sequences that repeat themselves within the DNA molecule
Short tandem repeats
STRs serve as useful __________ for identification because they are found in great abundance throughout the __________ __________
Markers, human genome
STRs normally consist of repeating sequences of __________ to __________ bases in length, and the entire strand of an STR is also very short, less than __________ bases in length
3, 7, 450
This means that STRs are much __________ __________ to degradation and may often be recovered from bodies or stains that have been subjected to extreme decomposition
Less susceptible
Also, because of their shortness, STRs are __________ __________ for multiplication by PCR
Ideal candidates
What makes STRs so attractive to forensic scientists is that hundreds of __________ __________ of STRs are found in human genes
Different types
The more STRs one can characterize, the __________ will be the percentage of the population from which a particular combination of STRs can emanate. This gives rise to the concept of __________
Smaller, multiplexing
Using the technology of PCR, one can simultaneously extract and amplify a __________ of different STRs
Combination
Currently, the U.S. crime labs have standardized on __________ STRs for entry into the national database, Combined DNA Index System
13
A high degree of discrimination and even __________ can be attained by analyzing a combination of STRs, or multiplexing, and determining the product of their frequencies
Individualization
With STR, as little as __________ picograms (one trillionth of a gram) of DNA is required for analysis. This is __________ times less than that normally required for RFLP analysis
125, 100
Another type of DNA used for individual characterization is __________ __________
Mitochondrial DNA
Mitochondrial DNA is located outside the cell's __________ and is inherited from the __________
Nucleus, mother
__________ are strictures found in all our cells used to provide energy that our bodies need to function
Mitochondria
A single mitochondria contains several __________ of DNA
Loops
__________ __________ __________ does not approach STR analysis in its discrimination power and thus is best reserved for samples, such as hair, for which STR analysis may not be possible
Mitochondrial DNA typing
Forensic analysis of mDNA is __________ __________, time consuming, and costly when compared to nuclear DNA analysis
More rigorous
Also, all individuals of the same __________ __________ will be indistinguishable by mDNA analysis
Maternal lineage
Two regions of mDNA have been found to be highly variable and a procedure known as __________ is used to determine the order of base pairs
Sequencing
Perhaps the most significant tool to arise from DNA typing is the ability to compare DNA types recovered from crime scene evidence to those of convicted __________ __________ and other convicted criminals
Sex offenders
__________ __________ __________ __________ is a computer software program developed by the FBI that maintains local, state, and national databases of DNA profiles from convicted offenders, unsolved crime scene evidence, and profiles of missing persons
Combined DNA Index System
Before the collection of biological evidence begins, it is important that it be __________ and __________ on sketches
Photographed, recorded
Wearing disposable latex __________ while handing the evidence is required
Gloves
Clothing from victim and suspect with blood evidence must be __________
Collected
The __________ of biological evidence in plastic or airtight containers must be avoided because the accumulation of residual moisture could contribute to the growth of DNA-destroying bacteria and fungi
Packaging
Each stained article should be __________ __________ in a paper bag of in a well-ventilated box
Packaged separately
__________ __________ is best removed from a surface by using a sterile cotton swab lightly moistened with distilled water that is air dried before being placed in a swab box, then a paper or manila envelope
Dried blood
All biological evidence should be __________ or __________ in a cool location until delivery to the lab
Refrigerated, stored
__________ or __________ DNA specimens must also be collected, such as blood or the buccal swab (swabbing the mouth and cheek)
Standard, reference
__________ __________ is a forensic method for analyzing DNA left at the crime scene. It is called this because it only requires very small samples, for example from the skin cells left on an object after it has been touched or casually handled
Touch DNA
The first criminal case to involve DNA analysis in forensics was that of two murdered girls and performed by one of the people who developed DNA fingerprinting. The convicted person was __________ __________. This case was in __________
Colin Pitchfork, England
Colin Pitchfork is a British convicted murderer and rapist. He was the first person convicted of __________ based on DNA fingerprinting evidence, and the first to be caught as a result of mass DNA screening. Pitchfork raped and and murdered two girls in L
Murder