DNA- A Molecular Identity (Research)
Evan Hardy
1) Define what DNA is and describe its function in general terms.
DNA is a double stranded nucleic acid that’s has the genetic information for division, cell
growth, and function.
Structure- DNA is made up of two strands that twist together and form a double helix. Each
strand has an alternating phosphate and deoxyribose sugars. On those sugars, there are
nitrogenous bases. Nitrogenous bases have four bases- Adenine, Thymine, Guanine, and
Cytosine. These four bases are out into pairs. Adenine pairs with Thymine, and Guanine pairs
with Cytosine.
Function- DNA is a long polymer of nucleotides to code for the sequence of amino acid
during protein synthesis. DNA is called a blueprint because it has all the instructions needed to
make components like proteins and RNA molecules.
2) Compare two different DNA typing techniques.
SNP- Single Nucleotide Polymorphisms or SNPs are differences in a DNA sequence that occur
when a single nucleotide in the sequence is different from the norm in at least one percent of
the population. Unlike repeated parts of DNA like STRs and VNTRs, in the case of SNPs it is the
sequence itself. SNP analysis is rarely used in forensic cases.
STR- A Short Tandem Repeat (STR) is a region of DNA composed of a short sequence of
nucleotides repeated many times. STR’s are short; this is because they are dispersed more
evenly throughout the genome. STRs are favored by forensic labs.
3) Describe different uses of DNA typing.
Personal Identification, Paternity and Maternity tests, Diagnosis and Cures for Inherited
Diseases, Criminal Identification and Forensics.
4) Identify possible benefits and misuses of DNA typing.
Advantages: DNA profiling is a great method for confirming an identity with absolute
certainty. It’s easy and painless to get a specimen for testing. A thorough, scientific test can be
made in as little as 48 hours. DNA testing is affordable and reliable.
Disadvantages: Misuse of results can lead to privacy concerns. There aren't that many labs
that can produce accurate results.
Vocabulary:
Allele- Any of several forms of a gene, usually arising through mutation, and are responsible for
heredity variation.
DNA- (Deoxyribose) an extremely long macromolecule that is the main component of
chromosomes and is the material that transfers genetic characteristics in all life forms.
Electrophoresis- The motion of colloidal particles suspended in a fluid medium, due to the
influence of an electrical field on the medium.
Gene- The basic physical unit of heredity, and a linear sequence of nucleotides along a segment
of DNA that provides the coded instructions for synthesis of RNA.
Mitochondrion- An organelle in the cytoplasm of cells that functions in energy production.
MtDNA- DNA found in the mitochondrion, which contains some structural genes and is
generally inherited only through the female line.
Nucleotide- Any group of molecules that, when linked together, form the building blocks of
DNA or RNA.
PCR-(Polymerase Chain Reaction) A way to make copies of a small amount of DNA by exploiting
DNA’s natural ability to replicate itself when a cell divides.
RFLP-(Restriction Fragment Length Polymorphism) Analysis measures fragments of DNA
containing short sequences that vary from person to person called VNTR’s.
STR-(A Short Tandem Repeat) A region of DNA composed of a short sequence of nucleotides
repeated many times.
SNP-(Single Nucleotide Polymorphisms) Variations in a DNA sequence that occur when a single
nucleotide in the sequence is different from the norm in at least one percent of the population.
VNTR-(Variable Number of Tandem Repeats) This can be isolated from an individual’s DNA.
Part 1:
1) VNTR Analysis- These stretches of repeats, known as Variable Number of Tandem Repeats
or VNTRs can be isolated from an individual’s DNA. The number of repeats can be gauged by
dividing the entire molecular weight of a given VNTR by the molecular weight of the repeated
sequence.
2) RFLP Analysis- analysis measures fragments of DNA containing short sequences that vary
from person to person, called VNTRs. The resulting fragments can be sorted by length with gel
electrophoresis technology to determine how many times a given VNTR is repeated. RFLP
testing requires hundreds of steps and weeks to complete, and it has been largely replaced by
newer, faster techniques.
3) SNP- Single Nucleotide Polymorphisms or SNPs are differences in a DNA sequence that
occur when a single nucleotide in the sequence is different from the norm in at least one
percent of the population. Unlike repeated parts of DNA like STRs and VNTRs, in the case of
SNPs it is the sequence itself. SNP analysis is rarely used in forensic cases.
4) STR- A Short Tandem Repeat (STR) is a region of DNA composed of a short sequence of
nucleotides repeated many times. STR’s are short; this is because they are dispersed more
evenly throughout the genome. STRs are favored by forensic labs.
5) PCR- A simple yet essential way to make copies of a small amount of DNA by exploiting
DNA’s natural ability to replicate itself when a cell divides. This sequence is repeated billions of
times in just a few hours, supplying ample DNA for investigation.
6) MtDNA- Most DNA is packed tightly into the cell’s nucleus; there is also a tiny loop of
genetic material, called mitochondrial DNA. Because of its relative abundance in the cell,
mtDNA can often be extracted from old or degraded samples in which nuclear DNA is sparse.
2) Evaluate whether one analysis may work better than another in a specific situation.
MtDNA would work better for old skeletal remains because; MtDNA can often be extracted
from old or degraded samples in which nuclear DNA is sparse. If the skeletal remains don’t have
much DNA left on them, then mtDNA would work well for this. Other analysis would have a
difficult time getting DNA from the old bones.
Part 2:
1. Explore three cases where DNA analysis was used in carrying out justice.
Case #1: On April 27, 1990, a woman in her fifties came home and was attacked by a man. The
man placed a pillow over her head and sexually assaulted her. In October 1990 Gilbert
Alejandro was convicted of aggravated sexual assault by a Uvalde County jury. He was
sentenced to 12 years in prison. Fred Zain, the chief forensic expert for Bexar County, Texas,
testified that a DNA test of Alejandro’s sample matched DNA found on the victim’s clothing
“and could only have originated from him [Alejandro].”
Case #2: On December 16, 1984, a nurse was grabbed from behind and sexually assaulted. On
July 25, 1985, Harris was arrested and charged with first-degree sexual assault. On October 18,
1987, Harris was sentenced to 10 to 20 years in prison. On May 1, 1995, a report from Dr. David
Bing of the Center for Blood Research Laboratories stated that DNA extracted from Harris’s
blood sample was consistent with DNA extracted from the semen on the evidence slide.
Case #3: On October 28, 1985, a woman was raped and sodomized in her apartment by a man
who had broken through her front door. Walter Snyder was convicted of rape, sodomy, and
burglary by an Alexandria, Virginia jury on June 25, 1986. The jury recommended a sentence of
45 years, which the judge accepted and ordered Snyder to serve. On October 28, 1992, CBR
issued a report stating that Snyder’s DNA did match the DNA in semen found on a vaginal swab
from the original rape kit.
Evaluation: Students can identify different situations where DNA analysis is used in modern
society and consider its ethical uses.
DNA analysis is used a lot these days. It can be used to identify a criminal in a murder
case, or a paternity test. DNA analysis is a huge help to our society.
Extension: Research and write about any positive and/or negative consequences of establishing
an international DNA database.
Positive consequences could be that people can get very accurate statements about a
criminal case or correct answers to a paternity test.
Negative consequences could be that some people would not their DNA to be held
inside a lab. Some people could steal their DNA and do very harmful or bad things with the
DNA.