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Forensic Science > Blood and Semen Identification, and DNA > Flashcards

Blood and Semen Identification, and DNA Flashcards

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1
Q

What are two other terms for a presumptive test?

A
  1. PRELIMINARY
  2. SCREENING
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2
Q

What does it mean for a scientific test to be “presumptive”?

A

IT CAN ONLY “INDICATE” THAT THE BODY FLUID MAY BE PRESENT; IT DOESN’T PROVE CONCLUSIVELY
THAT IT IS PRESENT.

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3
Q

What are the two fractions of blood?

A
  1. FORMED ELEMENTS
  2. PLASMA
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4
Q

What does it mean for a scientific test to be “confirmatory”?

A

THIS TYPE OF TEST PROVES THAT THE BODY FLUID IS PRESENT SUCH AS “HUMAN BLOOD IDENTIFIED”

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5
Q

Define the function of the following blood components and state their function: Red blood cells:

A

GAS EXCHANGE; PICK UP OXYGEN AT THE LUNGS AND CARRY IT TO TISSUES; PICK UP
CARBON DIOXIDE IN TISSUES AND CARRY IT TO THE LUNGS

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6
Q

Define the function of the following blood components and state their function: White blood cells:

A

FIGHT INFECTION

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7
Q

Define the function of the following blood components and state their function: Platelets:

A

ESSENTIAL IN BLOOD CLOTTING

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8
Q

Define the function of the following blood components and state their function: Plasma:

A

KNOWN AS THE LIQUID PORTION OF BLOOD. CARRIES EVERYTHING ELSE THAT IS NOT A
FORMED ELEMENT SUCH AS VITAMINS, ELECTROLYTES, HORMONES, ANTIBODIES, ENZYMES, ETC.

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9
Q

What is the main presumptive test for blood and what color does it turn if positive?

A

KM; TURNS PINK

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10
Q

The main protein in blood is ____ which is comprised by 4 iron containing _____ groups.

A

-HEMOGLOBIN
-HEME

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11
Q

The two reagents needed to perform the KM test are:

A
  1. HYDROGEN PEROXIDE
  2. KM REAGENT
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12
Q

List four advantages of the KM test:

A
  1. SENSITIVE; NEEDS VERY SMALL SAMPLE TO PERFORM
  2. SAMPLE CAN STILL BE USED FOR DNA
  3. COST EFFECTIVE
  4. REAGENTS ARE STABLE AND NON-TOXIC
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13
Q

List three disadvantages of the KM test:

A
  1. CROSS REACTS WITH RUST, HORSERADISH, ROOT VEGETABLES
  2. CAN ONLY SAY THAT BLOOD IS “INDICATED”
  3. DOES NOT IDENTIFY SPECIES
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14
Q

Define the following:
Luminol:

A

HIGHLY SENSITIVE PRESUMPTIVE TEST FOR BLOOD; FLUORESCES WHEN SEEN UNDER
UV LIGHT

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15
Q

Define the following:
Hemastix:

A

PRESUMPTIVE TEST FOR BLOOD; STICK TURNS GREEN IF POSITIVE

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16
Q

How does the Ochterlony Double Diffusion Test work?

A

THE ODD TEST IS A PRECIPITIN TEST WHERE AN ANTIGEN (PROTEIN) WILL REACT WITH AN ANTIBODY
TO PRODUCE A SOLID PRECIPITATE. WELLS ARE CUT INTO A GEL AND CRIME SCENE SAMPLES
(ANTIGENS) CAN BE TESTED AGAINST VARIOUS ANTIBODIES.

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17
Q

Why is the ODD test especially useful in veterinary forensic cases?

A

THE ODD TEST CAN BE USED TO DETERMINE THE SPECIES (SUCH AS HUMAN, DOG, CAT, ETC) OF THE
SAMPLE

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18
Q

Is the ODD test presumptive or confirmatory?

A

CONFIRMATORY

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19
Q

What is the “ALS” and how it is useful in identifying possible semen stains on items of physical evidence?

A

ALS stands for “Alternate Light Source”. It is useful because semen will fluoresce under the ALS.

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20
Q

Where is the MAJORITY of the DNA located in a sperm cell?

A

The head of the sperm cell (which contains all the nuclear DNA from the father)

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21
Q

What other body fluid will fluoresce under the ALS?

A

Urine

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22
Q

What is the acrosome on a sperm cell and what function does it serve?

A

The acrosome is located on the tip of the head of the sperm cell. It contains a cluster of enzymes which
helps the sperm digest the through the thick layers of the egg so the sperm can enter the egg and
fertilization can occur.

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23
Q

True or False: Mitochondrial DNA from the sperm cell does NOT enter the egg when fertilization occurs:

A

TRUE

24
Q

True or False: You can have semen WITHOUT sperm, but you CANNOT have sperm without semen.

A

TRUE

25
Q

What is the main presumptive test to indicate that semen may be present on an item of evidence and
what color is produced if the test is positive?

A

The main presumptive test to identify semen is to screen for the presence of Seminal Acid Phosphatase.
If positive for the presence of semen, the SAP test will turn purple.

26
Q

What are the two confirmatory tests for semen?

A
  1. KPIC
  2. AbaCard (which tests for the p30 protein)
27
Q

List two advantages of using the AbaCard to test for the p30 protein to identify semen.

A
  1. It’s very sensitive (can identify semen even if diluted one million times). Therefore, there can be low
    amounts of semen and the test can still identify that amount.
  2. Because the p30 protein should only be found in semen, the test is very specific. And it can identify
    semen in males with a low sperm count or males who have been vasectomized
28
Q

What does DNA stand for?

A

Deoxyribonucleic acid

29
Q

What is the “double helix”?

A

The double helix refers to the shape of the DNA molecule; it looks like a ladder that has been twisted

30
Q

What are the two locations where DNA is found in your cells?

A
  1. the nucleus (which contains the majority of your DNA)
  2. the mitochondria (which contains a small amount of DNA from your MOM only)
31
Q

What is the only type of DNA found in your red blood cells?

A

Only mitochondrial DNA is found in your red blood cells because red blood cells do NOT have a nucleus but they DO have mitochondria.

32
Q

What percentage of DNA is the same between people?

A

99% of DNA is the same between people; we have the same GENES (like genes for
eye color, hair color, our liver enzymes, etc) but we can have different ALLELES in
these genes (example: we all have the gene for eye color, but the color can differ like blue, brown, green, etc)

33
Q

What are the two base pairing rules of DNA?

A
  1. A always pairs with T
  2. C always pairs with G
34
Q

What is a gene?

A

A GENE is a linear sequence of DNA (meaning the As, Gs, Cs and Ts) that carries the code to allow a single functional protein be produced.

35
Q

What percentage of your DNA contains genes?

A

Only 1% of your DNA contains actual, functional genes (though more and more
genes are being identified through research every day).

36
Q

What is “junk DNA”?

A

Junk DNA refers to any part of your DNA that DOESN’T contain genes.

37
Q

Why are forensic DNA locations found in “junk DNA” and not in functional genes?

A

This has to do with mutation. Mutation just means “genetic change over time”. When actual genes mutate, it can have a bad outcome and result in diseases like cancer. But the DNA where forensic sequences are found are NOT in genes. So, this means that they can “mutate” but nothing bad (like cancer) happens. The mutations that occur in forensic sequences just allow us to be able to tell people apart.

38
Q

What are STRs?

A

STR stands for “Short Tandem Repeats”. STRs are short sequences that are 3-7 base pairs in length that are then repeated side by side (tandemly) like boxcars on a train. The number of STRs (or boxcars) gives us the person’s DNA type.

39
Q

What gender is someone with the genetic type XX?

A

Female

40
Q

What gender is someone with the genetic type XY?

A

Male

41
Q

How many chromosomes does a human have?

A

46 total (23 are from your mom’s egg and 23 are from your dad’s sperm)

42
Q

How many genetic loci (locations) are tested in STR testing?

A

13 locations plus a marker called Amelogenin which tells us the gender of the sample (male XY or female XX)

43
Q

Why can the probabilities from the different genetic locations be multiplied together in STR testing?

A

Because each genetic location is considered an “independent event”. (You can review this topic in the Physical Evidence PowerPoint under probability). Genetic locations are specifically selected on SEPARATE CHROMOSOMES. The forensic
DNA profile on one chromosome has NO impact on the forensic DNA profile on a different chromosome. So, for example, your forensic DNA type on chromosome #5 has NO EFFECT on what your forensic DNA profile is on chromosome #6. So as
long as we look at forensic locations on differently numbered chromosomes, all the probabilities are considered independent and we can multiply them together to come up with the incredibly small probabilities that you hear about on criminal cases where there is a genetic match. For example, in my experience at the crime lab, it was very common for me to testify to something like: “The male DNA profile identified on the sexual assault evidence matches the DNA profile of the defendant. This DNA profile would be expected to occur in 1 in 9 billion Black, 1 in 3 trillion White or 1 in 2 quadrillion Hispanic individuals”. Since the population of the world is around 7.6 billion, what I’m basically saying is “this DNA profile is found in only one person on earth and it matches the defendant.”

44
Q

For what types of samples is traditional DNA extraction used?

A

Any sample that DOESN’T contain semen such as bloodstains, saliva, urine or any other type of non-semen body fluid.

45
Q

When is differential extraction used?

A

On any stain where semen is identified.

46
Q

The older type of DNA profiling used in the 1980s and 1990s is _____.

A

RFLP analysis

47
Q

What does PCR stand for and what is the purpose of this technique?

A

PCR stands for Polymerase Chain Reaction. PCR is a technique that works like a molecule xerox machine. It allows us to make millions of copies (from a single copy) of the specific forensic DNA locations we are interested in. We use PCR so that we will have enough copies of the forensic DNA sequences recovered from the body fluids on an item of evidence to be detected by the instrument we use (called CE which stands for capillary electrophoresis).

48
Q

DNA profiles are detected by using what technique?

A

CE which stands for capillary electrophoresis

49
Q

What are 5 case types where mitochondrial DNA would be used? ** basically any case where the bodies are damaged or decomposed to the point where the DNA from the nucleus has degraded.

A
  1. severely decomposed bodies
  2. badly burned bodies
  3. any event where bodies are very fragmented (such as an explosion)
  4. any event where bodies are decomposed and comingled (mass graves; natural disaster like Hurricane Katrina or the Asian Tsunami)
  5. any event where there are lots of bodies comingled, fragmented and
    decomposed (example-the collapse of the World Trade Center on 9/11)
50
Q

Why is mitochondrial DNA inherited only from your mother?

A

The egg (ovum) from your mom is a huge cell that contains a nucleus and lots of mitochondria. The sperm cell from your dad is much smaller (because it has to travel such a huge distance to reach the egg). Only the head of the sperm cell (which contains your dad’s nuclear DNA) makes it into the egg when fertilization happens. The sperm cell DOES have mitochondrial DNA, but it is located in the midpiece of the sperm cell and does NOT enter the egg. So, all of your mitochondrial DNA comes from your mom only.

51
Q

What percentage of violent crimes are committed by men?

A

99%

52
Q

What is “preferential amplification”?

A

Preferential amplification refers to being able to only pick up the DNA profile that is present in very large amounts compared to other DNA profiles present. For example, consider a large pool of blood that came from a victim bleeding out
from a wound. Let’s say the offender cuts him or herself and drops a single drop of their blood into the large pool. Likely the only DNA profile that will be detected will be the victim’s because the offender’s DNA (though it is there) is present in such a small amount compared to the victim’s.

53
Q

What are three case types where Y-STRs could be useful? (I gave you 5)

A
  1. A rape case where there is very little male DNA compared to the amount of female DNA
  2. A gang rape situation where there are multiple male DNA profiles present
  3. Rape cases (or cold cases) where the amount of male DNA present is very small
  4. Fingernail scrapings from a female rape victim
  5. From the ligature mark of a victim of strangulation
54
Q

What is CODIS and what is its purpose?

A

CODIS stands for the “Combined DNA Indexing System”. It is a computer system that allows law enforcement to store and compare DNA profiles from criminal cases, convicted offenders and unidentified remains. It allows DNA profiles to
constantly be searched against each other to generate investigative leads that would likely never be found using just “traditional” detective work such as connecting cases to each other or connecting a previously convicted offender to
an unsolved crime.

55
Q

What are the three levels of CODIS?

A
  1. LDIS (Local DNA Indexing System)
  2. SDIS (State DNA Indexing System)

3.NDIS (National DNA Indexing System)

56
Q

What serial killer inspired the development of CODIS?

A

Ted Bundy

57
Q

What is the difference between a CODIS “warm hit” and a “cold hit”?

A

A “warm” hit is when the investigating agency (such as a detective working on a homicide case) EXPECTS the hit. For example, during their investigation, they believe two rape/homicides are connected and the DNA hit just confirms their suspicions that it’s the same offender committing both crimes. A “cold” hit is one that is totally unexpected. An example would be a rape/homicide where the detectives don’t have any suspects. The DNA from the case would be put into CODIS and it produces a “hit” either to another unsolved case OR to the DNA profile of a convicted offender. This last one is the absolute BEST type of hit because it solves the crime!

Forensic Science (9 decks)

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