Serology

The Bodily Fluids

Your identity shows up in more places than your driver’s license…

Sources of DNA

• Blood• Semen• Teeth• Skin• Hairs• Urine• Bones• Muscle

Blood, sweat, tears, semen, saliva, and vaginal fluids are some of the bodily

fluids that are frequently found at the scene of a

crime. Investigators can determine a

suspect’s or victim’s identity through

a science called Serology

So, let’s get the ‘short story’ fluids out of the way

first….Semen: fluoresces

(glows) when an ultraviolet light or laser light shines on a sample.

Sperm is only found in semen so finding them under a microscope is absolute proof that semen is present

Vaginal Fluids

Vaginal fluid is more difficult to detect than semen. Epithelial cells that line the vagina are high in glycogen (a starch which is stored within the cells).

Periodic Acid-Schiff (PAS) is a reagent that stains glycogen a bright magenta color in the presence of vaginal fluid.

The Glitches

Not all vaginal epithelial cells contain glycogen. Cells from young women who have not begun menstruating as well as cells from post-menopausal women rarely contain glycogen. Many times the test comes back negative even though vaginal fluids are present.

SalivaSaliva is another fluid commonly found at crime scenes. Saliva can be found from food, a cigarette butt, eating utensils, or even from an envelope of a threatening letter.

During sexual assaults semen, saliva and vaginal

fluid are commonly transferred to the victim, the victim’s clothing or

nearby surfaces.

Timing is everything…Finding out when sexual intercourse or rape occurred often is critical in forensics and courtroom procedures.

The duration of sperm mobility in living victims is from 4-6 hours. In the case of rape-homicide, sperm can remain in the vagina of the victim for up to two weeks.

Dried semen stains can remain identifiable and useable for DNA analysis for many years even after dry cleaning!

SecretorsApproximately 80% - 85% of the population are secretors meaning they emit proteins of their ABO blood type in all bodily fluid, including seminal fluid, saliva, and tears. ABO types found in these fluids can be used to eliminate a suspect in rape, but they cannot accurately identify the individual who secreted them.

This brings us to Blood

Blood by far is the most common bodily fluid left at a crime scene and it’s the most useful because it opens up many avenues of investigation for the forensics team to travel down.

Understanding Blood• Blood is a mixture of many components.• The liquid portion of blood is the

plasma. It contains proteins, enzymes, clotting factors, electrolytes and various cells.

• Serum is the yellowish liquid leftover after the blood clots.

• Blood cells come in three types:Leucocytes or white blood cells (WBC)Erythrocytes or red blood cells (RBC)Platelets or tiny cells involved in blood

clotting.

ABO blood grouping system

According to the ABO blood typing system there are four different kinds of blood types: A, B, AB or O (null).

Do you know what type you are???

Antigens – Antibodies

What makes you the type that you are? Blood group A

If you belong to the blood group A, you have A antigens on the surface of your red blood cells and B antibodies in your blood plasma.

Blood group B

If you belong to the blood group B, you have B antigens on the surface of your red blood cells and A antibodies in your blood plasma. 

???

What do you think blood type

AB looks like?

Type O?

Blood Type AB Blood Type O

What about this Rh stuff?

Think of the + and – of a blood type as another antigen found on the surface of a RBC. If you are positive (Ex: A+) you have the extra protein. If you are negative, you do not have the extra protein.

Fill in the chart with the appropriate terms:

Blood Group

AntigensAntibodie

sCan give blood to

Can receive blood from.

AB A & B NoneA, B, AB,

or O

A A B A or O

B B A B or O

O None A & B O

It can get more complicated…

% of US Population

OK…so what does this have to do with forensic science?

First, if you find blood at a crime scene you can eliminate someone from being a suspect with a quick blood typing test (DNA fingerprinting is so expensive and takes weeks to complete). It may not pinpoint someone specific but it is useful.

Who’s Your Daddy???

A Jerry Springer show in the making….

Remember Punnett squares from Biology???

(Cue: Say ‘yes’)

A women wants to find out if so-and-so is the father of her baby. She wants child support and is convinced that he is the true father.

She takes him on TV and wildly denies that she has been with many other guys; only ‘him’. The baby has blood type A. Mom has blood type AB and Dad has blood type ‘B’. Can he be the father?

Remember that the genotype for blood types can be either homozygous or heterozygous. So, what do you remember?

Mom’s genotype is definitely AB. Dad can be homozygous (BB) or he could be heterozygous (BO) for blood type B.

Place the genotypes in the Punnett and figure out the possible offspring of this union. Is ‘so-and-so’ the father? Is this conclusive?

A B

B

B

A B

B

O

Now we get to the crime scene itself…

We see that there has been a crime committed and that there appears to be red liquid in the area. We need to answer the questions:

1.Is this blood? 2.Is it human blood?3.Whose blood is it?

Tests to determine whether blood’s really blood

Kastle-Meyer Color Test: Phenolphthalein and Hydrogen Peroxide… Reacts with the heme group of hemoglobin and causes a dark pink color to appear.

Hemastix strip – A pretreated stick that when in contact with the heme group of blood will turn the strip blue-green.

Luminol – When sprayed on a questioned area will glow even if the area has been covered up or washed with bleach.

Is it human?

• How might we determine if blood is human or some other animal?

P.S. When collecting blood from a crime scene be sure to package the blood after it dries. Remember that wet evidence packaged will be rendered unusable if mold or bacteria start to grow. Blood is vulnerable to Putrefaction (decay).

What is all of that scientificy stuff regarding

DNA and blood?DNA fingerprinting, PCR, STR is the way to individualize samples. It is very incriminating. Don’t even bother to deny anything if DNA points to you… unless you are an identical twin!

In a very, very small nutshell….

There are two main techniques used for the analysis of DNA, restriction fragment length polymorphism (RFLP) and polymerase chain reaction (PCR). Each takes the most unique parts of DNA, creates banded patterns from those sections and compares them to others to seek similarities.

RFLP vs. PCR

• Both tests are expensive but PCR will be even more expensive

• RFLP can take up to 2 weeks while PCR can take up to a month to receive results

RFLP’s are great if you have a blood sample the size of a quarter but sometimes you don’t have that much. PCR is so sensitive that you can have as little as that which is the size of a head of a pin.

The printout of the RFLP looks like a bunch of

horizontal lines stacked up.

PCR readouts show alleles and whether the person is

homozygous or heterozygous for that gene. It’s really quite involved so just know that you will get

caught if you leave your DNA around.

Oh, and there is the ‘other’ kind of DNA…

• There is mitochondrial DNA which not the same as the DNA taken from the nucleus.

• Mitochondrial DNA is found in the mitochondria (the ‘powerhouses’) of the cell. Mitochondrial DNA is only handed down from the maternal side of the family. Identical copies from the mother are passed down to all of the offspring. This means that the mDNA is identical among brothers and sisters. You can really put a family together by comparing mDNA.

• It also means that mDNA is horrible at individualizing people but really great at establishing lineage.

• mDNA can stay preserved in bone cells so well that you can process mDNA from bones that are hundreds of years old.

• You can compare your mDNA to skeletons from the 1600s to see if they were related.

• Hopefully, your distant ancestors weren’t criminals. Your family inheritance may be in question.

CODISCODIS stands for Combined DNA Index System which is a database of DNA fingerprints taken from felons and from biological fluids obtained from crime scenes such as assaults, rapes and homicides. As of 2004, the Connecticut State Crime Lab has expanded its facilities and has taken responsibility for much of this National Data Bank.

Intro to Serology Homework Questions

1. Which 3 questions would you ask yourself if you think you see blood at a crime scene?

2. What are the 3 possible tests to see if it is blood?

3. Name one difference between RFLP and PCR.

4. What are the cons of using mDNA?5. What is CODIS?