Unit 6

Question 1

Forensic Serology

Answer 1

The study of bodily fluids applied to crime.

Question 2

What can blood evidence do?

Answer 2

Connect an object with a crime. (bloody knife)
Connect a suspect with a crime. (victim’s blood stains on a suspect’s clothing or a suspect’s blood found at a crime scene)

Question 3

What is blood evidence?

Answer 3

Blood evidence is class evidence, except if it is used for DNA profiling and then it is individual evidence.

Question 4

Blood composition: plasma

Answer 4

Yellowish liquid; contains water and proteins, nutrients and wastes.
Makes up 55% of blood.

Question 5

Blood composition: platlets

Answer 5

Cells that assist in blood clotting.

Question 6

Blood composition: white blood cells.

Answer 6

Cells that fight infections; contain DNA. Makes up 4% of blood.

Question 7

Blood composition: red blood cells

Answer 7

Cells that carry oxygen and carbon dioxide, contains hemoglobin. Makes up 41% of blood.

Question 8

How is blood identified?

Answer 8

To identify blood, we use presumptive tests. These will tell us that there is definitely no blood, or that there is probably blood, nut it could be something else, so further testing must be done.

Question 9

When can presumptive tests be done?

Answer 9

When there is an easily visible stain (a red spot on a piece of fabric), or when a crime has occurred and we are looking for blood that we cannot see. (the blood has been cleaned up)

Question 10

Luminar test.

Answer 10

Ingredients react with the iron in the hemoglobin in the red blood cells.

Th products of the reaction can be visible with UV light.

Produces false positive results with bleach and some metals.

Question 11

Kastle-Meyer test.

Answer 11

Hydrogen peroxide reacts with the iron in the hemoglobin in the red blood cells.

The products of the reaction can be made visible with an indicator called Phenolphthalein.

Produces false positive results with potatoes and horseradish.

Question 12

How can we determine whether blood is Human or animal.

Answer 12

We can look at the blood under a microscope. The shape of the red blood cells is circular in mammals and oval in non-mammals. The nucleus is large and visible in non-mammals. See diagram on page 3

Question 13

Precipitin Test

Answer 13

Identifies the presence of proteins that are only found in human blood.

Rabbit blood is injected not the sample. If the sample reacts with rabbit blood, it is human blood. If the sample doesn’t react to the rabbit blood, it is animal blood. See diagram on page 3.

Question 14

What is blood typing used for?

Answer 14

Blood typing is often used to eliminate suspects. It is cheaper and faster than DNA profiling so it is often the first test done on a sample once it has been identified as blood. There are 4 blood types.

Question 15

What type of evidence is blood typing?

Answer 15

It is considered class evidence because it can help narrow the suspect field, but cannot directly link to a single person.

Question 16

What are blood types?

Answer 16

Blood types were discovered in 1900 by Kurt Landsteiner. Each blood type differs by the presence or abundance of antigens (proteins) in our red blood cells. blood also contains antibodies of the antigens in our red blood cells. Red blood cells also have an antigen called the RH factor. This gives a + or - associated with a A, B, AB, and O blood types, meaning that there are 8 different blood types. See diagram on page 4 and 5.

Question 17

Blood typing test.

Answer 17

Antigens and antibodies react with each other. Antibodies for A, B and Rh are added to a sample of blood. If a reaction occurs, the blood has the antigen for the antibody added. If nothing happens, it does not have the antigen. See diagram on page 5 and 6.

Question 18

Blood transfusions.

Answer 18

Blood types must be matched for a safe transfusion. Blood transfusions can occur between blood types that would not have a reaction so you can receive blood from any type that does not have the antigens for the antibodies in your blood. O- is the universal donor and AB+ is the universal recipient. See diagram on page 6.

Question 19

How is DNA used in Forensics?

Answer 19

No 2 people have the same DNA, except for identical twins. DNA in considered individual evidence because it can be linked to a specific person.

Question 20

Where can DNA be collected from?

Answer 20

Hair (with follicle), skin, blood, saliva, semen, and urine.

Question 21

DNA structure

Answer 21

DNA aka Deoxyribonucleic acid, is located in the chromosomes inside the nucleus of the cell. Humans have 46 total chromosomes (23 from Mother and 23 from Father). DNA can be broken down into genes that control traits. See diagram on page 7.

Question 22

What makes up DNA?

Answer 22

DNA is made up of many nucleotides, which have 3 parts. A nitrogen base, a phosphate group and a sugar. See picture on page 7.

Question 23

Why is DNA shaped like a double helix.

Answer 23

Because there are 2 strands that are connected by 4 nitrogen bases, adenine, thymine, cydozene, and guanine. See diagram on page 8. The nitrogen bases are always paired in the same way, A-T and C-G.

Question 24

Why is each pair of nitrogen bases considered complimentary?

Answer 24

Because one strand of DNA has the genetic code that is complementary to the other stand of DNA. Most of the human genome is the same in all humans. It’s what makes us human and not another species. However, there are variations that exist among individuals found in the non-coding portion of DNA. See page 8 diagram.

Question 25

DNA profiling

Answer 25

Also known as DNA fingerprinting.

It is a technique used by scientists to distinguish between individuals using samples of their DNA.

The process was developed by Sir Alec Jefferys in 1985.

It is helpful for identifying victims or suspects of crimes, establishing parentage, identifying victims of war or large disasters, settling immigration disputes, and diagnosis of diseases.

Within the non-coding portion of DNA, are areas made up of short tandem repeats (STRs), which are used to identify sequences that are unique to an individual. See image on page 9.

Question 26

Gel Electrophoresis

Answer 26

Gel electrophoresis is a technique which is used to separate fragments of DNA according to size.

Used to compare people’s DNA profiles.

Question 27

Steps of Gel Electrophoresis

Answer 27

1: Extract the DNA from the sample.
2: Add restriction enzymes to cut the DNA into fragments.
3: Add the DNA fragments to a gel and apply an electric current to separate the pieces by size. The small pieces will move more on the gel, while the large pieces move less.
4: The results are analyzed by forensic investigators.

See pictures on page 10.

Question 28

DNA profile databases

Answer 28

Each state keeps DNA profiles of individuals who have been convicted of certain crimes.

The military keeps DNA profiles of all service men and women.

The FBI keeps a national database of DNA profiles called CODIS (combined DNA index system). There are over 14 million profiles in the database. CODIS has aided in over 520,000 cases.

If DNA is not a match from these databases, a suspect sample is needed or comparison.