Serology Unit Review

Question: What blood type does a person with A and B antigens but no Rh antigens present on their RBC’s surfaces have? Answer: Blood type AB-

Question: What is the blood type of a person that has both A & B antibodies in their plasma? Answer: Blood type O+

Question: What does the point of convergence of lines drawn through several bloodstains tell an investigator? Answer: The point from which the blood originated

Question: Can you identify a suspect based on his blood type alone matching that found at a crime scene? Answer: Absolutely not! Millions if not billions of people have similar blood types. Anyone with a similar blood type to the suspect could be found equally guilty of that evidence alone.

Question: What is the difference between a presumptive and a conclusive test? Answer: A presumptive test is a preliminary test that does not give official results. A conclusive test gives you accurate and official results.

Question: What does the Kastle-Meyer test do? Answer: It is a presumptive test used to determine if a blood sample is present.

Question: What is the probability of a child being born with the blood type “O” when the mother has a genotype AO and the father has a genotype AA? Answer: There is no chance that these two parents can have a child with an “O” blood type. 100% of their children will have the blood type “A.” Remember that in order to have a phenotype of “O” the genotype must be OO.

Question: What does a positive result look like for the Kastle-Meyer test? Answer: A positive result is pink. The oxygen in the hemoglobin reacts with phenolphthalein to produce the pink color.

Question: What package should be used for the collection of blood evidence? Explain. Answer: Paper bags should be used for collection of all biological material including blood. Paper bags allow the sample to “breathe” and thus preventing growth and contamination of bacteria and mold.

Question: List all three questions that the criminalist must be prepared to answer when examining dried blood. Answer: (1) Is it blood? (2) Is it human blood? (3) From which human did the blood originate?

Question: The precipitin test is used to answer the question “Is it human blood?” Draw a diagram of a positive result for the capillary tube precipitin test. Answer:

Question: When a drop of blood falls on a mildly absorbent surface, such as a piece of computer paper, from a 90 degree angle, what do you expect the shape of the blood spatter to be? Answer: A circle

Question: From what direction did this blood spatter originate? Answer: From the left

Question: What happens to the shape of a blood spatter as the angle of impact is decreased? Answer: The shape of the blood spatter becomes elongated (longer length, shorter diameter, longer tail)

Question: What is the clumping together of RBC by the action of an antibody? Answer: Agglutination

Question: Explain why it is important to consider the surface texture when interpreting a blood spatter? Answer: In general, the harder and less porous the surface, the less spatter results. Correlations between standards and unknowns are only valid if identical surfaces are used.

Question: What is the study of antigen-antibody interactions? Answer: Serology

Question: What one article of clothing is crucial to obtain from a male suspect involved in a rape case? (Assuming you have a suspect in a minimal amount of time). Answer: You want to collect the suspect’s undergarments as they may have traces of the female victim’s DNA present from intercourse.

Question: How can we link a blood or semen sample to an individual suspect with confidence? Answer: Through DNA testing

Question: What is the term for a blood-soaked item traveling over a non-blood soaked surface? Answer: A swipe is when a blood-soaked item travels over a non-blood-soaked surface.

Question: As the height increases from where a blood spatter is dropped, the diameter _____ unitl _____ cm height. Answer: The diameter increases up to cm based on the surface texture present.

Question: What is the luminol test used for? Answer: Luminol is a reagent that when in the presence of blood fluoresces. This helps CSI’s answer the question “Is it blood?”

Question: What is the role of a restriction enzyme? Answer: To cut the DNA into smaller fragments

Question: HAE III recognizes GGCC. What is GGCC? Answer: A restriction site.

Question: What is the color of DNA? Answer: It is clear.

Question: True/False. Identical twins have the same DNA and fingerprints. Answer: False. They have identical DNA but individual fingerprints.

Question: Put the following steps in order to create a DNA fingerprint. A. Hybridization of probes B. Gel electrophoresis C. DNA extraction D. Application of restriction enzymes Answer: C, D, B, A

Question: What was the role of adding detergent to the strawberry mixture in the DNA extraction lab? Answer: To break open the cell membrane that is a phospholipid bi-layer. Detergent cuts fats/lipids.

Question: You are attempting to figure out the angle of impact of a blood spatter. You measure the width of the spatter and find it to be 0.55cm. You measure the length of the spatter and find it to be 1.00cm. What is the calculated angle of impact? Answer: 34 degrees angle of impact.

Question: You measure a blood spatter at the scene to be 1.4cm in diameter. At what height did this spatter originate? Answer: 50 cm