FRSC 1011H Lecture Notes - Lecture 15: Guanine, Antigen, Genetic Testing
7 May 2018
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Department
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Professor
Biological Stain Analysis: DNA
Blood Typing
● More than 15 blood antigen systems have been identified, but the A-B-O and Rh
systems are the most important
● An individual that is type A has A antigens on his/her red blood cells, type B has
B antigens, AB has both A and B antigens, and type O has neither A nor B
antigens
● Rh factors is determined by the presence of another antigen, the D antigen
● People having the D antigen are Ph positive; those not having the antigen are Ph
negative
● For every antigen there is a specific antibody that will react with it to form clumps
known as agglutination
● Thus, if serum containing anti-B is added to red blood cells carrying B antigens,
they will immediately react.
Forensics of Blood
● The forensic scientist must be prepared to answer the following questions when
examining dried blood
○ Is it blood?
○ From what species did the blood originate?
○ If the blood is of human origin, how closely can it be associated to a
particular individual?
● The determination of blood is best made by means of a preliminary color test
The Structure of DNA
● DNA is a very large molecule composed of linked repeating units called
nucleotides
● A nucleotide is composed of a sugar, a phosphorus containing group, and a
nitrogen-containing molecule called a base
● Four types of bases are associated with the DNA structure: adenine (A), guanine
(G), cytosine ( C), and thymine (T)
● The bases on each strand are properly aligned in a double-helix configuration,
which is two strands of DNA coiled together
● As a result, adenine pairs with thymine and guanine pairs with cytosine
● This concept is known as base pairing
Standardizing STR Testing
Document Summary
More than 15 blood antigen systems have been identified, but the a-b-o and rh systems are the most important. An individual that is type a has a antigens on his/her red blood cells, type b has. B antigens, ab has both a and b antigens, and type o has neither a nor b antigens. Rh factors is determined by the presence of another antigen, the d antigen. People having the d antigen are ph positive; those not having the antigen are ph negative. For every antigen there is a specific antibody that will react with it to form clumps known as agglutination. Thus, if serum containing anti-b is added to red blood cells carrying b antigens, they will immediately react. The forensic scientist must be prepared to answer the following questions when examining dried blood. The determination of blood is best made by means of a preliminary color test.
