Forensic biology

what is bloodtyping

a serological test that yields the phenotype of the sample by identifying blood group based on antigens and antibodies

How does bloodtyping work

  The lab technician will run an ABO typing test by mixing your blood with antibodies against type A and B blood. If your blood reacts and cells stick together, it indicates a match with one of the antibodies, determining your blood type.

Antibody and Antigen interaction

• Basis for serological identification; binding causes agglutination or precipitation

• process involves the formation of an antigen-antibody complex, which is then yransported to cellular systems where it can be destroyed or deactivated

Antibody definition:

proteins that are produced for the purpose of binding to and aiding in the elimination of non-self material

Antigen definition:

the material that an antibody binds to

Precipitin test (antibody profiling):

a precipitin test is when an antibody reacts with a soluble antigen to form a visible, insoluble precipitate

type A blood:

A antogen, anti-B antibody

type B blood

B antigen, anti-A antibody

type AB blood

A and B antigens, no antibodies

radioimmunoassay

• uses radiolabeled molecules for the formation of immune complexes and determines the concentration of antigens.

Enzyme-linked immunosorbent assay (ELISA)

technique that detects certain antibodies, antigens and other substances in bodily fluids using enzyme assay

Enzyme multiplied immunoassay technique (EMIT)

• faster than ELISA but less clean

• method that utilizes enzyme-labeled antibodies to detect specific substances in a sample.

Rh + and - factor

Rh⁺ has the D antigen; Rh⁻ lacks it.

Nuclear DNA

• Unique to individual; used in Combined DNA index system (CODIS), effective only if suspect’s profile is in database.

what is the Combined DNA Index System

databank of all criminal DNA analysis performed at all levels, maintained by the FBI

Mitochondrial DNA

• inherited from maternal line

• can address familial relationships, connections to ancestors, and prehistoric human migration

Y-chromosome DNA

• Only passed paternally; useful in male identification or sexual assault with mixed samples.

Limitations of DNA evidence

• Degraded/contaminated samples, partial profiles, database dependence, cannot always identify specific individual (esp. mtDNA, Y-DNA).