LEQ: HOW DOES DNA PROFILING WORK? 12.8 to 12.12

NUCLEIC ACID PROBES  Short single strands of DNA w/ specific nucleotide sequences are created using radioactive isotope or dye  These probes are used to find a specific gene or nucleotide sequence – the probe hydrogen bonds to gene of interest

DNA MICROARRAY

DNA MICROARRAY TEST FOR GENE ACTIVITY  mRNA that produces protein of interest is isolated, reverse transcriptase & fluorescent nucleotides are added  cDNA is made from RNA  cDNA is applied to well that contain DNA from a cell; cDNA will bind to DNA that is complementary in the wells  Rinse unbound cDNA – fluorescent spots show DNA that is being expressed by the cell; no glow = unexpressed DNA  Enables a researcher to determine what genes are turned on or off in a cell

Gel Electrophoresis Negatively charged DNA is placed into the wells at the negative end of the gel; apply current; negative DNA is pulled to the positive end; smaller pieces travel farther faster; DNA fragments are separated based on the size of the fragment (# of base pairs).

RESTRICTION FRAGMENT LENGTH POLYMORPHISMS (RFLP’S)  (rif ′ -lips) The differences in homologous DNA sequences that are reflected in different lengths of restriction fragments produced when the DNA is cut up with restriction enzymes  Here you are looking at homologous chromosome segments – one from a crime scene and the other from the suspect; when you cut both with the same restriction enzyme, they produce different banding patterns – This tells you the crime scene DNA did not come from the suspect

RFLIP’s used to ID Harmful alleles Compare individual that has a disease/harmful allele to others. Digest DNA from all individuals using same restriction enzyme. Run gel electrophoresis. Blot DNA (pick up DNA using special filter paper). Apply radioactive probe designed to detect (bind to) harmful allele / gene of interest. Unattached probes are rinsed off. Photographic film used to form a image that compares individuals. In this picture I had the harmful allele. If any individual matches the banding pattern of I, then they also have the harmful allele. Individual II – has the harmful allele but III doesn’t.

DNA Fingerprinting A procedure that analyzes an individual’s unique collection of DNA restriction fragments, detected by electrophoresis and nucleic acid probes. DNA fingerprinting can be used to determine whether two samples of genetic material are from the same individual. Used to convict criminals, determine paternity, exonerate innocent individuals, etc…