topic 6 - infection, immunity, and forensics Flashcards
(14 cards)
what are the 4 fingerprint patterns?
arch, tented arch, whorl, and loop
what are the 3 methods of making fresh fingerprints visible?
- using aluminium, iron, or carbon powders that stick to the print
- using superglue, which reacts with the water and other substances left by the print
- using ninhydrin, which reacts with the amino acids in sweat
if an individual has no fingerprints on record, what may be another method of identifying them?
dental records (or DNA profiling)
what is an intron?
non-coding blocks of genes - intragenic region
what is an exon?
any genes within the coding region - expressed region
what is an STR?
short tandem repeat - sequences of repeated bases within introns - can contain from 2 to 50 base pairs and can be repeated 5 to several hundred times
how does the presence of STRs assist DNA profiling/
the same STRs occur at the same locus on both chromosomes of a homologous pairs, however the number of times they are repeated on each can be different. each person has a large number of introns with lots of STR loci. there is a large amount o variation in the number of repeats at each locus. two individuals are highly unlikely to have the same combination of STRs
how is a DNA profile made?
- tissue sample must be obtained
- sufficient DNA must be extracted to manipulate in the laboratory
- fragments of different lengths are created by cutting up DNA
- fragments are separated and visualised
- profile created is compared with another
how can a DNA sample be obtained?
cheek swab cells, white blood cells found in blood at crime scene, bone marrow in a skeleton, sperm cells
how is DNA obtained from a sample?
the tissue sample is physically broken down in a buffer solution that includes salt and a detergent to disrupt the cell membranes. the small suspended particles, including the DNA, are separated from the rest of the cell debris by filtering or centrifuging. protease enzymes are incubated with the suspension to remove proteins and then cold ethanol is added to precipitate out the DNA
how are DNA fragments created?
restriction enzymes are found naturally in bacteria, where their function is to cut up viral DNA. these enzymes will only it DNA at specific base sequences. if the same restriction enzyme is used to cut two identical DNA samples, identical STR fragments are produced
how are DNA samples copied?
PCR (polymerase chain reaction)
what is the polymerase chain reaction?
DNA primers (short DNA sequences complementary to the DNA adjacent to the STR) are marked with fluorescent tags. the forensic sample is placed in a reaction tube with DNA polymerase, DNA primers, and nucleotides. once in the PCR machine, the tube undergoes a cycle of temperature changes. the first separates the double stranded DNA, and the second optimises binding of the primer to the target DNA sequence. then, the polymerase attaches and replication occurs.
this continues, and huge numbers of the targeted DNA fragments are produced
how are DNA fragments separated after PCR?
- DNA is placed on a gel of agarose or polyacrylamide, to provide a stable medium
- the gel is submerged in a buffer solution, and connected to electrodes that produce a potential difference across the gel
- negatively charged DNA fragment migrate through the gel according to their overall charge and size
- smaller fragments travel faster an further
