DNA PROFILING Flashcards
What does STR stand for
Short Tandem Repeats
What are polymorphic sequences
many form sequences
Locus
a unique location where STR’s are on a chromosome
STRs are difficult to replicate T or F
True
T or F an individual locus
can have many variants called alleles that differ in the number of tandem repeats contained in
the sequence. The difference in tandem repeat number makes some alleles longer than others.
True
What is electrophoresis?
“carry with current”.
What is multiplex PCR?
It uses more efficicency.
Porous gels are made from solidified agarose, a
complex carbohydrate made from seaweed. What is it used for?
They form a molecular mesh. It is submerged in a special chamber with electrodes.
What is a DNA allele ladder?
A reference standard that allows all of the possible alleles
What is genotyping?
Explain the power of discrimination
, the power of discrimination is the ability of the profile to discriminate
between different individuals. The larger the number of loci typed, the more powerful the
ability to discriminate.
Explain Locus frequency
formula locus
frequency = 2pq . True or False. If the two alleles are the same, like 6-6 then locus frequency= p2
. Using suspect A
as an example we would calculate a locus frequency of 2 x 0.23 x 0.11 = 0.051. T
True
Name the common locuses for forensic matching and examination
Explain RMP (random match probability)
Since our profile
used two genotypes we get to multiply the locus frequencies together to create a Random
Match Probability (RMP).
In our example the RMP equals the TH01
frequency (.051) multiplied by the D13S820 locus frequency (0.0064). The product is 0.00032 or
1 in every 3100 people. Do you understand this?
If not, try more.
Our forensic specialist uses 13 loci to increase the power of
discrimination to 1/53 quintillion (that’s 53 followed by 18 zeros). It is a little overkill but it does
ensure that even if an individual has all of the most common alleles for each locus their profile
will still be unique and when you deal with people’s lives you want to be as sure as possible. Does this make sense to you?
IF not, read more.
What are allele frequencies?
: the distribution of an allele in the general population. These are measured in the general
population by the National Institute of Standards and Technology. Allele frequencies are different for different
populations. Allele frequencies are represented by the letters p and q. (It doesn’t matter which is which but it is
common to label the frequency for the smaller allele p and the frequency for the larger allele q)
What are locus frequencies?
: The probability that two alleles will occur in a single genotype. Genotype is the allele
combination in an individual. The Locus Frequency is calculated using the equation 2pq if the alleles are different
or p
2
if the alleles are the same.
how to calculate Random Match Probability (RMP).
The probability that two multi-loci profiles
will match due to chance. It is calculated by multiplying the Locus frequency for each locus used in the profile.
The smaller the number the better
What precautions do detectives use when collecting evidence?
- Always wear gloves. Skin is an excellent source of cells containing DNA, and everyone sheds skin cells
constantly. Only a few cells are needed as the basis for DNA profiling. Gloves can help prevent
contamination of suspect collection. - Tie hair back or cover it. As we’ve already mentioned, a single hair is all it takes to implicate someone at a
particular place. - Sneezing or coughing can expel cells all over evidence, so a mask is often worn.
- Crime scenes, and evidentiary samples, must be treated in such a way that biological materials are not
accidentally transferred from one place to another, thereby providing misleading associations. In one
famous crime scene, the body of the victim was covered with a blanket from the household – this mistake
made any hairs found on the victim of no value since it wasn’t possible to determine whether they were
evidence of contact with the person who committed the crime, or were simply transferred to the victim by
accident.
What is contamination when it comes to evidence?
It means the sample is not pure and has been tampered with.
What does CODIS stand for and what is it?
Combined DNA index system
What is PROP 69 in California?
