GMID-X Data Analysis and Evaluation Flashcards
What sizing algorithm is commonly used in data analysis?
Local Southern Method
Describe the Local Southern Method?
The Local Southern Method utilizes 4 fragments in the ILS closest to the unknown fragment to determine the unknown fragment’s size. It does this by averaging two size curves: curve 1 uses 2 peaks before and 1 peak after, curve two uses 1 peak before and 2 peaks after.
What are primer peaks?
Primer peaks are the result of all the left-over primers from the amplification process crossing the detection cell first due to their small size. Primer peaks are present on the far left side of the egram and in high concentration compared to the allelic peaks.
The presence of primer peaks indicates what?
Amp product is present
The presence of orange size standard peaks indicates what?
CE master mix is present
Is minus (-) A a technological or biological artifact?
Biological
What is minus (-) A?
A biological artifact that is due to incomplete adenylation at amplification. -A is present at one base pair shorter than the true peak, resulting in a “split peak”.
Is migration a technological or biological artifact?
Technological
What is migration?
A slowing or speeding up of the DNA through the capillary due to the environment (i.e. temperature). Usually indicated as multiple OL’s in the right side of the egram.
What does the x axis represent on an egram? And what does that correlate to?
X axis = measure of time when the fragment was detected; which correlates to base pair size
What does the y axis represent on an egram? And what does that correlate to?
Y axis = intensity/height of the peak (RFUs); which correlates to amount of DNA present
What does it mean if a sample is degraded?
DNA is damaged and severed into many pieces. This can be caused by environmental conditions, improper storage, etc. Larger loci are prone to degradation due to longer sequences, this results in the egram exhibiting a downward “ski-slope” effect in peak heights.
What is a possible resolution if you have a degraded sample?
Re-amplify the sample with more template DNA to increase the peak heights at the larger loci.
What is a null allele?
When a true allele does not amplify, usually due to a primer binding site mutation.
What is an allelic ladder?
The allelic ladder is an artificial mixture of the most common alleles in the population and is used to assign allele calls in the evidence sample.