Multiple Choice
In forensic DNA analysis, which part of a hair is most likely to contain nuclear DNA suitable for STR profiling?
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18. Molecular Genetic Tools
Methods for Analyzing DNA
Multiple Choice
In agarose gel electrophoresis, the separation (analysis) of DNA fragments is primarily based on which property?
A
The net positive charge of DNA fragments causing them to migrate toward the cathode
B
Fragment size (length in base pairs), because DNA has a relatively uniform charge-to-mass ratio
C
The sequence of nucleotides determining unique colorimetric reactions in the gel
D
Base composition (percentage of content) independent of fragment length
Verified step by step guidance1
Understand the principle of agarose gel electrophoresis: DNA fragments are separated by applying an electric field to a gel matrix, causing the fragments to migrate through the gel.
Recall that DNA molecules have a uniform negative charge due to their phosphate backbone, which means their charge-to-mass ratio is relatively constant across different fragments.
Recognize that because the charge-to-mass ratio is uniform, the migration speed of DNA fragments in the gel depends mainly on their size (length in base pairs), with smaller fragments moving faster through the gel pores.
Note that the direction of migration is toward the positive electrode (anode) because DNA is negatively charged, so the statement about migration toward the cathode (negative electrode) is incorrect.
Conclude that the primary property used for separation in agarose gel electrophoresis is the fragment size (length), not the nucleotide sequence, base composition, or colorimetric reactions.
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