A day without electrophoresis is very rare in molecular biology labs, because this technique is the standard method used for analyzing, identifying and purifying fragments of DNA. It is also used for separating and analyzing RNAs and oligonucleotides.
Electrophoretic "gels" are composed of either agarose or polyacrylamide. These two substrates differ in resolving power, and also in the difficulty of setting them up - agarose gels are used much more commonly except for small fragments of DNA. Polyacrylamide gels are also widely used for electrophoresis of proteins.
Core concepts related to electrophoresis of nucleic acids:
Advanced and supplemental topics: