Analyzing dna by gel electrophoresis allows researchers to
a. identify similarities and differences in the genomes of different kinds of organisms
b. determine whether a particular allele of a gene is dominant or recessive
c. compare the phenotypes of different organisms
d. cut dna with restriction enzymes

A. identify similarities and differences in the genomes of different kinds of organisms

Explanation:

DNA gel electrophoresis is a method often used in molecular biology, for the separation and analysis of DNA fragments.

Just like the name says it is performed on the gel (e.g. agarose gel) and electric field is applied for the separation of negatively charged DNA fragments. Fragments are separated by size (short fragments travel faster towards the positive electrode). Results of the gel electrophoresis are visualized via a DNA-binding dye and UV light and compared with standard reference called DNA ladder.