Genetic comparisons can be made between different species by direct examination of their DNA or of the proteins encoded by this DNA.

Genetic comparisons are made to find out the classification of a living thing, i.e. what its ancestors are.

Comparing DNA will show what characteristics two species have in common, and what mutations have been made to make them different.

This can also be done by looking at proteins because DNA codes for amino acids which make up proteins. Therefore looking at one protein from two species and seeing the similarities and differences in amino acids equates to seeing similarities and differences in their genetics.