Final answer:
Mutation is the ultimate source of new genes and new cells in a species, allowing for the evolution of a species over time. Gene flow and sexual reproduction are also important sources of genetic diversity.
Step-by-step explanation:
The ultimate source of new genes and new cells in a species is mutation, which is a permanent change in DNA sequence. Mutation is what generates new genetic variation in a population and allows for the evolution of a species over time. Other sources of genetic diversity include gene flow, which is the flow of alleles in and out of a population due to migration, and sexual reproduction, which combines genetic material from two individuals to create new combinations of alleles.