Final answer:
The sequence of nucleotides in DNA chains primarily produces diversity among individuals and species.
Step-by-step explanation:
The primary factor that produces diversity among individuals and species is the sequence of nucleotides in DNA chains. DNA contains the genetic instructions for the structure and function of cells and organisms, and the arrangement of nucleotides in genes determines the inheritable characteristics of all organisms. Genetic diversity arises from random mutations, which result in variations in the genetic code and serve as the basis of natural selection during evolution.