• Definition of Genetic Polymorphism (E. B. Ford / Cavalli-Sforza):
• In genetics and population genetics, a gene or DNA marker locus is formally defined as polymorphic if the frequency of the most common allele is less than $0.99$, meaning that at least one alternative variant allele occurs at a frequency of $\gt 1\%$ (or $\gt 0.01$) in the population.
• Variations occurring at frequencies $\lt 1\%$ are classified as rare spontaneous mutations rather than stable polymorphisms maintained by balanced selection or neutral drift.
• nalysis:
• (A variation of a gene or marker sequence present in >1% of the population): Correct.

Correct option: (4) A variation of a gene or marker sequence present in >1% of the population