Final answer:
A DNA sequence variation present in less than 1% of the population is a mutation, while one present in more than 1% is a polymorphism.
Step-by-step explanation:
If variation in DNA sequence is present in less than 1% of the population, it is known as a mutation; but if it is present in more than 1% of the population, it is known as a polymorphism. A specific type of polymorphism, where variation in just one nucleotide in alleles is present, is called a single nucleotide polymorphism (SNP) if it occurs at frequencies greater than 1 percent in a population.
Understanding the frequency of certain alleles, such as those in SNPs, is crucial for studying genetic variance and tracking how it changes over time, which can contribute to genetic drift and the overall process of evolution. By comparing allele frequencies and observing changes, researchers can determine which genetic variations are likely to influence phenotypic traits, including susceptibility to diseases or reactions to medications. This is fundamental for FINDING DISEASE VARIANTS.