Nucleotide diversity

Nucleotide diversity is a concept in molecular genetics which is used to measure the degree of polymorphism within a population.
One commonly used measure of nucleotide diversity was first introduced by Nei and Li in 1979. This measure is defined as the average number of nucleotide differences per site between two DNA sequences in all possible pairs in the sample population, and is denoted by formula_1.
It is given by the formula:
where formula_3 and formula_4 are the respective frequencies of the formula_5 th and formula_6 th sequences, formula_7 is the number of nucleotide differences per nucleotide site between the formula_5 th and formula_6 th sequences, and formula_10 is the number of sequences in the sample.
Nucleotide diversity is a measure of genetic variation. It is usually associated with other statistical measures of population diversity, and is similar to expected heterozygosity. This statistic may be used to monitor diversity within or between ecological populations, to examine the genetic variation in crops and related species, or to determine evolutionary relationships.
Nucleotide diversity can be calculated by examining the DNA sequences directly, or may be estimated from molecular marker data, such as Random Amplified Polymorphic DNA (RAPD) data and Amplified Fragment Length Polymorphism (AFLP) data.