而一个种群则由经过基因（gene）编码的一定数目的个体(individual)组成。每个个体实际上是染色体(chromosome)带有特征的实体。染色体作为遗传物质的主要载体，即多个基因的集合，其内部表现（即基因型）是某种基因组合，它决定了个体的形状的外部表现，如黑头发的特征是由染色体中控制这一特征的某种基因组合决定的。(A population consists of a certain number of individuals encoded by a gene. Each individual is actually an entity with a chromosome. Chromosome as a major carrier of genetic material, that is, a collection of multiple genes, the internal performance (ie, genotype) is a combination of certain genes, which determine the external shape of the individual performance, such as the characteristics of black hair is controlled by the chromosome A combination of certain characteristics of a gene.)