<Ul> <Li> </Li> <Li> </Li> <Li> </Li> </Ul> <P> Genetic variation means that biological systems--individuals and populations--are different over space . Each gene pool includes various alleles of genes . The variation occurs both within and among populations, supported by individual carriers of the variant genes . </P> <P> Genetic variation is brought about, fundamentally, by mutation, which is a permanent change in the chemical structure of chromosomes . Genetic recombination also produces changes within alleles . </P> <P> Genetic variation among individuals within a population can be identified at a variety of levels . It is possible to identify genetic variation from observations of phenotypic variation in either quantitative traits (traits that vary continuously and are coded for by many genes (e.g., leg length in dogs)) or discrete traits (traits that fall into discrete categories and are coded for by one or a few genes (e.g., white, pink, red petal color in certain flowers)). </P>

Changes in the gene pool can occur due to various mechanisms