Migrations

Date: 2015-10-07; view: 396.

Selection acts on individuals, not their individual genes. Sexual reproduction increases variation by reshuffling the genetic information from parents into new combinations in their offspring. Mutations produce new alleles. Mutations is a materiel for activity of natural selection.

Gene mutations result in new alleles, and are the source of variation within populations. Gene mutations are ultimately behind the other mechanisms that provide variation. Due to DNA replication and DNA repair mechanisms, mutation rates of individual genes are low, but since each organism has many genes, and a population has many individuals, new mutations arise in populations all the time. Thus, mutations are relatively common, and the mutation rate is an adequate source of new alleles. High levels of molecular variation are common in natural populations, although many mutations (usually recessive) are hidden.

Mutations

The mutation rate varies greatly among species and even among genes of an individual. Mutations are caused by errors in DNA replication, chemicals, or radiation. Large scale effects of mutation result only when mutation is combined with other factors that reshuffle the gene pool.

Gene flow moves alleles among populations through interbreeding as well as by migration of breeding individuals. Gene flow increases variation within a population by introducing new alleles produced in another population. Continued gene flow tends to decrease the diversity among populations, causing gene pools to become similar. Reduction or restriction of gene flow between populations is essential for the development of new species.