Allopatric speciation occurs by seperation of organisms by geographic isolation. Allopatric speciation may occur by migration. Since, the gene flow between organisms is inhibited, the geographically isolated organisms form into two separate species due to adaptations to new geographical environment. Allopatric speciation is most common type of speciation observed in various organisms. Speciation may occur in population inhabited in same geographical area but exhibit reproductive barriers. Such speciation is known sympatric speciation and it is rare and it may result in polyploidy. Solution Allopatric speciation occurs by seperation of organisms by geographic isolation. Allopatric speciation may occur by migration. Since, the gene flow between organisms is inhibited, the geographically isolated organisms form into two separate species due to adaptations to new geographical environment. Allopatric speciation is most common type of speciation observed in various organisms. Speciation may occur in population inhabited in same geographical area but exhibit reproductive barriers. Such speciation is known sympatric speciation and it is rare and it may result in polyploidy..