CBSE Class 10 Answered

Geographical isolation occurs when a portion of a species becomes totally isolated from the rest of the gene pool by some geographic changes such as formation of a mountain range, river valley, desert or ocean.

In order for geographic isolation to lead to speciation, the following steps are necessary:

• Geographic isolation of a sub-population of a species
• Genetic divergence of the isolated sub-population from the rest of the species
• Reproductive isolation of the new species from its parent species

For example, within populations of Hibiscus plant, some plants may breed or flower at a somewhat different time of the year. If the difference in reproductive time is genetically based, different breeding populations could be established, which could eventually lead to speciation.

Also, genetically determined incompatibility of the pollen of one population of flowering plants with the flowers of other populations of the same species could lead to the formation of new species.