Question

Allopatric speciation occurs when
A. Genetically related populations inhabit widely separated geographical area
B. Genetically unrelated populations inhabit widely separated geographical area
C. Genetically related populations inhabit the same geographical area
D. Genetically unrelated populations inhabit the same geographical area

Answer 1

Hint: The living organisms are always subjected to ever changing environmental conditions. The environment affects the organism by producing several factors which may or may not be suitable for the organism. On the other hand, the organism also incorporates certain changes to survive in the altered conditions by altering or addition of certain adaptations.

Complete answer:
In an ecosystem, the organisms live together in the form of populations. A population is defined as a group of organisms belonging to the same species residing in a particular geographical area. The populations are eligible for interbreeding. The populations are subjected to the various changing environmental conditions. In due course of time, several evolutionary processes act on the organisms of the population.

The different types of evolutionary forces bring about certain changes in the population and the changes are inheritable in nature. With time, the changes are incorporated and divide the species into new and distinct species. The different species formed are the derivative of a common ancestor but due to the different conditions have certain characteristics leading to the separation of their gene pool. The separation in their gene pool leads to the diversification of the population and this process is referred to as speciation.

The most common and widespread reason of speciation is through geographical isolation. In this process, the common population is isolated through geographical isolation and it prevents exchange of gametes and finally it leads to reproductive isolation. In some cases, the population is isolated and completely separated due to the presence of physical barriers such as mountains, rivers and deserts. This condition prevents the population from interbreeding with each other and the species are separated into two separate groups. The newly formed species are related to each other as they have the same ancestor. The species formed adopt their own habitats and environment which are different from one another.

Hence, the correct answer is option (A).

Note: The process of formation of new species from the same parental population due to presence of some types of physical barriers are known as allopatric speciation. In this type of process, the interbreeding and exchange of gene pool between the two species does not occur and each one develops adaptation according to its specific environment.