Question

In a hypothetical situation, the Vermont State Park Service decides to build a pedestrian bridge over the Rock River in the town of Newfane. Upon completion, the pedestrian bridge will enable the passage of two closely related populations of mud lizards that had previously existed either on the eastern or the western side of the river but had been unable to cross the river.
Just before completion of the bridge and then fifteen years after the completion of the bridge, graduate students from the University of Vermont collected twenty-five lizards from each side of the river, took blood samples, and determined the frequencies of alleles that were unique to the two types of mud lizards. The results of their sampling are shown in the graphs below.
The data from the students' investigation show which of the following?

A. The completion of the bridge allowed for the formation of a hybrid zone between the Eastern and western mud lizards.
B. The eastern and western mud lizards did not intermix despite the construction of the bridge.
C. Gene flow occurred from the Eastern mud lizard gene pool into the Western mud lizard pool.
D. The two mud lizard populations intermixed after the completion of the bridge, but they did not hybridize.

Answer 1

Hybridization is the process of formation of a hybrid. It is any of mixed origin or the combination of two or more different beings. So, it refers to the process of producing offspring by mating two parents from different species. In animals, ligers (Tiger and Lion) and mules Horse and Donkey) are examples of a hybrid.

Complete answer:
Based on the above diagram we conclude that there was no hybrid mud lizard zone formed even after 15 years of bridge construction. The reason for intermixing is because of the gene flow from eastern mud into western mud lizard pool and western mud into eastern mud.
Gene flow is a process in which genetic variation is transferred from one population to another. It is a part of population genetics. It can take place between the two populations belonging to the same species. It is also considered as gene migration or gene flow.

The above assumption is based on Hardy Weinberg equilibrium and certain major assumptions include-
• Random mating
• No natural selection
• No mutation
• No migration
• Large population size.
Thus, the correct answer is that the two mud lizard populations intermixed after the completion of the bridge, but they did not hybridize.

Hence, the correct answer is option (D).

Note: Some important points-
• The completion of the bridge did not allow for the formation of a hybrid zone between the Eastern and western mud lizards as hybridization is an uncommon process in animals in nature and it commonly takes place in polyploidy species.
• Hybridization in animals is often termed as line crossing and strain crossing.