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Rat Poison


An allele in a rat population prevents proper Vitamin K metabolism. Rats with this trait are selected against and are found at a low frequency.

However, rats with this trait have resistance to Warfarin, a poison that works by causing fatal bleeding (Warfarin is also used medically in humans as an anticoagulant).

A public health office chooses to use Warfarin to reduce the city's rat population. Initially,​ the rat population decreases dramatically. After a few generations though, the rat population increases.

Genetic testing reveals that most of the rats are resistant to Warfarin, so they discontinue the use of the poison. After several years, genetic testing is performed again.

Which of the following are the expected results?


Few rats will be resistant to Warfarin because the resistant allele is no longer needed, so it will decrease over time.


Few rats will be resistant to Warfarin because without the poison, the resistant rats have a lower fitness than the nonresistant rats.


The frequency of the Warfarin resistance trait will continue to increase to prepare the population for future introduction of Warfarin to the environment.


The frequency of Warfarin resistance will remain the same. Without selection, the gene will be at equilibrium.