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.
What are the expected results?