The poison warfarin was once the most popular form of rat control. Eventually warfarin-resistant rat populations emerged so people stopped using warfarin for rat control. Since then, the frequency of warfarin-resistant rats has once again declined. What may be the reason for this?
What will be an ideal response?
Since warfarin is not used as a form of rat control, there is no selective pressure to make the warfarin-resistant allele adaptive any more. The allele likely made the rats less healthy than rats without the mutation in the enzyme that recycles vitamin K. Therefore, the allele was now a harmful mutation once resistance to warfarin was not needed.
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Water moves (select all correct choices):
A. from regions of high water concentration to regions of low water concentration. B. from regions of low water concentration to regions of high water concentration. C. from regions of high solute concentration to regions of low solute concentration. D. from regions of low solute concentration to regions of high solute concentration. E. from regions of low water concentration to regions of low solute concentration.
Which of the following statements correctly traces the route of water through a sponge?
A. enters through the osculum into the spongocoel and exits via the ostia B. enters through the spongocoel into the osculum and exits via the ostia C. enters through the ostia into the osculum and exits via the spongocoel D. enters through the ostia into the spongocoel and exits via the osculum E. enters through the osculum into the ostia and exits via the spongocoel
In an antibody- mediated immune response, what causes effector helper T cells to release cytokines?
a. binding to antigen presenting dendritic cells
b. binding to a bacterial complement c. binding to a naive helper T cell d. binding to a B cell e. engulfing a bacterium
he route a pathogen uses to get into the human host is called the _____ of _____
Fill in the blank(s) with the appropriate word(s).