Rats are a major pest in many areas of the world. They can reduce food security and spread diseases.
Warfarin is a chemical that is used as a rat poison. It stops platelets working in the blood.
Describe the function of platelets in the blood.
Some rats are resistant to warfarin. When fed with large amounts of warfarin the rats do not die.
Scientists found that the resistance is due to the dominant allele R.
Two resistant rats (Rr) mate.
Complete this genetic diagram to find the ratio of resistant rats to non-resistant rats that would be expected to be produced.
Rr | |||
............ | ............ | ||
Rr | R | ............ | ............ |
r | ............ | ............ |
Ratio = ..................................
After several years, the percentage of resistant rats in the population had increased.
Use Darwin’s theory of natural selection to explain this observation.
Scientists are now trying to find another poison to use on rats.
They have introduced a chemical called phosphine. This blocks the action of mitochondria in rat cells.
Explain why this might kill rats.
When scientists studied the resistant rats they found that there were two different types.
Homozygous rats are resistant to warfarin but need to eat 20 times more vitamin K.
Heterozygous rats are resistant to warfarin but only need slightly increased amounts of vitamin K.
The scientists found that the non-resistant rats never died out completely.
Explain why.
Higher Tier only
Scientists now think that they might be able to reduce rat populations by using genetic engineering. They want to insert a gene into male rats that destroys all sperm that contain an X chromosome.
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You may use a diagram in your answer.
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