Biology 9700 · AS & A Level · Passage of information from parents to offspring
Passage of information from parents to offspring — practice question
Resistance to the poison warfarin is now very widespread among rats. Warfarin blocks an enzyme in the liver, vitamin K epoxide reductase, which is needed to recycle vitamin K. This vitamin is used in making the substances needed for blood clotting.
Rats that are vulnerable to warfarin die from internal bleeding.
Rats that are homozygous for resistance to warfarin do not suffer internal bleeding when their diet supplies more than $70\,\mu\text{g}$ of vitamin K per kg body mass per day.
Heterozygous rats are resistant to warfarin when their diet supplies about $10\,\mu\text{g}$ of vitamin K per kg body mass per day.
(a)[3]
Using suitable symbols, complete the genetic diagram to show how two resistant rats can produce offspring that are susceptible to warfarin.
(b)[1]
Rats that are homozygous for warfarin resistance have a low survival rate in the wild. Suggest why this is so.
(c)[2]
Suggest, giving a reason, the type of inhibition warfarin has on the enzyme vitamin K epoxide reductase.
(d)[3]
The allele for warfarin resistance may have arisen by a single base substitution and produced a modified vitamin K epoxide reductase. Explain how a single base substitution may affect the phenotype of an organism.
Worked solution & mark scheme
This 9-mark question has a full step-by-step worked solution and mark scheme. One marking point: “Accurate genetic cross showing $W^R$ and $W^S$ alleles with resistant and susceptible offspring” …