Biology 9700 · AS & A Level · Principles of genetic technology

Principles of genetic technology — practice question

White-clawed crayfish, Austropotamobius pallipes, are found in rivers and lakes across Europe. In the 1850s, the North American signal crayfish, Pacifastacus leniusculus, was brought into Europe. The introduced species carried a pathogen that leads to a disease called crayfish plague. This disease kills A. pallipes. Since 1850, the population size of A. pallipes has fallen in many parts of Europe because crayfish plague has spread.
(a)[4]

North American P. leniusculus are able to carry the crayfish plague pathogen without showing symptoms because they have become resistant to it. Explain how P. leniusculus may have evolved resistance to the crayfish plague pathogen.

(b(i))[4]

Outline and explain the stages that take place in PCR.

(b(ii))[1]

Suggest how the researchers could identify suitable sequences for the primers.

(c(i))[1]

State the letter of the curve with the greatest starting concentration of DNA.

(c(ii))[1]

The amount of A. pallipes DNA reaches a threshold (shown as a horizontal line on Fig. 4.1) at 28 cycles. The DNA in curve C reaches the threshold after 25 cycles. In one cycle of PCR the concentration of DNA doubles. Calculate the fold difference between the starting concentrations of A. pallipes DNA and the DNA in curve C.

(d(i))[3]

Identify the component that normal bacteria take up to produce the genetically modified bacteria in Fig. 4.2, and state what it contains so the bacteria can make green fluorescent protein.

(d(ii))[1]

Suggest why the gene for green fluorescent protein is sometimes transferred in addition to the desired gene in genetic engineering.

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