Question 2

Cavendish banana crops are affected by banana bacterial wilt (BBW), which is caused by a bacterial pathogen. There is no effective chemical control for this pathogen and no species of banana has immunity against this pathogen. A genetically modified strain of Cavendish bananas has now been produced by introducing a BBW resistance gene from green peppers. Rhizobium larrymoorei is a bacterium capable of transferring DNA into plants. The techniques/steps involved in splicing the BBW resistance gene from green peppers into a plasmid previously isolated from this bacterium is outlined below.

■Step 1: Addition of restriction enzyme EcoRI cuts the plasmid once in the lacZ gene.

■Step 2: The cut plasmid is mixed with a supply of BBW resistance genes with complementary sticky ends to the treated plasmid.

■Step 3: Ligase is added to the plasmid/ BBW resistance gene mixture.

■Step 4: The mixture is added to a population of untreated rhizobium bacteria. The lacZ gene produces a blue pigment when active (bacteria not containing the pigment will be white). The amp gene, when active, provides resistance against the antibiotic ampicillin.

In step 2 when the plasmids and BBW resistance genes are mixed together and some plasmids incorporate the BBW gene. a. Why is it important to use the same restriction enzyme on both the BBW gene and the plasmid? b. What name is given to a plasmid which has incorporated a gene from a different source, such as the BBW gene from green peppers? In step 4 the plasmids were incubated with the rhizohium bacteria. A small number of bacteria took up a plasmid. Of those bacteria that took up a plasmid, some took up a plasmid that includedthe BBW gene.the BB c. Explain how the researcher was able to distinguish between bacteria that had taken up a plasmid, and those that had not. d. Explain how the researcher was able to distinguish between bacteria that had taken up a plasmid containing the BBW resistance gene, and those that had taken up a plasmid without the BBW resistance gene. e. Identify one social and one biological issue raised by the use of the GM bananas. f. Distinguish between the terms genetically modified organisms and transgenic organisms.