Gene transfer to bacteria often involves small circles of DNA into which genes can be inserted. State the name of a small circle of DNA, used for DNA transfer, in bacteria.

The diagram below shows a cut circle of DNA into which a gene is being inserted. Before it can be transfered into a bacterium, the ring must be altered, using an enzyme.

Outline what must be done next to complete the process of gene insertion into the DNA circle, including the name of the enzyme that is used.

Discuss the potential benefit and possible harm of one named example of gene transfer between species.

plasmid

DNA ligase involved; (DNA required to be consistent with syllabus)
seals gaps/nicks in DNA (strands);
makes sugar-phosphate bonds;

named example of DNA source and organism to which it is transferred;
benefit of the example of gene transfer;
possible harm from the example of gene transfer;

Example:
gene transfer details [1 max]
e.g. Bt gene transferred from bacterium/Bacillus to maize
specific benefit [1 max]
e.g. corn borer/insect pest killed by Bt toxin increasing crop production;
e.g. less pesticides/fertilizers/chemicals needed so better for environment;
specific harmful effect [1 max]
e.g. non-target insects may be killed as well;
e.g. risk of cross-pollination may introduce gene to unintended species;

Examiners may have to consult resources for legitimate alternative examples.

Many candidates identified DNA circle as a plasmid, although some called it mRNA or used names of enzymes.

Ligase was frequently given but very few used the term DNA ligase, as seen in Assessment Statement 4.4.8 of the IB biology guide.  Very few spoke of sealing nicks or gaps, or mentioned joining sugar phosphate bonds. It was not realized that the sticky ends were already joined i.e. complementary base pairing had already occurred.  

This question was answered poorly. Actual examples (not hypothetical or unsuccessful) of gene transfer were required. Transfer details such as source of gene and transgenic species were rarely mentioned.  Sometimes, the cited potential benefit and possible harm of the gene transfer did not relate to the example provided.   

Gene transfer was also confused with cloning, cross-breeding, IVF, gene mutation or even bone marrow transplant. Some candidates gave only very general answers that gained no marks.  Others left the answer space entirely blank.