Describe karyotyping and one application of its use.

Describe a technique used for gene transfer.

Using a named example, discuss the benefits and harmful effects of genetic modification.

cells undergoing mitosis are used for karyotyping;

process of mitosis is stopped at (mitotic) metaphase;

chromosomes (cut from photographs) are arranged in pairs of similar structure/ homologous chromosomes;

allows abnormalities in the chromosome number/appearance to be seen;

any valid example (e.g. in Down syndrome / gender of fetus);

detected by identifying unique feature (e.g. trisomy 21 / one extra chromosome / 47 chromosomes);

Award [3 max] for an example with no description of karyotyping.

restriction enzymes/endonucleases cut a small fragment of DNA from an organism;

same restriction enzymes used to cut DNA of plasmid / e.g. E. coli;

sticky ends are the same in both cases;

fragment of DNA is inserted into the plasmid;

spliced together by ligase;

to make recombinant DNA/plasmids;

recombinants can be inserted into host cell and cloned;

genetic modification is when the DNA/genotype of an organism is artificially changed;

genetic modification alters some characteristic/phenotype of the organism;

named example with modification (e.g. salt tolerance in tomato plants);

benefits: [5 max]

allows crops to be grown where they would not grow naturally;

provides more food;

economic benefits;

expands world’s productive farmland;

reduces the need to clear rainforests to grow crops;

lowers cost of production;

less pesticides/fertilizers/chemicals needed so better for environment;

Award marks for any valid benefit consistent with a named example.

harmful effects: [5 max]

may be released into natural environment;

may affect food chains / unintended effects on other organisms;

may affect consumers e.g. allergies/health risks;

unfair to smaller farmers who cannot compete;

long-term effects are unknown; risk of cross-pollination;

risk of long-term contamination of soil;

Award marks for any harmful effect consistent with the named example.

Few candidates could give much accurate information about karyotyping. Especially overlooked was the importance of selecting cells undergoing mitosis and stopping mitosis at metaphase. Candidates did better in describing an application. Most often, abnormalities in chromosome number or the example of Down syndrome was given.

Candidates tended to do either very well or quite poorly on describing gene transfer. Those who blundered often confused gene transfer with cloning.

Those few who could name an example of genetic modification often struggled to identify specific benefits or harmful effects resulting in generalizations and fictitious accounts. Many answers were incomplete or vague.