Draw a labelled diagram of the molecular structure of DNA including at least four nucleotides.

A small DNA sample found at a crime scene can be used in an investigation. Describe the steps taken in the processing of this small sample of DNA.

Discuss the relationship between one gene and one polypeptide.

The diagram must show four nucleotides shown with two on each side showing phosphate-sugar backbones and nitrogen base pairs bonded between them.

Award [1] for each of the following clearly drawn and correctly labelled.
phosphate – shown connected to deoxyribose;
deoxyribose – shown connected to phosphate;
(nitrogenous) bases – shown bonded to deoxyribose;
base pairs – shown with labels adenine/A bonded to thymine/T and cytosine/C bonded to guanine/G;
hydrogen bonds – shown connecting bases;
covalent bonds – shown connecting deoxyribose to phosphates;
nucleotide – clearly identified by the candidate;
Award [4 max] if diagram is not shown double stranded.

DNA samples are taken from crime scene, suspects and victims;
polymerase chain reaction/PCR used to increase the amount of DNA;
restriction enzymes used to cut DNA;
electrophoresis involves electric field/placing sample between electrodes;
used to separate DNA fragments according to size;
creating DNA profiles/unique patterns of bands;
comparison is made between the patterns;
criminals/victims can be identified in this way;
DNA is (quite) stable / DNA can be processed long after the crime;

DNA codes for a specific sequence of amino acids/polypeptide;
the DNA code for one polypeptide is a gene;
DNA is transcribed into mRNA;
mRNA moves to a ribosome;
where mRNA is translated into a polypeptide;
originally it was thought that one gene always codes for one polypeptide;
some genes do not code for a polypeptide;
some genes code for transfer RNA/tRNA/ribosomal RNA/rRNA;
some sections of DNA code for regulators that are not polypeptides;
antibody production does not follow this pattern (of simple transcription-translation); (allow other examples)
change in the gene/mutation will affect the primary structure of the polypeptide;

Most candidates correctly answered this question with diagrams that were well done and appropriately labelled.

Many candidates did this question well; most candidates did not mention that DNA samples are taken from the crime scene, the victims and the suspects however; they only mentioned suspects. Many of the candidates were not fully familiar with the actual technique involved in DNA profiling; this might be due to lack of exposure of students to the laboratory working with steps involved in DNA profiling.

This was one of the tough questions for most of the candidate since candidates thought "one gene one polypeptide" scope was only up until explaining the DNA-Gene-codon-polypeptide, most of the students did not  mention the involvement of transcription and translation and exceptions to one gene one polypeptide hypothesis. In other cases, candidates went into great detail to explain transcription and translation (which was not asked for) and completely forgot about the purpose of the question.