the presence of the rhd gene in an individual's genome is determined by genotyping. firstly, the body fluid containing an individual's dna will be extracted. dna will then be isolated from unwanted impurities. the isolated dna will then be mixed with various reagents to prepare the polymerase chain reactions (pcr) mixture. the pcr mixture usually contains taq dna polymerase, dna primers, deoxyribonucleotides (dntp) and buffer solution. the dna primers are specific for exon 7 and exon 10. under different circumstances, primers for other regions of the rhd gene, such as intron 4 and exon 5, may also be used. the mixture will be subjected to a series of pcr which is performed by a thermal cycler. by the end of the pcr, the amount of rhd gene will be amplified if it is present. the product of the pcr will be analysed by gel electrophoresis. before gel electrophoresis, dna reference ladder, positive control containing dna with rhd gene and the pcr product will be loaded onto the wells of the gel. an electrical current will be applied and the dna fragments will migrate to the positive terminal as they are negative in charge. since dna fragments have different molecular sizes, the larger they are, the slower they migrate. utilising this property, dna fragments with different molecular masses can be segregated. with the help of gel staining and visualising devices such as uv trans-illuminators, rhd gene dna fragments, if present, will be visible as a band with its corresponding molecular mass. further dna sequencing can be conducted to confirm that the sequence of product dna fragments matches that of the rhd gene sequence.