6 Other variations — copy number
In a second test you will measure gene copy number. Analysis of the human genome sequence (the complete set of genetic information for humans) has led to a surprising and remarkable discovery about the structure of certain regions of the genome. Long segments appeared to be identical to regions elsewhere in the genome. These duplicated segments are complete copies of entire segments of DNA sequence with all the genes in the region being duplicated. In fact, almost 5% of the human genome is made up of this type of duplication. Some segments are present as three or even more copies, and in some cases they can even be completely deleted.
What would you predict would be the level of CYP2D6 enzyme activity in an individual who carried four copies of the CYP2D6*4 gene in total?
Answer
As this version of the gene produces a non-functional protein, even carrying four copies of the gene will still mean this individual has no enzyme activity.
As the number of copies of a gene can vary between individuals, it is perhaps no surprise that it results in differences in the level of RNA being synthesised, with a subsequent increase in the amount of protein being made.
This activity allows you to screen for these two variants in three populations. These data allow you to make comparisons between the populations, predict which individual will have high levels, low levels or no CYP2D6 protein and hence vary in how they metabolise certain drugs. Let’s now learn about the laboratory technique you’ll use – the polymerase chain reaction or PCR.
5 Gene variant