RE SEARCH Research in the potato world for a sample consisting of two tubers or plants/tissue cultures in order to create the requested DNA profile. The laboratory technicians only need a small piece of them. They cut off slices of approx. 0.5 cm from the tubers. If there are many tubers to test, this is done by machine. From the slices, they then punch out a few samples that fit into test tubes. These tubes are then placed into a freeze-drier. The freeze-drying process removes all the moisture from the tissue. This is important, because otherwise the DNA could be lost after defreezing. Variety-specific bar code The potato DNA is unravelled after the pre-processing of the freeze-dried potato samples, as Teunissen demonstrates to us. This is done with state-of-the-art technology. With a holder, which holds eight pipette needles, the laboratory technician can suck up fluid with DNA from eight pipette tubes. The fluid in the needles is then dispersed into a very thin layer of gel, which is placed between two plates of glass. This gel makes the DNA sink down with a variable speed. The speed of sinking depends on the length of the DNA fragment, which causes the variety-specific DNA bar codes. The bar code is made visible with a colouring agent in the fluid, not only to the naked eye, but also to the computer which is connected to the DNA system. Comparing at nine places With the computer, the laboratory technician can enlarge the picture and align the bar codes by pushing one button, The sinking speed of the potato fluid in the needles depends on the length of the DNA fragment, which causes the variety-specific DNA bar codes. When the computer spots a DNA profile that is already in the database, it automatically displays the relevant name. 24 Potato World 2012 • number 3 Pagina 23
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