Many of the wild potato species cannot be crossed with the European cultivated potato varieties. In most cases this is due to the unequal number of chromosomes of wild and cultivated potatoes. Chromosomes are located in the nucleus of the plant cell and all genetic information is stored in these structures. The common potato has 48 chromosomes, in fact there are 4 sets of 12. Therefore they are called tetraploid. Most wild potato species have 2 sets of 12 chromosomes and are called diploid. To improve the crossability between diploid and tetraploid potato, the chromosome number of a diploid can be doubled. This has been done in other crops and often leads to a yield increase. In potato we have chosen to do it the other way around: when the chromosome number is halved we are able to carry out a breeding program on diploid level, where all kind of diploid species can be introduced. The program on the diploid level takes place in close collaboration with the Wageningen Agricultural University. This program is KARNA’s most important source of increasing the genetic variation in its breeding material. After a few cycles of breeding on diploid level the chromosome number is doubled again to make use of the higher yield capacity of these tetraploid plants.