While we strived to explain the concepts of Solynta’s breakthrough as simple as possible we cannot avoid to use some terminology specific to the field. We try to accommodate the reader by providing a glossary of terms and a refresher on some secondary school genetics. If you are familiar with the subject you can easily skip this chapter.

Everybody heard of DNA, the carrier of genetic information. DNA is organized in chromosomes and the informative parts of the genetic information are called genes, which are located on a specific area of a chromosome which is called the locus. Genes can have different manifestations called alleles, indicated by letters, for example A or a.

An organism can have two sets of chromosomes eg human. This is called diploid (one chromosome is contributed from the father, the other from the mother.

An organism can have four sets of chromosomes eg cultivated potato. This is called tetraploid.

If the genes on both chromosomes are identical we call this homozygote (AA in this case).

If the genes on both chromosomes are different we call this heterozygote (Aa in this case).

The sex cells (gametes) of a diploid organism contain only one set of chromosomes. The female organs (placenta) form egg cells and the male organs (anthers) form pollen cells.

Upon crossing, the pollen lands on the style of a flower, grows into the flower  towards the placenta and fuses with the egg cell. This results in an embryo of the new generation, that is diploid again.

In this case a plant with a homozygote locus AA is crossed with a plant with homozygous aa for the same locus. This results in a heterozygous progeny: AA x aa -> Aa. This is the usual way to make hybrids. These are genetically heterozygous but uniform.

If a plant with a heterozygous locus is crossed with another plant with a heterozygous locus (or selfed) the progeny segregates into  Aa x Aa -> 25% AA + 50% Aa + 25% aa

When the progenies are selfed again the homozygous plants can only get homozygous plants upon selfpollination, while the heterozygous plants will segregate into 50% homozygotes and 50% heterozygotes. As a consequence the level of heterozygosity is halved in each generation of self-pollination. After 6 or 7 generations of selfing the plants are nearly completely homozygous. In tetraploid potato (ABCD) it takes seven generations to reach 50% homoz​ygosity.

Here we have a homozygous plant with the trait of producing red flowers, coded RR; white flowers are coded rr.
At the tuber locus the alleles are tt, indicating small tubers.
The sex cells have only one set of chromosomes: Rt

Here we have a homozygous plant with the trait of producing large tubers, coded TT and white flowers: rr
The sex cells have only one set of chromosomes: rT

De sexcells are Rt and rT. Upon fertilization, the sex cells of the parents merge and from a progeny plant. Tr + tR -> TtRr

The cross is now very predictable resulting in a heterozygous plant with large tubers and white flowers.

The cultivated potato has four sets of chromosomes, which is called tetraploid.
In traditional potato breeding two heterozygous tetraploid cultivars are crossed.
It does not take much imagination to see that a heterozygous tetraploid crossing is extremely unpredictable, especially when one considers that potato genome has over 30,000 genes.
The development of a new cultivar of potato with a gene, introduced from a wild species by crossings and selections, takes 15 to 30 years.

One of the key elements in the Solynta breeding method is the development of diploid homozygous potato plants which can be used as parents (elite breeding line) to produce an F1 hybrid cultivar. In principle, this is done exactly the same as is done for years in many other crops, for example tomato. Up until the breakthrough by Solynta this was previously deemed impossible due to the severe inbreeding depression and self-incompatibility. Solynta has proven that these hurdles can be overcome and F1 potato hybrid cab be produced.

To overcome the unpredictable outcome of crosses between heterozygous tetraploid parent plants, in traditional breeding, only one progeny plant is selected and multiplied by vegetative propagation. With a multiplication factor of a factor ten per year, it requires many years to build the seed tubers for a new variety.
The Solynta multiplication can be done by repeated crosses between homozygous parents, which requires only one generation (six months) to build enough seeds of a new variety to fulfill the needs of the market.