All Cesky Terriers descend from four bitches, Lovka, Lapka, Ulrika and Urana Lovu zdar.
Since these bitches are all the product of close inbreeding back to the Sealyham Terriers, Buganier Urquelle and Jasans Amorous Artilleryman, and the Scottish Terrier, Scotch Rose, and given that only two known outcrosses have been admitted since then - to the Sealyham Terrier Andra z Rastamoru (1984/5) and a crossbred male that is thought to have mated Bellis Sollor(in 1972) it is obvious that the gene pool of the Cesky Terrier is very limited.
A further restriction of genetic diversity occurred in the Czech Republic towards the end of the 1970s. There were few viable stud dogs and the bitches were old and infertile. Added to this was the newly introduced threat of parvovirus. The breed was saved by the dog Cedro Bohemicus, who was mated to virtually every bitch available.
Because of this, Cesky Terrier breeders must be very careful that they don't restrict the gene pool even further. It is very tempting, if there is a top-winning male of superior breed type, to mate many bitches to this dog. However, this can be a recipe for disaster - and is known as Popular Sire Syndrome