Introduction Gregor Johann Mendel – a multitalented scientist, considered the "father of modern genetics", was born in 1822 and recent bicentennial anniversary of his birth provided a unique opportunity to remind the legacy of this great scientist. Mendel made the key discoveries in the Augustinian Abbey in Brno, Czech Republic, but a key role enabling his discoveries played his knowledge of mathematics, physics and statistics, which he obtained at the University of Vienna, Austria. Application of his interdisciplinary knowledge and tremendous experimental work involving a hybridization of about 28,000 pea plants led to a formulation of the generally accepted principles of heredity.

In chronic lymphocytic leukemia (CLL), the worst prognosis is associated with TP53 defects with the affected patients being potentially directed to alternative treatment. Therapy administration was shown to drive the selection of new TP53 mutations in CLL. Using ultra-deep next-generation sequencing (NGS), we performed a detailed analysis of TP53 mutations’ clonal evolution. We retrospectively analyzed samples that were assessed as TP53 -wild-type (wt) by FASAY from 20 patients with a new TP53 mutation detected in relapse and 40 patients remaining TP53 -wt in relapse. Minor TP53 -mutated subclones were disclosed in 18/20 patients experiencing later mutation selection, while only one minor-clone mutation was observed in those patients remaining TP53 -wt ( n =40). We documented that (i) minor TP53 mutations may be present before therapy and may occur in any relapse; (ii) the majority of TP53 -mutated minor clones expand to dominant clone under the selective pressure of chemotherapy, while persistence of minor-clone mutations is rare; (iii) multiple minor-clone TP53 mutations are common and may simultaneously expand. In conclusion, patients with minor-clone TP53 mutations carry a high risk of mutation selection by therapy. Deep sequencing can shift TP53 mutation identification to a period before therapy administration, which might be of particular importance for clinical trials.