Theodor Boveri

Theodor Heinrich Boveri (12 October 1862 – 15 October 1915) was a German biologist who made discoveries in cytology, embryology and genetics. His career was devoted to the processes whereby a new individual arises from parental reproductive materials.
His work with sea urchins showed that it was necessary to have all chromosomes present in order for proper development of the embryo to take place. This discovery was an important part of the Boveri-Sutton chromosome theory. His other significant discovery was the centrosome (1888), which he described as the "especial organ of cell division". Boveri also discovered the phenomenon of chromatin diminution during embryonic development of the nematode "Parascaris".
Boveri–Sutton hypothesis.
1902–1904: Boveri, in a series of papers, drew attention to the correspondence between the behaviour of chromosomes and the results obtained by Mendel. He said that chromosomes were "independent entities which retain their independence even in the resting nucleus... What comes out of the nucleus is what goes into it".
In 1903 Walter Sutton suggested that chromosomes, which segregate in a Mendelian fashion, are hereditary units. E.B. Wilson, who was Sutton's teacher, called this the "Sutton–Boveri hypothesis".
Cancer.
Boveri reasoned that a cancerous tumor begins with a single cell in which the make up of its chromosomes becomes scrambled, causing the cells to divide uncontrollably.
It was only later that researchers such as Thomas Hunt Morgan showed that Boveri was correct.