Theodore Boveri Proves that Different Chromosomes Perform Different Functions in Development

In his paper "Über mehrpolige Mitosen als Mittel zur Analyse des Zelkerns," Verhandlungen der physicalisch-medizinischen Gesselschaft zu Würzburg. Neu Folge 35, 67-90 (1902) 67-90, German biologist Theodor Boveri described experiments involving multipolar mitoses in sea urchin eggs feritized by two sperm. The experiments showed that different chromosomes perform different functions in development, and a full complement of chromosomes is necessary for reproduction.

"In culture, fertilized sea-urchin eggs undergo a complex cell division to form four cells without passing through the normal two-cell stage. This cell division involves four distinct spindle poles and the resulting cells, if gently separated, all have the potential to develop into normal adults. Occasionally, eggs will be fertilized simultaneously by two sperm, and in this case cell division also produces four cells or, more rarely, three. By comparing two populations of fertilized eggs, one exposed to a high concentration of sperm and the other to a low concentration, Boveri saw a direct correlation between the number of resulting deformed embryos and the amount of dispermic eggs.

"Boveri then looked at the development of the individual cells from dispermic eggs when separated at the four-cell stage. Unlike the conventionally fertilized eggs, the individual 'quarter embryos' very rarely developed normally. He also observed that the four separated cells tended to develop differently from each other. Boveri quantified these observations and found that the chance of one of a dispermic egg's quarter embryos developing normally was much greater than that of a dispermic egg as a whole: "certain quarters achieve more separately than all four quarters together".

"The nuclear material of each quarter embryo from dispermic eggs was different, because the chromosomes separated randomly towards the four poles. Boveri hypothesized that each cell needed a full set of chromosomes for normal development. If any chromosomes were missing, the cell would lack 'developmental potential', but duplication of chromosomes would have relatively minor effects, in keeping with Mendel's dominant characters" (http://www.nature.com/celldivision/milestones/full/milestone01.html, accessed 12-16-2013).

J. Norman (ed.) Morton's Medical Bibliography 5th ed (1991) no. 241.1