Probability of monozygotic twinning as a reflection of the genetic control of cell development

The stability of the incidence of monozygotic twinning (MZT) suggests that its origin is genetically, rather than environmentally, controlled. Available data, though scant, supports our hypothesis that the MZT probability is (1/2)K, where K is a species-specific integer parameter. For humans MZT occurs in about four of 1000 births, which is close to one occurrence in 2(8) births, i.e. K = 8. The environmental factors are not the cause of MZT, but may influence its expression. When this influence is in effect under some extreme experimental conditions the above form of MZT probability is observed. Binary structure of the MZT probability provides insight into genetic control mechanism of cell division.