Last updated: April 22, 2013
1879: Mitosis observed
Walter Flemming described chromosome behavior during animal cell division.
Flemming was one of the first cytologists and the first to detail how chromosomes move during mitosis, or cell division. Dividing cells had been observed almost forty years earlier by Carl Nageli, but he misinterpreted evidence of mitosis as something abnormal in the dead cells he'd observed. Flemming observed cell division in salamander embryos, where cells divide at fixed intervals. He developed a way to stain chromosomes to observe them clearly.
Ultimately, Flemming described the whole process of mitosis, from chromosome doubling to their even partitioning into the two resulting cells, in a book published in 1882. His terms, like prophase, metaphase and anaphase, are still used to describe the steps of cell division. His work helped form the basis of the chromosome theory of inheritance.