Flemming, Walther (1843–1905)

German biologist who is best known for his work on the way cells divide; a process that he named mitosis. Using a microscope and aniline dyes Flemming could observe the duplication of chromosomes (the threadlike genetic material in the nucleus) before a cell divides.

He developed advanced techniques for imaging cells using a microscope and staining cells with aniline dyes. These techniques allowed him to describe the nuclear changes accompanying mitosis. In mitosis, the number of chromosomes in the parental cell is first doubled by the process of DNA replication and then, as the cell divides, the chromosomes split into two sets, each daughter cell inheriting an identical set that has the same number of chromosomes as the parental cell (diploid number).

Flemming also proposed an alternative form of cell division, called meiosis, the process of cell division that produces reproductive cells (gametes) with half the number of chromosomes (haploid number). During meiosis, homologous pairs of chromosomes segregate to give gametes with a single set of chromosomes. When a male gamete (sperm) and a female gamete (egg) fuse during fertilization the diploid number is regenerated.

Flemming was born in Sachsenburg and graduated in medicine before becoming professor of anatomy at Kiel University.