How a small intestinal roundworm contributed to genetics

Cross-sections at the right place in the uterus of a female Ascaris megalocephala can be used to locate eggs in different stages of the first segmentation mitosis*.

After fixation and coloration of the sections, the chromosomes appear colored. The egg of this parasitic nematode can then serve as a support for studying the chromosomal phenomena that characterize the mitosis.

The main lines of the principle of mitosis have been known for a long time. Edouard Joseph Marie Van Beneden (March 5, 1846 - Liege, April 28, 1910) was a Belgian embryologist, cytologist and biologist. He was Professor of Zoology at the Université de Liège. Through his work on the parasite of the horse, Ascaris megalocephala, a roundworm, he contributed to genetic studies. In this work he discovered the precise function of chromosomes and gametes*. Van Beneden, together with two other scientists, clarified the main facts of mitosis more than one age ago, thanks to the ever-improving design of microscopes, especially at that time.

*Mitosis: a process of cell duplication, or reproduction, during which one cell gives rise to two genetically identical daughter cells. Strictly applied, the term mitosis is used to describe the duplication and distribution of chromosomes, the structures that carry the genetic information. (Encyclopedia Britannica)
*Gamete: a mature sexual reproductive cell