How did nineteenth-century scientists advance the study of chromosomes and mitosis?

Nineteenth-century scientists significantly advanced the study of chromosomes and mitosis through improvements in microscopy and the development of specialized staining techniques.

Key advancements included:

• Technological Innovation: The development of modern achromatic compound microscopes, such as those designed by Ernst Abbe in 1878, provided the necessary clarity to observe fine cellular structures.1
• Staining Techniques: Walther Flemming pioneered the use of aniline dyes to visualize threadlike material within the cell nucleus. By applying these stains to cells at various stages of division, he systematically described the sequence of events he named mitosis.2
• Defining Mitosis: Flemming demonstrated that these threads—later known as chromosomes—shortened and split longitudinally, with each half migrating to opposite sides of the cell. Parallel observations in plant cells were conducted by Eduard Strasburger, who confirmed that nuclei arise only from preexisting nuclei.23
• Meiosis and Heredity: Scientists realized that a mechanism must exist to prevent chromosome numbers from doubling during fertilization. In 1883, Edouard van Beneden discovered that sex cells contain half the number of chromosomes found in body cells, leading August Weismann to propose the existence of a second type of cell division, meiosis, by 1887.4