Chromosomes are thread-like structures located within the nucleus of each cell. Chromosomes contain the genetic information necessary to direct the development and functioning of all cells and systems in the body. They pass on hereditary traits from parents to child (like eye colour) and determine whether the child will be male or female.
The Swiss botanist Carl Wilhelm von Nägeli discovered chromosomes in 1842 while researching the formation of pollen. In his 1842 publication he notes the presence of dark substances (chromosomes) in pollen grains that were dividing; he further notes that they are coloured brown when stained with iodine. Here is the original illustration of his observation: