How much was known about chromeosones and genes in Mendels time?

In Mendel's time (mid-19th century), the concepts of chromosomes and genes were not yet understood. Mendel conducted his experiments on pea plants and discovered the basic principles of heredity, such as the laws of segregation and independent assortment, without any knowledge of the underlying mechanisms. The discovery of chromosomes as carriers of genetic information and the concept of genes as units of heredity emerged later, particularly in the early 20th century with the advent of cytogenetics and the understanding of DNA.