Final answer:
Research after Mendel linked genes to chromosomes, supported by Thomas Hunt Morgan's experiments with fruit flies, leading to the Chromosomal Theory of Inheritance and explaining the independent assortment of traits.
Step-by-step explanation:
Research conducted after Gregor Mendel revealed fundamental similarities between genes and chromosomes. Mendel's foundational experiments using pea plants in the 19th century illuminated key principles of heredity, though he did not know the physical basis for these phenomena.
Later improvements in microscopy allowed scientists to visualize chromosomes during cell division, relating these structures directly to Mendel's abstract principles. Thomas Hunt Morgan's work with Drosophila melanogaster helped prove that chromosomes were indeed the carriers of genes, consolidating the Chromosomal Theory of Inheritance.
This theory posits that chromosomes, which we now understand to consist of DNA, bear the genetic material responsible for hereditary traits. It was also discovered that genes on a chromosome can be linked and, despite linkage, they can be separated by homologous recombination during meiosis, explaining the independent assortment of traits.