Final answer:
The leading theory of inheritance in the 19th century was the blending theory of inheritance, which was later debunked by the Chromosomal Theory of Inheritance proposed by Walter Sutton and Theodor Boveri, leading to the development of genetics.
Step-by-step explanation:
19th Century Theory of Inheritance
The leading theory of inheritance during the 19th century, prior to the rediscovery of Gregor Mendel's work, was the blending theory of inheritance. This theory suggested that the traits of the parents would blend together in their offspring, producing an intermediate characteristic. For instance, if one parent was tall and the other was short, the theory predicted that their children would be of average height. This idea appeared to make sense because of continuous variation in traits such as height, which results from the action of many genes.
However, this theory had several flaws, mainly that it did not explain how traits could re-emerge after several generations, nor how variation was maintained in a population. Walter Sutton and Theodor Boveri disproved the blending theory with the Chromosomal Theory of Inheritance in the early 20th century. Their observations during mitosis and meiosis, along with the work of other scientists like Thomas Hunt Morgan, demonstrated that chromosomes carry units of heredity, known as genes, which determine the traits of offspring.
The Chromosomal Theory of Inheritance became the cornerstone for the field of genetics, shifting the scientific understanding of heredity from the blending of traits to the segregation and independent assortment of genes as the basis of inheritance.