In the 1830s, Gregor Mendel, a Moravian monk, conducted experiments cross-breeding peas. He determined that certain traits, such as color, shape, and size, were passing from the parents to their offspring in a predictable way. We now call them genes . Mendel observed that the traits of the parents did not blend in the offspring. Mendel hypothesized that each organism has a pair of factors that determine each trait.
Offspring receive one half of each pair from each parent.
In the offspring, the two factors, or genes, work together. Although Mendel recorded his observations, published them, and sent them to many leading institutions, his work was ignored. Mendel's work was rediscovered around the turn of the century. However, it was still unclear what the precise agent of inheritance was and how it functioned. In 1907 Thomas Morgan demonstrated that the controlling mechanisms of inheritance are contained in chromosomes inside each cell.