It all started with Mendel
The beginning of our thinking of the possibility of genetic
material begins with Mendel.  He described the genetics of
pea crosses, although he did not know what genetic
material was he referred to “factors” as the things which
gave his pea plants their physical characteristics.  While
Mendel’s work gave a logical description of heredity it
was largely ignored for many decades.  His work was
finally reproduced in the early 1900s and was thereafter
regarded as fact