Final answer:
The early 1900s was pivotal for the science of genetics because of the rediscovery of Gregor Mendel's scientific discoveries, Thomas Hunt Morgan's identification of the first fruit-fly mutant, and Walter Sutton's proposal that chromosomes contain genes.
Step-by-step explanation:
The early 1900s was pivotal for the science of genetics because of all of the above events. Gregor Mendel's scientific discoveries were rediscovered and recognized as the foundation of modern genetics. Thomas Hunt Morgan identified the first fruit-fly mutant and provided experimental evidence to support the Chromosomal Theory of Inheritance. Walter Sutton proposed that genes are located on chromosomes, further supporting the connection between genes and heredity.