Wilhelm Johannsen quotes:

The science of genetics is in a transition period, becoming an exact science just as the chemistry in the times of Lavoisier, who made the balance an indispensable implement in chemical research.

This constitution we designate by the word genotype. The word is entirely independent of any hypothesis; it is fact, not hypothesis that different zygotes arising by fertilisation can thereby have different qualities, that, even under quite similar conditions of life, phenotypically diverse individuals can develop.