zygoticallyhttp://www.oed.com/dictionary/zygotically_adv%3Ftab%3Dmeaning_and_usezygotically, adv.
First published 1921; not fully revised

zygoticallyadverb

Biology.
  1. 1915–
    In the zygote; in terms of the zygote.
    Stressed as zyˈgotically.
    1. 1915
      Zygotically therefore the three forms [of rabbit] may be represented thus: Self-coloured..CCSS, Himalayan..CCss, Albino..ccss.
      Journal of Genetics vol. 5 45
    2. 1931
      It is probable that the new combinations will be less successful than the old, both zygotically and gametically.
      Journal of Genetics vol. 24 448
    3. 1980
      The possibility that essential loci in the zeste-white region of the Drosophila melanogaster X chromosome are expressed both maternally and zygotically has been tested.
      Genetics vol. 96 187

Originally published as part of the entry for zygote, n.

zygote, n. was first published in 1921; not fully revised.